1
1.
Executive Summary
_________________________________________________________________________________
The planet Earth has a long and violent history of collisions with extraterrestrial bodies such as
asteroids and comet nuclei. Several of these impacts have been large enough to cause major
environmental changes, causing mass extinctions and severe alterations to weather patterns and
geography.
Every day the Earth is bombarded by debris from space, but the vast majority of objects entering the
atmosphere are tiny, and burn up long before they reach the ground. However, larger bodies will
penetrate deeper into the atmosphere, and can detonate with tremendous explosive force. The object
that devastated 2000 square kilometres of Siberian forest in 1908 was only 60-metres in diameter,
and exploded with a force of 12.5 megatons of TNT, a thousand times the power of the Hiroshima
atomic bomb. The resulting damage template almost fits inside the M25 motorway around London.
Figure 1 - The destruction Template from the 1908 Tunguska event
superimposed over London
But objects this small present a threat only to a limited area. Objects with diameters greater than one
kilometre pose a threat to the entire globe, and can be expected to collide with the Earth with a
statistical frequency of 100,000 years.
The immediate effects of a major impact, including blast, firestorms, intense acid rain, the production
of pyrotoxins and the destruction of the ozone layer, coupled with the possible triggering of volcanism
and seismic activity will cause a significant environmental disaster and massive loss of life and
property. However, it is the vast amount of dust and debris injected into the upper atmosphere,
blocking the Sun and causing phenomena similar to the nuclear winter scenario that could threaten
the ecosphere on a global scale. Many smaller strikes, though not globally threatening, have caused
massive damage to the area of impact, and often at considerable distance. Two thirds of the Earth's
2
surface is covered by water, and a major impact at sea will have far-reaching and catastrophic effects
due to the production of a massive tsunami by the force of the impact. The spread of human
settlement, civilisation, and particularly urbanisation, makes it much more likely that a future impact,
even relatively small, could result in the massive loss of human life and property. There is currently
no co-ordinated international response to this threat, and in the United Kingdom, there is little or no
official recognition of the hazard.
The aim of this paper is to examine the potential threat to the national and global environment posed
by cometary and asteroidal impacts, measures currently in place to address the problem, and planned
enhancements to the system, with a view to making recommendations concerning United Kingdom
participation in the international programme at a national level.
3
2.
Introduction
_________________________________________________________________________________
The notion that an asteroid or comet with enough energy to cause a national or global catastrophe
may hit the Earth has, until recently, been regarded as in the realms of science fiction as opposed to
science fact. Indeed, the impact origin of lunar craters has only been widely acknowledged in the
second half of this century. However, studies conducted over the last fifteen years clearly indicate that
such an event is not merely possible, but inevitable. The reality of major impacts in the solar system
was starkly demonstrated in July 1994 when the fragments of Comet Shoemaker-Levy 9 collided with
the planet Jupiter.
The impact history of the Earth is now a matter of record, and there is no reason to assume that the
threat is any less in the present than it
was in the past; the only question is
one of timing - when will the next
major
impact
occur?
Serious
investigations into the nature and
numbers of Near-Earth Objects (NEO)
have only recently begun, and are far
from complete, but the results of these
studies already give considerable
cause for concern, especially over the
long term.
The assessment of any threat is
based on two major factors:
The likelihood
becoming reality
q
Figure 2 - Meteor Crater, Arizona
q
of
the
threat
The consequences were it to do
so.
In the case of a globally threatening impact, the likelihood is low, but the consequences are potentially
catastrophic to the entire ecosphere, and to the survival of multiple species, including humankind.
Impacts by smaller bodies could have devastating consequences on a national scale, and can be
expected relatively more frequently. On this basis, the potential threat requires, at least, thorough
investigation.
The American Institute of Aeronautics and Astronautics (AIAA) Position Paper "Response to the
Potential Threat of a Near-Earth-Object Impact" contains the following passage:
"If some day an asteroid does strike the Earth, killing not only the human race but millions of other
species as well, and we could have prevented it but did not because of indecision, unbalanced
priorities, imprecise risk definition and incomplete planning, then it will be the greatest abdication in all
of human history not to use our gift of rational intellect and conscience to shepherd our own survival,
and that of all life on Earth."
4
3.
The Threat
_________________________________________________________________________________
All bodies in the solar system with visible, solid surfaces show extensive evidence of cratering (with
two exceptions - Io, a moon of Jupiter, which is being resurfaced by volcanically produced sulphur,
and Europa, another Jovian moon, which has a surface of water ice). On Earth, we see very few
obvious craters because geological processes such as volcanism and erosion soon destroy the
evidence. On bodies with little or no atmosphere, such as Mercury or the Moon, craters abound, and
even on Venus, with its enormously dense atmosphere, there is stark testimony to major impact
events. There is strong evidence that there was a period of intense bombardment in the inner solar
system that ended about 3.9 billion years ago. Since then, cratering appears to have continued at a
slower, but fairly uniform rate. The cratering
records, as witnessed on other Solar System
bodies, should be viewed with care given the
protective shield of the Earth's atmosphere, but the
indications are clear. The atmosphere protects the
surface from the multitude of small debris, the size
of grains of sand or pebbles, about 100 tons of
which impact with the planet every day. Meteors in
the night sky are visible evidence of small debris
burning up high in the atmosphere, while smaller
particles decelerate more gently in the upper
atmosphere, and settle slowly to the ground. Up to
a diameter of about 100 metres, most stony
meteoroids are destroyed in the atmosphere by
Figure 3 - Mercury
pressure induced explosions, though some
fragments can reach the ground as stony
meteorites.
So, what is going to do the killing after a major
impact?
Immediate effects will include the
obvious explosive effects at ground zero and
local firestorms raised by the superheated air
from the impact. A crater, about 20 times the
diameter of the impacting body, will be
excavated in a matter of seconds, and debris will
be ejected into sub orbital trajectories. This
debris will later re-enter the atmosphere – the
meteor shower from hell - possibly all over the
globe raising massive fires that destroy a
significant proportion of the biomass. Intense
acid rain would result from the ionisation of the
air as the impactor entered the atmosphere, as
would the production of pyrotoxins. The ozone
layer would be severely damaged, and major
Figure 4 - Aorounga Crater, Chad
volcanism and seismic activity can be expected
as the shock wave of the impact ripples through
the planet. All of this will cause a global
environmental disaster of extreme severity. In addition to most or all of these effects, an impact at sea
will produce a significant "tsunami," capable of travelling considerable distances, and possessing
enormous energy. Such surges will pose a substantial threat to low lying and coastal areas. The
United Kingdom, with much of its population and economic infrastructure located in precisely such
areas, would be at particular risk from an impact anywhere in the Atlantic Ocean. Japanese research
indicates that there is a one- percent chance that every major city on the Pacific Rim will receive
catastrophic damage from an impact-induced tsunami at some stage during the next hundred years.
However, the main killing mechanism will be the vast amount of dust and debris injected into the
upper atmosphere, combined with the smoke from the firestorms (witness recent events in Indonesia).
These will obscure the Sun and cause a phenomenon similar to, but much more severe than the
“nuclear winter” that became such an issue during the Cold War. It is this that is likely to pose the
5
greatest threat to the ecosphere on a global scale as food chains collapse and darkness, cold and
starvation set in.
Figure 5 - Earth, with the G-Impact scar from Jupiter's encounter with Comet
Shoemaker-Levy 9 superimposed.
After a few months or years the atmosphere will clear, but the surface of the Earth, now mainly white
in colour, might reflect too much of the Sun's radiation to prevent a new ice age. However, there are
other mechanisms at work. The atmosphere will contain a substantial excess of CO2, resulting from
the global fires, the release of the gas from carbonate rocks and vulcanism. The Earth could be in for
a massive overdose of greenhouse effect. The balance between sweltering and freezing is a very fine
one.
Such globally threatening events can be expected on time scales of 100,000 years.
Smaller strikes, in the 50-100 metre range, though not globally threatening, have in the past caused
massive damage to the area of impact, and often at considerable distance. We saw this at Tunguska
in 1908 and in the Amazonian Rain Forest in 1930. The spread of human settlement, civilisation, and
particularly urbanisation, makes it much more likely that a future impact, even relatively small, could
result in the massive loss of human life and property. The time scale for such impacts is between 50
and 100 years.
Even much smaller impacts can have significant effects. Typically a 10-metre diameter body will have
the kinetic energy of about 100 kilotons, Hiroshima was 150 kilotons, and is likely to detonate at an
altitude above 10 km, causing little or no damage on the ground, but considerable alarm to those who
6
witness it as was seen on 9 October 1997 in El Paso, Texas. Such events have been recorded by US
surveillance satellites at the rate of one or two per month, and smaller Kiloton sized explosions
happen every 1 to 10 days.
There are now more than 150 ring like
structure structures on the Earth identified
as definite impact craters. However, most
of them are not obviously craters. Their
identity has been masked by heavy erosion
over the centuries, but the minerals and
shocked rocks found nearby confirm that
they were caused by massive impacts. The
Ries Crater in Bavaria is a lush green basin
some 25 kilometres (15 miles) in diameter
with the city of Nordlingen in the middle.
Fifteen million years ago a 1500 metre
asteroid or comet impacted there,
excavating more than a trillion tons of
material and scattering it over the northern
hemisphere. This sort of event is thought to
occur about once every 100,000 years. A
step up the threat scale is the type of
impact that created the Chicxulub crater in
Mexico some 65 million years ago. This is
the event that destroyed up to 70% of
species then living on the planet, including
the dinosaurs. Impacts on this scale are
thought to occur once every 50 -100 million
years. Chicxulub is currently the largest
known crater that has a confirmed impact
origin, but there are several other larger
ring-like structures about which geologists
are, as yet, uncertain.
Figure 6 - A small bolide detonates over Los
Angeles.
Currently there are more than 200 asteroids
known to have orbits that cross that of Earth,
though, being a three dimensional problem, this
does not necessarily mean that a collision is
inevitable. They range in diameter from a few
metres up to 9 kilometres (1620 Ivar). A working
group chaired by Dr. David Morrison of the NASA
Ames Research Center, estimates that there are
some 2,100 such asteroids larger than one
kilometre and perhaps 320,000 larger than 100
metres. An impact on the Earth by one of the
smaller bodies would be a local or regional
catastrophe, but it would not be globally
threatening. However, the working group
concluded that an impact by a body larger than
about two kilometres would, in addition to the
immediate effects of the collision, significantly
degrade the global environment to the extent that
the survival of a significant proportion of the
Figure 7 - The Chicxulub Crater in Mexico
human population would be put at serious risk. An
impact by an object larger than about five
kilometres would inevitably lead to mass extinctions on a large scale. More recently, partly due to the
results of the Shoemaker-Levy 9 impact on Jupiter, the threshold for a globally threatening body has
been reduced to a diameter of about one kilometre.
An individual's chance of being killed by the effects of an asteroid or comet impact is small, but the
risk increases with the size of the impacting body, with the greatest risk associated with global
7
catastrophes resulting from impacts of objects larger than one kilometre. Calculations have been done
relating to the relative probabilities of a citizen of the USA dying from a variety of causes. The results
are shown in Table 1.
Cause of Death
Motor Vehicle Accident
Homicide
Fire
Firearms Accident
Electrocution
Aircraft Accident
Asteroid Impact
Flood
Tornado
Venomous bite or sting
Fireworks accident
Food Poisoning
Probability
1 in 100
1 in 300
1 in 800
1 in 2,500
1 in 5,000
1 in 20,000
1 in 25,000
1 in 30,000
1 in 60,000
1 in 100,000
1 in 1 million
1 in 3 million
Table 1: Causes of Unnatural Death in the USA
These figures (after Chapman and Morrison) were accepted at the time, but a growing number of
scientists feel that the figure for Asteroid Impact is too low by a likely factor of two, and should be
closer to one in 10,000. The figures also fail to demonstrate the qualitative difference between
individual events, such as the majority of cases in the table above, and the sudden, but massive loss
of life caused by a major impact event.
Science knows of no asteroid or comet likely to collide with Earth in the short or medium term, but the
number of known Earth crossing asteroids is small when compared with the total population. Even if it
is assumed that the probability of a major collision is small, the global nature of the threat makes the
assessment of its true nature an urgent priority.
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4.
Asteroids
_________________________________________________________________________________
4.1.
Origin
Most asteroids are believed to be
the remnants of the material from
the
circumstellar
disk
that
coalesced to form the planets.
Former theories involving the
break-up of a planet between Mars
and Jupiter have now been
discounted.
They
therefore
represent samples of the primordial
solar system, largely unchanged
since its formation 4500 million
years ago. In addition, there is
evidence that some asteroids are
related to comets, being either
debris ejected from the parent
body, or inert comet nuclei.
4.2.
Size and Composition
Figure 8 - Ida
The sizes of asteroids range from
dust particles to significant bodies up to the largest, Ceres, which is 913 kilometres in diameter. Their
composition can be determined by the spectrum of the sunlight that they reflect. There are four main
types:
C-Type.
These
dark,
carbonaceous bodies are mainly
found in the outer regions of the
main asteroid belt. The class
includes Carbonaceous Chondrites
that have a similar chemical
composition as the Sun (without
hydrogen or helium) and that are
thought to be primitive unprocessed
material from the formation of the
Solar System. The class may also
include old, inactive comet nuclei.
With albedos of around 5%, C - type
asteroids are dark and difficult to
detect optically. They form about
75% of the total population.
S-Type.
S-type
asteroids
tend to be grey in colour, with
Figure 9 - Gaspra
intermediate albedos. They are
composed mainly of silicaceous
material, and are commonly known
as stony asteroids. Found mainly in the inner regions of the main asteroid belt, S-types form about
15% of the total population.
M-Type.
M-type asteroids are metallic in nature with moderate albedos. They make up some
10% of the total asteroid population.
Composite.
These bodies display the characteristics of more than one type, and may be the result
of coalescence or collision.
9
4.3.
Orbital Characteristics
The majority of asteroids are confined to the main asteroid belt, orbiting the sun between Mars and
Jupiter. The orbits of these main belt asteroids are generally stable, but mutual interaction or the
gravitational influences of Mars or Jupiter can perturb them. However, there are significant groups of
Figure 10 - An Amor asteroid approaches Mars
asteroids that are found elsewhere, particularly the Aten and Apollo families that have orbits that cross
that of the Earth. Another group, the Amors, do not currently have Earth crossing orbits, but orbital
evolution will make impacts possible in the future. The estimated numbers of such asteroids with
diameters over one kilometre, and those discovered (of any size) up to December 1992, are shown in
Table 2.
NEO Class
Estimated Population
Number Discovered
Aten
100
21
Apollo
800
169
Amor
1500
132
Table 2.
Earth Crossing Asteroid Families
Discovery rates have increased exponentially since the establishment of projects such as Spacewatch
and NEAT and LINEAR.
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5.
Short Period Comets
_________________________________________________________________________________
Figure 11 - Comet Halley
5.1.
Origin
Short period comets are thought to originate in the Edgeworth-Kuiper Belt, situated 35 to 1000
Astronomical Units (one AU is the average distance between the Sun and Earth - about 150 million
kilometres) from the Sun (starting just beyond the orbit of Neptune). It is also believed that the orbits
of some long period comets may be gravitationally perturbed, making them indistinguishable from
their short period relatives. Their orbits are usually
stable within this wide band, but the occasional (and
chaotic) gravitational effects of the outer planets cause
these bodies to alter their paths into highly elliptical
orbits that take them close to the Sun. Such events are
unpredictable, and it has recently become clear that
comets have very low albedos, making them difficult to
detect optically. However, as they heat up in the inner
solar system they begin to outgas forming extensive
clouds of dust and gas known as "comae", making
them fairly easy to detect.
5.2.
Composition
All comets are believed to share roughly the same
composition, having formed from essentially the same
pool of material. They have been described as "dirty
snowballs", a description reinforced, but complicated
by the detailed studies of Comet Halley in 1986. "Icy
mud-ball" may be a more accurate description. The
main constituents of nuclei are volatile ices, mainly
water, mixed with dust and hydrocarbons. The one
nucleus that has been closely studies (Comet Halley)
is blacker than coal, due to a coating of dark
Figure 12 - The nucleus of Comet
Halley
11
hydrocarbons. Until the Giotto mission in 1986 that photographed Halley, it was assumed that
cometary nuclei would have high albedos, due to their icy composition. The very low albedo of Halley
has caused a reassessment, and a consequent upward revision of size and mass estimates of
cometary nuclei. The increased temperatures encountered as the nucleus approaches the Sun cause
volatile ices to sublime, releasing gas and dust which form a cloud, or coma around the nucleus, and
the dust element of the "tail" popularly associated with comets. The other element, the plasma tail, is
caused by the interaction of the solar wind with ions released from the nucleus during outgassing.
5.3.
Orbital Characteristics
The average short period comet has an orbital period measured in years or decades (up to 200
years). There are two major families, the Jupiter family with periods of less than 20 years, and the
Halley family with periods between 20 and 200 years. The vast majority of short period comets have
orbits inclined to the ecliptic by an angle of less than 350. Once found, the orbit of such a comet can
be predicted with some accuracy. However, several factors inject elements of uncertainty into the
calculations. The first are the chaotic effects of the gravitational influences of major bodies in the solar
system. In extreme cases comet nuclei may be broken up, as witnessed by Comet Shoemaker-Levy 9
that later impacted with Jupiter. The second mechanism is well understood, but even less predictable.
One effect of the outgassing of volatile compounds is to produce thrust, as though the comet were
powered by steam jets. Although minuscule, over time this thrust can significantly affect the orbit of a
comet.
12
6.
Long Period Comets
_________________________________________________________________________________
6.1.
Origin
Long period comets are thought to originate
in a spherical cloud of debris that surrounds
the Sun at distances between 20,000 and
100,000 AU (almost two light years - half way
to the nearest star). The gravitational
perturbation that causes such bodies to leave
the cloud and approach the Sun is thought to
be provided by the relative movement of
nearby stars, massive dust clouds or the
shock wave from an explosive event such as
a supernova. Whatever the mechanism, five
to ten significant cometary bodies approach
the Sun each year, while an unknown
number of smaller bodies pass undetected.
6.2.
Composition
The composition of long period comets is
Figure 13 - Comet Hale-Bopp
very similar to that of their short period
companions, but they tend to contain more
volatiles. Short period comets outgas huge quantities of their volatiles at each approach to the Sun, so
they eventually run out, becoming asteroid-like bodies. (There is still some doubt over the relationship
between dead comets and some classes of asteroids). Long Period comets visit the inner solar
system only rarely, so retain much of their icy material (and mass).
6.3.
Orbital Characteristics
Unlike short period comets, whose orbits are relatively close to the ecliptic, long period comets have
orbits that are randomly orientated on the celestial sphere. Their orbital periods are longer than 200
years, and they will often only return after thousands or even millions of years (or not at all).
Consequently, most long period comets will be new to science when they reappear in the inner solar
system, and have yet to be catalogued.
Figure 14 - The coma of Comet Hale-Bopp
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7.
Cometary Debris
_________________________________________________________________________________
There is increasing evidence that the disruption or
disintegration of cometary bodies such as that
witnessed with Comet Shoemaker-Levy 9 (that later
impacted on Jupiter in July 1994) is a more
common occurrence than previously suspected. All
comets leave trails of debris as they travel through
the solar system, and these cause annual "meteor
showers" as the Earth passes through their path.
Meteors are caused by small particles, most no
larger than pebbles, but there is a strong possibility
that larger fragments may be interspersed with
them. It is unlikely to have been a coincidence that
the 1908 Tunguska event occurred at the height of
the Taurid meteor shower, associated with the
periodic Comet Encke. The same comet has been
linked with a number of probable events that have
occurred during recorded history.
Should a large comet nucleus shatter, for whatever
Figure 15 - A Perseid meteor
reason, as seen with Comet Shoemaker-Levy 9, it
will produce a stream of fragments in its wake.
These will, over time, spread out along the orbital path, and are likely to vary in size from a few
microns to a few hundreds or thousands of metres in diameter. Such a debris stream could pose a
Figure 16 - Comet Shoemaker-Levy 9
significant and recurring threat to the Earth.
There is increasing evidence (Bailey and Emel-Yanenko, 1997) that there might be a significant
population of "dead" comets occupying Halley type orbits. Once a comet has outgassed all of the
available volatiles, its coma and tail will disappear, and the remaining, inert nucleus will take on the
appearance of a low albedo asteroid. Finding such bodies could present new challenges to search
programmes, requiring the use of infrared technology.
14
8.
Impact Probability & Impactor Size
_________________________________________________________________________________
The raw probability of a particular NEO colliding with the Earth is easy to calculate mathematically.
The cross-sectional area of the Earth is approximately one part in 2.2 billion of the area of a sphere
surrounding the Sun with a radius of one AU. Any Earth crossing asteroid will cross the Earth's orbit
twice per revolution; therefore, for any randomly orbiting body there is a 1.1 billion to one probability of
collision. The gravitational attraction of the Earth, and the fact that most asteroids have orbits that are
at moderate inclinations to the Earth's plane increase this probability to an estimated 100 million to
one. There are, however, a number of other factors that make this calculation suspect. Indeed, the
whole subject is very complex, and poorly understood at this time.
Sub-Critical Impactors (SCI) are objects that impacts with the surface of the Earth, or have an effect
on that surface, that have diameters of less than 1 kilometre. In addition to asteroids and comets
there is increasing evidence (Bailey and Emel-Yanenko, 1997) that there is a significant population of
"dormant" comets occupying Halley type orbits. These objects will have low albedos, and will
consequently pose a substantial problem for observational analysis.
Near Earth asteroids (NEAs) are main belt asteroids or fragments of main belt asteroids injected into
Earth crossing orbits by gravitational perturbation or mutual collisions. Their lives can be ended by
collision with a planet or the Sun, collision with another asteroid or by ejection from the solar system
resulting from gravitational perturbation (probably by Jupiter). These processes result in expected
NEO lifetimes of 10 to 100 Myr. To have maintained the near constant SCI impact flux since the end
of the late bombardment era some 3 GYr ago, there must be some method by which the NEO
population is constantly replenished to negate the effects of attrition. It is fairly certain that Jupiter
plays a key role in the deflection of main belt asteroids and short period comets onto Earth crossing
trajectories, and the estimates of inbound flux agree well with the calculated replenishment rates
required.
The observational population census for Earth crossing objects is only complete for objects in the 8kilometre diameter range (such as 1627 Ivor) or larger. The detection completeness for 1 kilometre
range is estimated to be in the region of 12%. However, as pointed out by Rabinowitz et al in 1994,
population estimates will also be limited by the completeness of the sample studied, which will be
biased towards the most easily observed NEOs; the largest and brightest. Purely observational
methods are therefore currently inadequate for an accurate estimate of sub-1 kilometre objects.
There are, however, two methods by which estimates can be made. Populations can be estimated
from extrapolation of the limited observational results and theory. These estimated populations,
coupled with the calculated dynamical lifetimes of the target objects produce estimates of flux for
specific size ranges (Bowell & Morrison). Alternatively, the integrated impact flux over the past 3 GYr
can be determined empirically by analysing crater density and distribution on Lunar maria.
The Rabinowitz et al estimates are shown in Figure 17, and in tabular form in Table 4.
109
108
107
106
105
104
103
102
101
100
10-2
10-1
100
101
Figure 17. Estimated number of Earth-crossing asteroids N
larger than a given diameter.
15
Asteroid Diameter
(m)
101
102
103
Estimated Population
M&R
Steel
2.5x108
1.5x108
1.4x105
3.1x105
3
1.5x10
2 x103
Estimated Impact
Frequency (yr)
1-5
103
105
Table 4. Asteroid population and impact frequency as a function of diameter. (After Morrison
& Rabinowitz, and Steel)
Bowell and Muinonen have derived a population for objects with diameters between 10 and 1000
metres of 2.6 x 108, which is in close agreement with the Spaceguard Report model. Both figures lie
well within the estimated errors of both models.
Asteroid Diameter
3m
10m
30m
100m
300m
Month
Year
Typical Impact Interval
Decade
Century
Tunguska
1 km
3 km
10 km
NEO diameter estimation relies
on knowledge of the likely
albedos
of
the
objects
concerned. D. Rabinowitz et al
used the same albedo range as
found in main belt asteroids
(McFadden et al 1989), and
deduced size and population
data
consistent
with
the
Shoemaker model.
Millennium
The size-frequency distribution
figures
published
by
Shoemaker
in
1983,
and
used
10 y
in the Spaceguard Survey
Report (Morrison 1994) are
10 y
generally accepted within the
10 y
scientific community.
Their
K/T Impact
results
are
shown
in
Figure
18.
10 y
More recent observations of
small earth crossing objects
Figure18. Frequency curve for impacts on the Earth. The solid line is
from Shoemaker (1983). The dotted line is taken from Steel 1995
reported by Rabinowitz (1993)
and Rabinowitz et al (1993)
have suggested a modest enhancement in the 10 metre size range, but these rarely penetrate the
atmosphere, except in the case of iron meteoroids, so the Shoemaker figures retain their validity for
the purposes of this paper. The limited observational data available is in agreement with the lunar
cratering record to a significant degree of accuracy.
10 4 y
5
6
7
8
Date
1930
1937
1947
1965
1966
1969
1972
Location
Brazil
Estonia
Sikhote-Alin
Revelstoke
Kincardine
College, Alaska
Grand Teton
1990
1992
1994
1997
1997
Sterlitamak
Peekskill
Micronesia
Texas
Greenland
Comments
Tunguska like airburst, with significant ground damage
8.5m crater from fragment of ~50t body.
100 1-14m craters. Iron meteorite.
High airburst. No physical damage on ground.
High airburst. No physical damage on ground.
High airburst. No physical damage on ground.
Object tracked 1500 miles through atmosphere before bouncing
off.
5m crater produced
Bolide witnessed across eastern USA. Minor damage on ground.
High airburst. No physical damage on ground.
High airburst. No physical damage on ground.
Medium airburst. No apparent damage on ground.
Table 5. Recorded sub-critical impacts of bodies with diameters of 10-50m
16
Table 6 shows the estimated effects of various sizes of impactor.
Yield Y
(MT)
<10
Interval
log T
101-102
3.0
75m
1.5
Irons make craters (Meteor Crater); Stones
produce airbursts (Tunguska). Land impacts
destroy area the size of a city (Washington,
London. Moscow).
102-103
3.6
160m
3
Irons and stones produce groundbursts; comets
produce airbursts. Ocean impacts produce
significant tsunamis. Land impacts destroy area
the size of large urban area (New York, Tokyo).
103-104
4.2
350m
6
Impacts on land produce craters; ocean-wide
tsunamis are produced by ocean impacts. Land
impacts destroy area the size of a small state
(Delaware, Estonia).
104-105
4.8
0.7km
12
Tsunamis reach hemispheric scales, exceed
damage from land impacts. Land impacts
destroy area the size of a moderate state
(Virginia, Taiwan).
105-106
5.4
1.7km
30
Land impacts raise enough dust to affect
climate, freeze crops. Ocean impacts generate
global scale tsunamis. Global destruction of
ozone. Land impacts destroy area the size of a
large state (California, France, Japan).
NEO
Diameter
Crater
D (km)
Consequences
Upper atmosphere detonation of stones and
comets; only irons (<3%) penetrate to surface
Table 6. Summary of impact effects as a function of energy.
Precise predictions of the positions and orbits of bodies in the solar system have been made, using
Newtonian principles, coupled where necessary with suitable relativistic modifications. Recent work
has shown that over long periods of time small uncertainties in the orbit or the dynamic model
eventually become significant, requiring regular monitoring of the discovered objects and continual
updating of their orbits. Where necessary, their predicted trajectories can then be revised. This
situation is particularly important for near-Earth objects that happen to pass close to a planet, in
particular the Earth, and should be considered the rule for cometary objects, whose orbits are known
to be subject to irregular non-gravitational perturbations due to outgassing, or effects due to the
physical fragmentation of the body.
17
9.
The Current Situation
_________________________________________________________________________________
Although the possibility that comets or asteroids could impact with the Earth was discussed as far
back as the late 17th century (by Sir Edmund Halley), and, since then, by others such as Harvey
Nininger in 1942 and Harold Urey in 1973, the scientific world's attention was really caught by the
publication, in 1980, of a paper entitled "Extraterrestrial Cause for the Cretaceous-Tertiary Extinction",
by Louis and Walter Alvarez of the University of California, Berkeley. The paper linked the sudden
extinction of about 70% of the recognised fossil species of maritime organisms, and possibly more
than 90% of all species on Earth, including the dinosaurs, with a major impact of a ten-kilometre
diameter body some sixty-five million years ago. Since then it has been determined that a 2-300
kilometre buried crater at Chicxulub in the Yucatan, Mexico, is the most likely "smoking gun".
Although Frank Dachille and Allan Kelly had suggested this theory in 1953 and M.W. De Laubenfels in
1956, the Alvarez work received the greatest prominence. Nine years later the close passage of
asteroid 1989 FC (now known as (4581) Asclepius) prompted a report from the American Institute of
Aeronautics and Astronautics (AIAA) which recommended an urgent increase in the detection rate of
potential impactors.
As a result of these events the United States House of Representatives charged the National
Aeronautics and Space Administration (NASA), in the NASA Multi Year Authorization Act of 1990,
with setting up two workshop studies, one "to define a program for dramatically increasing the
detection rate for Earth-orbit-crossing asteroids", and the other to "define systems and technologies to
alter the orbits of such asteroids or to destroy them if they should pose a danger to life on Earth". The
Detection Workshop (also known as the Morrison committee) report was finalised in January 1992,
and recommended that a survey for near-Earth objects be initiated as soon as possible. The
Interception Workshop reported in February 1993.
The plans for the Spaceguard Survey, which took its name from a similar project described by the
celebrated science fiction author Arthur C. Clarke in his novel "Rendezvous with Rama", called for the
establishment of a network of six 2.5 metre telescopes, positioned around the globe, and a central
research establishment. The estimated cost of setting up the project was, in 1993, $50 million, with an
additional $10 million per year running costs. The complete system of telescopes would take about
five years to build and bring on line.
In 1993 NASA allocated an extra $0.5 million for asteroid research. The United States Department of
Defense also allocated funds for a joint
DoD - NASA project to send a small
probe (Clementine) to survey the Lunar
surface, and visit (1620) Geographos, an
Earth crossing asteroid (sadly this part of
the mission failed). Clementine 2 is under
development, but the planned visits to two
asteroids have not received funding due
to the personal intervention of President
Clinton.
During 1993/94, several significant events
occurred
that
raised
public
and
professional awareness of the threat.
q
The much publicised impact of Comet
Shoemaker-Levy 9 on Jupiter in the
summer of 1994.
q
The "near-miss" of Asteroid 1994
XM1 in December 1994.
q
The publication of a position paper, entitled "Response to the Potential Threat of a Near-EarthObject Impact" by the AIAA in January 1995.
Figure 19 - The discovery plate of Asteroid 1994
XM1
18
The US Congress requested that NASA consider the threat with more urgency, and directed them to
work with the US Air Force (who already operate a network of telescopes used to track man made
satellites). The NEO Survey Science Working Group was established, under the chairmanship of
Eugene Shoemaker, and their report, published in June 1995, once again stressed the need for a
comprehensive survey of NEO's, and proposed a refined proposal for a project costing $24 million in
the first five years and $3.5 million annually for the following five years. These dramatically reduced
costs reflected the huge advances in telescope, sensor and data processing technologies. The report
dealt only with the US component, but endorsed the recommendations of the earlier Morrison
committee that international participation would be crucial. This is seen, not only as a way of
spreading the financial burden, or as a means of providing "all round" surveillance, but as an effort to
create a truly international forum for global defence. On 9 August 1995 NASA reported to Congress,
but announced that, due to financial constraints, it was unable to fully fund the SPACEGUARD
Survey. However, the agency stated that it remained committed to ongoing NEO survey activities, and
would be providing over $1 million per year for these efforts. With this level of researching, the survey
will take at least 100 years to catalogue 90% of potentially threatening objects.
The current situation is that, despite the urgency advocated by the scientists concerned, and some
politicians, very little is being done on national scales, except in the United States. Excellent results
are being produced by organisations such as the 0.91 metre "Spacewatch" telescope group operated
by a team under the leadership of Professor Tom Gehrels of the Lunar & Planetary Laboratory,
University of Arizona, and the Near
Earth Asteroid Tracker (NEAT)
programme, funded by USAF/JPL.
The third significant programme, the
Anglo-Australian Near-Earth Asteroid
Survey
(which
was
renamed
Spaceguard Australia in January
1996) ceased operation in December
1996 due to lack of funding. There are
a few others, but their surveys are
relatively small scale, and will take a
considerable
time
to
achieve
adequate coverage of the sky.
However, it is true to say that there is
rapidly increasing interest world-wide
amongst astronomers, both amateur
and
professional,
and
military
organisations.
On 20 March 1996 the Council of
Europe issued an advisory document
urging the participation of member
states and the European Space Agency (ESA) in the establishment of the "Spaceguard Foundation".
Figure 20 - Kitt Peak Observatory
19
10.
The Spaceguard Foundation
_________________________________________________________________________________
Commission 20 of the International Astronomical Union
(Positions and Motions of Asteroids, Comets and Satellites)
presented a resolution to the XX1st General Assembly in Buenos
Aires (1991. This Resolution called for the establishment of an ad
hoc Intermission Working Group, with the aim of investigating the
threat posed by NEO's and of facilitating a broad international
participation in the discussion.
The Working Group on Near-Earth Objects (WGNEO) produced
a report to the XXIInd IAU General Assembly in The Hague
(1994), in which it was recommended that the investigations and initiatives related to NEO studies be
put under the patronage of some international authority. The WGNEO then organised a workshop in
the island of Vulcano (Italy), in September 1995, with the title "Beginning the Spaceguard Survey".
The aim of the workshop was to emphasise the need for a co-ordinated effort, and to lay the
foundations for effective international co-operation on the subject. During an extended discussion of
the current situation, the participants in the Vulcano Workshop decided to set up the Spaceguard
Foundation, an organisation dedicated to sustaining and co-ordinating current research efforts worldwide. The aims of the Foundation are:
q
To promote and co-ordinate at an international level the discovery, follow-up and orbit
computation of NEO's;
q
To promote the study - from theoretical, observational and experimental points of view - of the
physico-mineralogical characteristics of minor bodies of the solar system, with particular attention
to NEO's;
q
To promote and co-ordinate a ground network (the Spaceguard System), possibly supported by a
satellite network, for continuing discovery observations and for astrometric and physical follow-up.
The Spaceguard Foundation was officially inaugurated on March 26, in Rome with the following
membership: R.P. Binzel (USA)
C. Blanco (Italy)
G.H. Canavan (USA)
M. Carpino (Italy)
A. Carusi (Italy)
C.R. Chapman (USA)
T. Gehrels (USA)
G.J. Hahn (Germany)
A.W. Harris (USA)
E.F. Helin (USA)
S. Isobe (Japan)
L.N. Johnson (USA)
C.-I. Lagerkvist (Sweden)
J.V. Lambert (USA)
B.G. Marsden (USA)
A. Maury (France)
A. Milani (Italy)
D. Morrison (USA)
K. Muinonen (Finland)
G. Neukum (Germany)
S.J. Ostro (USA)
P. Pravec (Czech Republic)
D.L. Rabinowitz (USA)
H. Rickman (Sweden)
H. Scholl (France)
P.K. Seidelmann (USA)
C.J. Shoemaker (USA)
E.M. Shoemaker (USA)
P. Sicoli (Italy)
A.G. Sokolsky (Russia)
D.I. Steel (Australia)
G. Tancredy (Uruguay)
P.D. Tennyson (USA)
R. West (Denmark)
G.V. Williams (USA)
I.P. Williams (UK)
D.K. Yeomans (USA)
A.L. Zaitsev (Russia)
This initiative has already received support from the Council of Europe, which has issued a document
encouraging member states to support the Foundation's efforts.
20
11.
Countermeasures
_________________________________________________________________________________
Studies have been conducted in both the United States and Russia on methods of avoiding potential
NEO impacts. There are two possible courses of action available once a threat has been identified:
11-1.
Destruction
The possibility of destroying potential impactors, probably with high yield nuclear weapons, has been
studied in some detail. With the current lack of detailed knowledge of the exact composition of
particular objects, and their structural strength, there is an element of doubt as to the effectiveness of
this course of action. The fear would be that incomplete disruption of the object would subject the
Earth to multiple impacts from pieces of the original body. The effects of transforming a cannon ball
into a cluster bomb could be more far-reaching than the original threat.
11-2.
Deflection
Figure 21 - A simple deflection scenario
Assuming that the potential impactor can be identified early enough, its orbit could be modified
sufficiently to ensure that an impact would not occur. The amount of modification required is inversely
proportional to the time available before impact, so early warning of a potential threat will be crucial.
Methods considered include the detonation of a nuclear weapon close to the body to change its orbit
or the use of propulsion units or mass drivers (using the material of the object itself as fuel) to
physically drive it from its path. Only very small adjustments would be required to ensure a miss rather
than a hit.
11-3.
The Deflection Dilemma
Any system designed to deflect an Earth threatening body from a collision course could also,
conceivably, be used to direct a non-threatening body towards the planet. This potential for misuse is
known as the "Deflection Dilemma".
21
12.
US Military Involvement
_________________________________________________________________________________
The primary arm of the US Forces concerned with space related matters is US Space Command
(SPACECOM). This is a unified command with three components: Army, Naval and Air Force Space
Commands. Air Force Space Command (AFSPC) already has a considerable surveillance capability
originally designed to track and catalogue man made space debris that could pose a risk to operations
in space. Optical and radar systems are both used for this purpose, along with associated
communications and data processing facilities. AFSPC is currently considering whether its suite of
sensors could, or should be improved and shared in the search for NEO's, and this evaluation is being
done at both policy and technical levels. The optical system deployed by AFSPC is a network of wide
field of view telescopes, known as Ground based Optical Deep Space Surveillance (GEODSS)
system. There is a programme to significantly upgrade the current vidicon detectors with CCD
sensors that will greatly enhance their capabilities. Access to the GEODSS network has been given to
researchers under a reciprocal agreement with NASA, and as a result of a Congressional directive.
Access to this technology has increased the NEO discovery rate significantly.
In May 1993 the Chief of Staff of the United States Air Force directed the Air University to undertake a
comprehensive study to identify capabilities, and supporting technologies, that the US would require
to preserve its national security in the year 2020. This became known as the SPACECAST 2020
study. One section of the report, entitled "Preparing for Planetary Defence: Detection and
Interception of Asteroids on Collision Course With Earth" clearly identifies the detection and
interception of NEO's as a military task that should be investigated now. SPACECAST 2020 was
followed up by the 2025 study that considered the subject of Planetary Defence in depth. The
conclusion of the 2025 study was clear and unequivocal - planetary defence is the responsibility of the
military establishment, and work should commence immediately, as a priority.
Despite the enthusiasm amongst serving officers in AFSPC, there is no reciprocal drive from the US
government. At the moment it would appear that Planetary Defence is not a popular subject, though
there is some support for the concept in Congress. However, apart from the NASA/AFSPC cooperation over projects such as NEAT and the Clementine spacecraft it seems unlikely that the US
military will become deeply involved in planetary defence under the present administration. Things
may change in the future.
Recent discussions with representatives of AFSPC have revealed that plans to upgrade the global
GEODSS system have been funded, making the whole network suitable for NEO search
programmes. Whether the instruments will be made available to astronomers remains in doubt, but
the potential will soon exist.
22
13. UK Military Involvement
_________________________________________________________________________________
The Government of the United Kingdom has been charged, by the Crown, with the defence of the
realm. This duty has been distilled into three National Defence Roles:
Defence Role 1 - To ensure the protection and security of the United Kingdom and its dependent
territories, even when there is no immediate external threat.
Defence Role 2 - To ensure against any major external threat to the United Kingdom and its allies.
Defence Role 3 - To contribute to promoting the United Kingdom's wider security interests through
the maintenance of international peace and security.
It should be noted that there is no definition or limitation on possible threats to the United Kingdom
explicit in these tasks. The Ministry of Defence has stated that they do nor regard planetary defence
as a role for the UK military establishment, and no action will be taken in the forseeable future.
However, should a major impact occur anywhere in the world there are a number of reasons that will
compel the Ministry of Defence to involve itself:
13-1.
The Resulting Need For Humanitarian Relief.
The MoD will certainly be involved in any humanitarian relief effort after such a disaster.
Humanitarian relief efforts have become a significant mission for UK forces, with many examples
during the last few years, not only in the UK, but also wherever it might be needed in the world.
Previous and current operations will be minor efforts compared to what might be needed in response
to even a relatively small impact if it occurred in a populated area. This might require a concerted
effort from many nations and place a severe strain on the resources of the international community
even if everyone was co-operative.
13-2.
The Possible Destabilisation Of The International Community.
A natural disaster as catastrophic as a moderate or major impact would put tremendous pressure on
the nations involved, both friend and foe, destabilising not only their economic but social fabric.
Indeed, such a calamity will affect the entire world community. Governments have lost stability to
lesser disasters when they found their resources lacking to adequately respond to the needs of its
victims. Often it has only been the infusion of external aid that has prevented severe consequences.
These consequences when a significant portion, perhaps as much as 25 percent, of the world's
population is in need of aid, hardly bear contemplation, particularly when the duration of the effects is
unknown.
13-3.
The Possible Threat To National Security.
Given an impact event, the effects could very well threaten the national security of the UK, even if it
were not physically affected by the initial effects. The devastating effects to government and social
structures will be equivalent to those predicted for a post-global-nuclear war holocaust, but worse.
13-4.
The Inevitable Nation-Wide Calls For Action.
Were a threatening body to be detected in advance, the nation and perhaps the entire planet will quite
naturally look to the military establishment for the fortitude, technical expertise and leadership, not to
mention the required force in the form of nuclear devices, to counter such a threat to its citizen's lives
and well being. Other national organisations and agencies will certainly be involved, including Atomic
Weapons Establishment, the Departments of Trade and the Environment, the Home Office, and the
Foreign and Commonwealth Office. There will have to be an international effort. However, few
organisations other than the military forces of the world have the experience and wherewithal to even
attempt such an effort. The US and Russian military and space infrastructures are probably the only
viable capabilities equal to the task of mitigation, but such a project would have to be international in
scope, given the common threat and the span of global expertise.
23
14.
International Co-Operation
_________________________________________________________________________________
Traditionally the detection of asteroids and comets has always been an international effort. By its very
nature, any large-scale Planetary Defence programme will have to be international in scope. Current
and planned international participation includes:
q
In China, funds have been allocated for a dedicated one-metre telescope.
q
European Southern Observatory, with its headquarters in Munich, and telescopes in Chile.
q
The Institute for Theoretical Astronomy, St. Petersburg, Russia.
q
In the United States, NASA announced, in April 1998, a doubling of their expenditure on NEO
studies, from $1.5 million to $3 million per year.
q
The Near Earth Asteroid Tracking system (NASA/JPL).
q
The Smithsonian Astrophysical Observatory, Cambridge, Massachusetts.
q
The Spacewatch Telescope, University
of Arizona.
q
The NEAT programme has been in
operation since 1995, utilising a USAF
1-metre GEODSS telescope.
q
LINEAR is another GEODSS system
located in New Mexico..
q
LONEOS uses a 0.6 metre Schmidt
near Flagstaff.
q
There
are
other,
smaller
US
programmes in operation, including
Catalina, Bigelow and TASS.
Figure 22 - The NEAT CCD System
q
In Japan there is a follow-up programme using the Kiso Schmidt telescope. In April 1998, a major
new surveillance programme was announced. 2 billion yen will be spent on a radar telescope and
a 1-metre optical telescope for NEO and space debris studies.
q
In Italy, there will soon be a search and follow-up programme, using a 1-metre reflector closely
modelled on the Spacewatch programme.
q
In France, the OCA Schmidt is being fitted with a new CCD system in collaboration with DLR
Berlin.
q
In Sweden, there are plans for a 2.7 metre Spaceguard telescope in the Canaries.
q
Finland is planning a large telescope in Namibia.
q
Argentina, Uruguay and Brazil plan to collaborate over two 1-metre telescopes to be located in
western Argentina.
The United Kingdom has a significant tradition in the field of planetary and cometary science that is
recognised world-wide. Many British institutions are at the cutting edge of Solar System studies, and
there is a generation of distinguished astrophysicists who have encouraged UK scientific work in this
field, including Professor Sir William McCrea, Professor Sir Bernard Lovell, Professor Sir Fred Hoyle
and the late Dr Ernst Opik whose pioneering work on cometary catastrophism was at the forefront in
the early decades of NASA.
24
15.
Programme Spin-Offs
_________________________________________________________________________________
15-1.
Scientific
A comprehensive programme aimed at the study of the origins, orbits and compositions of asteroids
and comets would have enormous impact on the scientific community. These bodies represent the
primordial material from which the solar system formed some 4,500 million years ago, and their
analysis would be invaluable to studies of the formation and early evolution of the solar system, and to
the search for similar systems around nearby stars. There are also likely to be significant opportunities
for sensor development, particularly in the optical and infrared wavebands.
15-2.
Commercial
Given the composition of asteroids and comets it is likely, in the future, that there will be considerable
commercial interest in them. The mining of minerals, metals hydrocarbons and, significantly, water for
use in the exploitation of space could become viable, reducing the requirement to lift such materials
from Earth's gravity well (the most expensive and energy intensive part of any space project). Once
non-threatening techniques have been developed, the deflection of NEO's into convenient orbits, and
the subsequent mining of their resources could become the province of commercial organisations.
Clearly, there would have to be strict controls applied, to prevent the use of such technologies to
direct non-threatening bodies into Earth crossing orbits, but such problems are not insoluble.
15-3.
Intangible
By its very nature, the establishment of a global survey for NEO's, and research into suitable
deflection methods must be an international undertaking. The co-operation of nations to counter a
global threat can only contribute to the larger international co-operative effort that is a feature of
current world affairs. Concentration on a threat to the entire biosphere may divert national or individual
perspectives from more traditional internecine squabbles.
Figure 23 - Our home - the Earth-Moon system from the Galileo Spacecraft
25
16.
Financial Considerations
_________________________________________________________________________________
In 1994 the NASA sponsored NEO Detection Workshop, chaired by Dr. Eugene Shoemaker
recommended the establishment of a global surveillance network consisting of six ground based
telescopes linked to a data collection centre. The estimated cost amounted to $50 million to establish
the system, and $10 per year to run. These costs are now regarded as being on the low side, but,
with advancing technology, not wildly unrealistic. A recent estimate for the construction of a dedicated
telescope (as described later) was in the region of £ 5 million. The UK could reasonably be expected
to contribute one of the six instruments required for the global network at a similar cost. Such a
project, including running costs, would cost less than £ 10 million for a ten-year programme.
A globally threatening impact can reasonably be expected every 100,000 years. Such an event will
kill at least a quarter of the world's human population. The British government values a human life at
£ 820,000 ( the Department of Transport figure), so the value of 25% of the population is about 12.5
million times £820,000. The resulting figure, divided by the expected time interval between events
equals the actuarial annual cost to the United Kingdom, and is equivalent to £123 million per year.
£ 123 million per year therefore represents the probable cost of doing nothing, but only includes the
cost of "lives", disregarding property and heritage losses. In addition, this calculation does not include
the costs incurred by the impacts of smaller, more common bolides (see Figure 1).
In the United Kingdom the government has spent some £ 600 million to increase the statistical interval
between "significant events" at the Sizewell B nuclear installation from 105 years to 107 years. A
"significant event" in this context would result in a few hundred or, at worst, a few thousand fatal
casualties. A globally threatening impact event, killing 25% of the world' s population can be expected
on time scales two orders of magnitude less than this.
The Millennium Dome is costing the tax-payer £ 758 million.
The Albert Memorial cost £ 11 million to restore.
26
17.
If it' s so important, why is so little being done?
_________________________________________________________________________________
17-1.
No one realised that there was a problem.
Appreciation of the threat posed to the ecosphere by asteroids and comets has only come to
prominence in the past decade or so. The evidence of cosmic impacts has been in plain view since
the invention of the telescope, but the scale of planetary bombardment has only become clear since
the advent of the space age. A number of events have occurred in the past few years, such as the
discovery of the probable K-T "smoking gun" at Chicxulub and the collisions of Comet ShoemakerLevy 9 on Jupiter, that have brought the subject to the world's attention. Past prejudice against
catastrophist notions is lessening as the evidence builds up, and the reality of major impacts is no
longer in doubt.
17-2.
Historical Inertia.
Ancient man was quite convinced that cosmic influences had a
significant part to play in his way of life and continued well being.
This conviction is clearly demonstrated in the stories and myths
from around the world concerning conflict and disaster meted out
from the skies, usually by omnipotent "gods". This catastrophist
view of the cosmos reigned supreme until the Age of Reason
when Newtonian principles turned the unknown and unpredictable
universe into a benign, mechanical system and Darwinism
spawned the concept of gradual evolution over extended periods
of time. In the resulting predictable, gradualist cosmos there was
no place for catastrophism or major, sudden changes in the global
environment. Since the late 1980's the realisation that Darwinian
evolution has almost certainly been punctuated by massive
catastrophic events, causing major redirection in biological and
geographic evolution has led to the breaking of many scientific
paradigms. The move from gradualism towards catastrophism is
causing a major rethink of many cherished ideas.
17-3.
Figure 24
Nothing can be done about the problem, so why bother?
Until the dawn of the space age mankind was truly helpless in the face of cosmic bombardment, so
there was little to be gained from worrying about the problem. However, the advances in technology
that have occurred during the past two decades or so have changed the situation radically.
Surveillance technology now allows the detection and tracking of threat objects, while spacecraft
technology has advanced sufficiently to allow the interception of such bodies. Much of this has been
as a result of the United States' Strategic Defence Initiative, or "Star Wars" programme. Measures to
deflect threatening bodies have been developed, involving the use of nuclear weapons, but emerging
technologies may provide more "environmentally friendly" alternatives. The problem can be dealt with
now, albeit in a fairly crude fashion.
17-4.
Money.
NEO surveillance, tracking and mitigation programmes cost money. While the first two are relatively
cheap, any expenditure needs detailed and credible justification in these days of fiscal stringency. The
threat to humankind from asteroidal or cometary impact is not high enough on anybody's priority list
for the required funding. In part, this is due to a lack of knowledge relating to the threat, and, in part to
the perception that other contingencies are more important..
17-5.
Self interest.
The blame for inaction cannot be placed exclusively at the door of the politicians. Within the scientific
community there is still disagreement, some acrimonious, over the nature and extent of the threat. It is
perfectly natural for scientists to disagree, indeed that is the nature of the scientific method. However,
few would dispute at least the possibility of a significant threat, and, given the possible consequences,
27
it is not justifiable to oppose programmes to assess that possibility. That would be playing dice with
the survival of the human species. Many scientific bodies oppose research into the NEO threat on the
grounds that such programmes might divert funding from their particular fields. While this is perfectly
understandable from a narrow perspective, it is an abrogation of the responsibility of science to
safeguard humankind, or at least to alert it to threats to its well being.
17-6.
Responsibility.
The evidence for past catastrophic events, and the inevitability of a reoccurrence is incontrovertible,
but exactly who should be responsible for doing anything about it? Planetary Defence is a multidisciplinary undertaking. Astronomers have been at the forefront of the search for, and detection of
NEO's, but planetary scientists, geologists, palaeontologists, biologists, physicists and many others
have been deeply involved in piecing together the jigsaw that has resulted in our current state of
knowledge. But is the problem strictly scientific? Scientists are concerned with the acquisition and
interpretation of new data. To study asteroids and comets the researcher needs to study only a
representative sample; there is no need to find them all. A planetary defence programme would have
to do so. The funding and resources required to detect and track all NEO's cannot therefore be
justified on scientific research grounds. Defence is usually the prerogative of the military, but there is
some resistance from the defence establishment to becoming involved in planetary defence. The one
notable exception is in the United States where the US Air Force has been given the task of coordinating planetary defence efforts. The normal reasons for inaction invoke the inability of a single
nation to achieve very much, though this ignores the essentially international nature of planetary
defence. The weak excuses hide the real reason - money. Defence budgets are stretched to the limit
without having a new drain on already scarce resources. So, neither the scientific or military
communities are willing to take responsibility for planetary defence. Governments will have to come to
some decision sooner or later, preferably before the event.
28
18.
Spaceguard UK
_________________________________________________________________________________
18-1
Aims
Spaceguard UK was established at the beginning of
1997 to pursue the following aims:
q
To promote and encourage British activities
involving the discovery and follow-up observations
of Near Earth Objects.
q
To promote the study of the physical and dynamic
properties of asteroids and comets, with particular
emphasis on Near Earth Objects.
q
To promote the establishment of an international,
ground based surveillance network (the Spaceguard Project) for the discovery, observation and
follow-up study of Near Earth Objects.
q
To provide a national United Kingdom information service to raise public awareness of the Near
Earth Object threat, and technology available to predict and avoid dangerous impacts.
18-2
Affiliation
Spaceguard UK is affiliated with the international Spaceguard Foundation. The Aims of
Spaceguard UK are fully harmonised with those of the Foundation. The activities of Spaceguard UK
are intended in no way to detract from those of the Foundation; they are intended to support and
complement them, with a specific bias towards the situation as it pertains to the United Kingdom.
Details of the Spaceguard Foundation, its aims, by-laws and membership can be obtained from The
Spaceguard Foundation or from Spaceguard UK.
18-3
Activities
Members of Spaceguard UK have already been active in promoting the assessment of the United
Kingdom’s contribution to the international NEO detection effort. A number of well-publicised meetings
have been precipitated by the activities of Spaceguard UK, taking the subject of Planetary Defence
from the realm of a handful of experts to the corridors of the House of Commons and the British
media. Spaceguard UK is acknowledged as the prime UK non-governmental organisation concerned
with Planetary Defence and the impact threat, and is the most influential body of its type in the
country.
As a result of the actions of Spaceguard UK, on 12th November 1996 the British National Space
Centre hosted a meeting to bring together as many interested parties as possible to assess exactly
what the United Kingdom is doing in the field, and to discuss what should be done in the future. The
meeting was exceptionally well attended with representatives of the following organisations
contributing:
q
q
q
q
q
q
q
q
q
q
q
q
The Royal Greenwich Observatory
The Armagh Observatory
AWE Aldermaston
The Defence Research Agency
The Spaceguard Foundation
The University of Kent
The British National Space Centre
The Natural History Museum
The Foreign and Commonwealth Office
Spaceguard UK
The Particle Physics and Astronomical Research Council
The Ministry of Defence
29
Much of the meeting was spent reviewing British research programmes that are dealing with related
subjects, including studies into man made space debris, the Tunguska event, current and future
space missions and risk assessment. It quickly became clear that the UK has very significant
intellectual and physical resources that could make an enormous contribution to any international
effort to mitigate the risk from NEO' s. Dr Jasper Wall, the Director of the Royal Greenwich
Observatory, summed up the conclusions:
q
There was unanimous agreement that the threat exists, and is significant enough to warrant
further investigation.
q
There is a requirement for a Working Group to assess the UK contribution to international efforts,
and how this could be co-ordinated with international bodies.
q
There is a requirement for a multi-disciplinary group to study the threat, especially those aspects
of a non-astronomical nature.
q
Funding must be sought from national and international sources.
q
There is a need to raise public understanding of the issues, and confidence that they are being
addressed.
These agreements represent a significant step towards the establishment of a co-ordinated UK
response to the threat, within the framework of international efforts. Despite these results, the Under
Secretary of State for Science and Technology has decided that the United Kingdom will not fund
additional studies into the threat from NEO' s, or Planetary Defence matters over and above the
national contribution to ESA which is, in turn, providing a modest grant to the Spaceguard Foundation.
A second meeting, with much wider participation was held in July 1997 at the Royal Greenwich
Observatory, Cambridge. A lot of ground was covered, but Dr Nigel Holloway, a risk analyst, made
one of the most significant comments in his paper:
“The risks from intermediate and large NEO impacts, associated with tsunami and impact winter
effects respectively, fall close to the UK national limits of tolerability, without regard for the fact that the
overall risks to the world are a hundred times higher again. Were the risks "owned" then the owner
would be put under strong pressure to reduce the risk, even at considerable expense. By comparing
other risk management expenditure decisions, the NEO risk is found to be sufficient in magnitude to
warrant substantial action. Astronomers should consider the relative importance of NEO detection and
their other projects in this light. It is some time since astronomers have been called upon to serve in a
directly useful fashion at the expense of their more theoretical aspirations. The discovery of the NEO
risk changes that.”
In addition, the meeting agreed that Spaceguard UK should become the prime non-governmental
organisation concerned with the impact threat in the United Kingdom, and endorsed the Spaceguard
UK Action Plan as the way ahead.
Current activities are concentrated on ensuring that the consensus achieved at the meetings of the
UK NEO Working Group is transformed into meaningful action by the British government and
organisations world-wide. This will be achieved through continued co-operation with relevant national
and international institutions, an active and ongoing press campaign and the dissemination of
information to the general public by physical and electronic means. In addition, Spaceguard UK is
developing a sensible and feasible action plan for the development of a UK project to detect and study
potentially threatening near Earth objects, as part of the growing international programme.
Over the past eighteen months, members of Spaceguard UK have been involved in over a dozen
television appearances, six radio broadcasts, and have had more than twenty articles published in
popular and professional journals. In addition, nine public lectures have been delivered country-wide,
and more are in preparation. A quarterly publication, IMPACT, containing news and articles of
interest is distributed to all members.
30
18-4
q
Membership
Patrons
Patrons are those individuals who have made outstanding contributions in the field of NEO studies, or
who have special qualifications that enable them to significantly further the aims of Spaceguard UK.
Sir Bernard Lovell, Sir Crispin Tickell, Sir Arthur C. Clarke and Dr Patrick Moore are Patrons.
q
Associate Membership
Associate Members are those currently involved in activities or studies related to Planetary Defence,
and who form a core of multi-disciplinary expertise in the subject. Associate membership includes:
Dr David Asher
Professor M E Bailey
Dr M Baillie
Dr Sue Bowler
Dr S V M Clube
Simon Clucas
Dr Matthew Genge
Dr Monica Grady
Dr Simon Green
Dr M Grady
Peter Grego
Dr John Gribbin
Dr N J Holloway
Dr. David W. Hughes
Dr Ian Lyon
Professor J A M McDonnell
Dr Brian Marsden
q
Dr Michael Martin-Smith
Robert Matthews
Dr Jacqueline Mitton
Dr W M Napier
Dr B J Peiser
Mr. Nick Pope
Dr P Roche
Dr J E Salt
Robin Scagell
Peter Snow
Dr D Steel
Professor Jasper Wall
Professor Chandra Wickramasinghe
Dr Gareth Williams
Professor I P Williams
Jerry Workman
Dr J Zarnecki
Visiting Membership
Visiting Members are those currently involved in activities or studies related to the NEO Impact
Threat, or who have made outstanding contributions in the field of NEO studies but who are not British
nationals. Visiting Membership includes:
Dr Mike A'Hearn
Dr Walter Alvarez
Dave Balam
Professor Richard Binzel
Peter Brown
Dr Greg Canavan
Dr Nikolaj Chernykh
Dr Paul Chodas
Dr Paolo Farinella
Dr Andrea Carusi
Dr Tom Gehrels
Dr Mayo Greenberg
Maj Wynn Greene
Dr Gehard Hahn
Dr Alan W. Harris
Dr Scott Hudson
Dr Eleanor Helin
Lt Col Lindley Johnson
Dr Syuzo Isobe
Bob Kobres
Dr Steve Larson
q
David Levy
Dr Alain Maury
Dr Robert McMillan
Dr Andrea Milani
Dr Karri Muinonen
Professor W Mullen
Dr Steven Ostro
Dr Steven Pravdo
Dr Petr Pravec
Dr David Rabinowitz
Dr Hans Rickman
Dr Joel Schiff
Dr. Ken Seidelmann
Dr Carolyn Shoemaker
Dr Viktor Shor
Dr Milos Tichy
Dr Jana Ticha
Dr G. Verschuur
Colonel S.P Worden
Dr Don Yeomans
Dr. Jin Zhu
General Membership
General Membership is open to any individual with an interest in the subject of the NEO Impact
Threat. There are currently over 120 General members.
q
Corporate Membership
Corporate Membership is open to those organisations or societies that share the aims of Spaceguard
UK.
31
19.
Spaceguard UK Proposal
_________________________________________________________________________________
19-1.
Introduction
Any project to detect, follow-up and/or determine the physical properties of NEOs must be coordinated with other national and international programmes. The threat is global, therefore the
solution must also be global. In addition, there are good practical reasons for a global programme.
Before any such project can have any chance of success, a programme of public education must be
undertaken to heighten awareness of the need for it in the first place. Spaceguard UK has been
conducting such a campaign for the past two years, and is continuing to do so.
While Spaceguard UK has, so far, had no practical involvement in specific NEO search or follow-up
projects, we have been incidentally campaigning for the modification of the UK Schmidt Telescope
(UKST) to be used in such a role. This project was viable as the UKST was due for decommissioning.
However, it has recently become clear that the UK UKST has been "reprieved" and is going to be
fitted with a new Multi-Object Spectrograph, called 6dF. It is possible that this will preclude the
possibility of using the UKST as part of the global NEO detection network the next three to five years.
However, it would be quite possible to dual-task the telescope as has been done in the past. As well
as its photographic work the UK Schmidt Telescope has been fitted with a multi object spectroscopy
system known as FLAIR (Fibre-Linked Array Image Reformatter), and programmes have been run on
a time-sharing basis. It would be possible for the 6dF project to run concurrently with a CCD-based
NEO survey, but it is prudent to consider alternative UK contributions to the international effort.
19-2.
The Requirement
A number of comprehensive and well-documented studies have already been undertaken, mainly in
the USA, to determine the requirements for detection and follow-up programmes. A representative list
of references can be found at Annex A. There is global consensus over the general accuracy of these
studies, though there is still some controversy over the precise nature of the threat. The global NEO
community generally accepts the requirements described therein. There is, therefore, no necessity to
repeat work that has already been completed. The requirements are clear, well documented and
agreed internationally, so further study would be a duplication of effort and a waste of resources. Any
objections to the need for such a programme will be found to stem largely from reasons other than
scientific analysis of available data, and should not be allowed to divert attention and resources from
the real work.
19-3.
Priorities
The priorities for any international Spaceguard project must be:
q
One - Detection and cataloguing of all NEOs larger than one kilometre in diameter, (the NASA
target is for this to be accomplished within 10 years, but, with current resources the project will
take in excess of 50 years), and identification of any potential hazards.
q
Two - Follow-up astrometric observations to secure their orbits and allow the prediction of
possible future impacts.
q
Three - Physical studies of asteroids and comets to ascertain their broad compositional and
physical characteristics in case direct intervention might become necessary.
19-4.
Deductions
q
The only way to achieve priorities one and two is to conduct an observational programme.
Without the data resulting from such a programme priority three cannot proceed. Therefore, at
this stage, an observational project should be the first priority for Spaceguard UK.
q
The requirements for such a programme are well documented, and undisputed.
32
q
The necessary trained personnel to design, build and operate the required instrumentation exist,
but unless their expertise is used, this resource will soon be lost.
q
The sole limiting factor is funding.
19-5.
Scientific Case
The detailed physical and chemical composition of NEOs that pass close to Earth and are relatively
easy targets for ground-based observations and space missions provides important information on the
primordial material that built the planets. Studies of the main asteroid belt have produced new insights
into its dynamical and collisional evolution, and have shown in particular that the main belt is a
significant source of observed NEOs. Moreover, the number of known low-activity comets is steadily
increasing, leading to new estimates of the number of such bodies and of their relationship to
asteroids. The discovery of large comets or asteroids in the Edgeworth-Kuiper belt beyond Neptune
and of the Centaur population (between Saturn and Neptune) has also opened up a whole new area
of investigation, allowing the remnants of the Sun's own proto-planetary disc to be studied.
The processes by which Near-Earth Objects are produced from storage in the main belt, the
Edgeworth-Kuiper belt or the Oort cloud are complex, involving fundamental aspects of their dynamics
and detailed physical and collisional modelling. Such studies play a key role in theories of the origin of
the solar system and of the formation and evolution of the Earth and other planets. An understanding
of the latter is a prerequisite to developing a coherent understanding of newly discovered planetary
systems around other stars.
Figure 25 - Deep Space 1
These rapid developments in solar system astronomy are observationally driven, and have arisen
against a background of unprecedented activity in space science (missions such as Galileo, NEAR,
Clementine 2 (currently on hold), Rosetta, Stardust, Deep Space 1, Deep Space 4), the passage of
recent, bright comets (Hyakutake, Hale-Bopp), a significant increase in NEO discoveries, and growing
public and international concern about the possible impact threat to the biosphere. Nevertheless,
progress up to now has been painstakingly slow, relying on the study of a handful of objects at a time
and often taking years to produce significant results. A dedicated 2.5 metre telescope would produce
a significant increase in the number of objects available for study.
The scientific community has a responsibility and duty to those whose who finance its activities to
address subjects of current interest and concern. Research into small solar bodies provides ground
33
truth for an assessment of the impact hazard to civilisation, at the same time provides fundamental
results on the origin and evolution of the solar system. The research is timely and should be given
high priority. Moreover, the planetary science community in the UK is uniquely placed in terms of its
interests and expertise to make significant contributions to the field.
19-6.
The UK NEO Research Community
There is wide and increasing interest in this area of research, especially at Armagh, Queen’s
University Belfast, Queen Mary and Westfield College, University of Kent Canterbury, Sheffield
University, and in comparative planetology at the Open University, Manchester, the Natural History
Museum, Lancaster and University College London.
The UK community has a strong tradition in both the theory and observation of small solar system
bodies, and maintains a highly successful international profile in both areas.
19-7.
Possible International Partnerships
UK astronomers and Spaceguard UK have many international links. EU network collaborators and
others include groups with specific interests in observational and dynamical studies. These include:
German Space Institute Berlin (Neukum, Hahn, Harris)
University of Helsinki, Finland (Muinonen)
University of Namur, Belgium (Henrard)
Observatoire de la Cote d'Azur, France (Scholl, Froeschle,
Maury)
University of Pisa, Italy (Farinella, Milani)
University of Thessaloniki, Greece (Hadjidemetriou)
University Torino, Italy (Zappala, Cellino)
University of Uppsala, Sweden (Rickman, Lagerkvist).
In addition, Spaceguard UK has links with organisations such as:
The Spaceguard Foundation, (Carusi, Marsden)
Spacewatch (Gehrels, Scotti, McMillan)
Instituto di Astrofisica Spaziale, Rome (Carusi,)
The Japanese NAO/Kiso Schmidt (Isobe)
Lowell Observatory (Bowell),
The IAU MPC (Marsden, Williams)
Spaceguard Australia
Spaceguard Canada
Spaceguard Japan
Spaceguard Germany
Spaceguard Croatia
Relevant US DoD (AFSPC) staff.
Jet Propulsion Laboratory (Helin, Rabinowitz, Harris,
Chodas, Pravdo, Yeomans)
US Naval Observatory (Seidelmann)
University of Northern Arizona (Shoemaker)
Armagh Observatory (Bailey, Napier, Asher)
Crimean Astrophysical Observatory (Chernykh)
University of Western Ontario (Brown)
University of Maryland (A'Hearn)
Massachusetts Institute of Technology (Binzel)
University of Victoria (Balam)
University of California (Alvarez)
Klet Observatory (Ticha)
Institute of Applied Astronomy of RAS (Shor)
Los Alamos National Laboratory (Canavan)
University of Arizona (Larson, McMillan)
British National Space Centre (Tremayne-Smith)
European Space Agency
Leicester University
Liverpool John Moores University (Peiser)
University of Kent Canterbury (Zarnecki)
Salford University (Tickell)
The Open University
Queen's University Belfast (Baillie, Fitzsimmons)
International collaboration enhances the expertise available to researchers, and would provide
additional theoretical and observational input to the project.
19-8.
Options Open
The options open to Spaceguard UK are:
1.
Build, or participate in the building and operating of a new, dedicated search and follow-up
telescope.
2.
Find an existing, available telescope suitable for use in a detection and follow-up programme.
3.
Establish a National Spaceguard Centre to study the NEO threat, and to develop future plans.
It could also conduct "precovery" searches, using the UKST Plate Library at the Royal
Observatory Edinburgh (ROE).
4.
Establish an amateur network for follow-up observation.
34
The effectiveness of professional programmes will be proportional to their costs - you get what you
pay for.
19-9.
Project Personnel
For optimum performance and cost-effectiveness dedicated, professional personnel must staff any
project resulting from this proposal. It is suggested that advice be taken from academia and the
relevant research councils over suitable individuals, salary levels and personnel administration. To
achieve the required level of co-operation from these bodies ring-fenced funding must be available,
and a credible project must be offered. The latter is the subject of this proposal, while the acquisition
of former is the aim of the same.
19-10. Option 1 - Build a New, Dedicated Search and Follow-Up Telescope.
General
Without doubt, to build a new 2.5-metre telescope, with the associated infrastructure is the "RollsRoyce" option, and would be the most expensive option. However, a project such as this could be
undertaken in collaboration with commercial interests, other nations or organisations such as The
Spaceguard Foundation who already have plans
for a search telescope in Namibia.
Development and building costs will be
substantial, and in addition to the capital costs,
running costs would have to be factored into the
budget. However, the advantages of a purposebuilt instrument, operating in the most
advantageous location (possibly the Canary
Islands) are considerable. There would be no
conflicts of interest, and observing time would be
guaranteed. There may also be possibilities for
other research projects, using the instrument.
This option will entirely depend on adequate
funding being obtained from private and
commercial sources.
Advantages
1.
A
dedicated
facility
uninterrupted observation (the
capable of this).
Figure 26
will
only
2.
A 2.5 metre telescope will be able to
detect faint, distant or small NEOs, giving
adequate warning time for the development of
mitigation strategies.
3.
Both detection and follow-up programmes could be conducted without distraction.
4.
Funding will be ring-fenced, and not liable to diversion.
Disadvantages
1.
Cost. Initial costs will be high, and running costs will be higher than for other options.
Project Phases
q
Phase 1 - Groundwork
allow
facility
Year 0 - 0.5
35
Initial team selection
Feasibility Study
Initial sponsorship trawl.
q
Phase 2 - Preparation
Year 0.5 - 1
Compilation of a business plan.
Co-ordination with the Spaceguard Foundation
Initial design and costing of the Spaceguard Telescope.
Site selection
Personnel selection
Costing of necessary infrastructure.
q
Phase 3 - Funding and Support
Year 1 - 2
Search for sponsorship.
Lobbying of national and international organisations for funding and support. (Commercial interests,
the International Astronomical Union (IAU), NASA, the United Nations, the Department of Trade and
Industry (DTI), the British National Space Centre (BNSC), the Particle Physics and Astronomical
Research Council (PPARC), academia)
q
Phase 4 - Development
Year 2 - 3.5
Hardware and software development
Establishment of link with MPC
Site preparation
Personnel training
q
Phase 5 - Construction
Year 3.5 - 4.5
Construction of necessary infrastructure
Telescope construction
Personnel training (continues)
q
Phase 6 - Trials and Testing
Year 4.5 - 5.5
Initial operations, trials and testing
Hardware testing and integration
Software validation
System integration
q
Phase 7 - Operations
Year 5.5 ->
Operations
Upgrades
Costs
Capital costs
Primary Mirror 2.5 m, f/2.5
Corrector Plate
Tube and Structure (Alt-Az)
Dome
CCD array, processor
Running and maintenance costs
£ 800,000
£ 150,000
£ 1,500,000
£ 500,000
£ 2,000,000
£ 450,000 pa
The total cost of a ten-year programme would therefore be £ 9,450,000
36
19-11. OPTION 2 - Find an Existing Telescope Suitable for Use in a Detection and Follow-Up
Programme.
General
There are a number of possibilities here. At Herstmonceux there is a 24" Hewitt Schmidt camera. It
would be possible to modify this instrument to use as an Automatic Patrol Telescope; a similar
concept to the Baker-Nunn instrument developed by the University of New South Wales. A twin
instrument is currently located at the Anglo-Australian Observatory (AAO) at Siding Spring. The
telescope is unused, and the AAO would like it removed. A collaborative project with Australian
interests may be possible, using the Herstmonceux instrument as a hardware and software test-bed,
and the AAO instrument for active observation.
Given the likely time-line for Option 1, it may be feasible to consider the use of the UKST again. It is
possible that the 6dF project will be complete before Spaceguard is ready for system integration, or
that dual tasking of the UKST might be possible.
It is impossible at this stage to estimate the costs involved in the re-roling of any available instruments
(other than the UKST), but they are certain to be less than those are for Option 1.
Advantages
1.
Costs will be significantly lower than those for Option 1.
2.
The 24" Hewitt camera, suitably equipped with a CCD mosaic, will have a sufficiently wide
field of view and limiting magnitude to make a significant contribution to the global detection
programme.
3.
Hardware and software development could be undertaken using the Hewitt camera at
Herstmonceux. The AAO Hewitt is well located for detection and especially follow-up observing in the
Southern Hemisphere.
4.
International co-operation between Spaceguard UK and Australian interests would reflect the
international nature of the Spaceguard project.
5.
Should it become available, the UKST would be an excellent detection system, outperforming
any current instrument in the world.
Disadvantages
1.
The 24" Hewitt has too small an aperture to detect the smaller, fainter NEOs that have a
relatively high probability of impact. It will also lack the ability to detect larger NEOs at extended
ranges. It is an antiquated system that might prove to be unsuitable.
2.
Running costs will not be significantly lower than those for Option 1.
3.
The UKST might not be available for 3 to 5 years.
Project Phases
q
Phase 1 - Groundwork
Year 0 - 0.5
Initial team selection
Feasibility Study
Initial sponsorship trawl.
q
Phase 2 - Preparation
Compilation of a business plan.
Co-ordination with the AAO
Year 0.5 - 1
37
Initial design and costing of the CCD system.
Personnel Selection
Costing of necessary support resources (IT, Communications).
q
Phase 3 - Funding and Support
Year 1 - 2
Search for sponsorship.
Lobbying of national and international organisations for funding and support. (Commercial interests,
IAU, NASA, UN, DTI, BNSC, PPARC, academia)
q
Phase 4 - Development
Year 2 - 3.5
Hardware and software development
Establishment of link with MPC
Personnel training
q
Phase 5 - Trials and Testing
Year 3.5 - 4
Initial operations, trials and testing
Hardware testing and integration
Software validation
System integration
q
Phase 6 - Operations
Year 4 ->
Operations
Upgrades
Costs
Costing for the modifications to the Herstmonceux Hewitt Schmidt are ongoing, but are likely to be in
the region of:
Capital costs (CCD array, processor)
Capital costs (Field Corrector)
Running and maintenance costs
£ 15,000
£?
£ 200,000 pa
The total cost of a ten-year programme with the Hewitt Schmidt would therefore be £ 2,115,000, plus
the cost of a field corrector.
Costing for the modification and operation of the UKST are as follows:
Capital costs (CCD array, processor)
Running and maintenance costs
£ 2 million
£450,000 pa
To conduct a comprehensive ten-year programme with the UKST would cost £ 6,500,000. The
results from the latter would, however, be significantly better than the former, outperforming any other
detection programme in the world.
19-12. OPTION 3 - Establish a National Spaceguard Centre to Study NEOs, and to Conduct
"Precovery" Searches, Using the UKST Plate Library at ROE.
General
There is an essential requirement to study of the physical and dynamic properties of asteroids and
comets, with particular emphasis on NEOs. There is already substantial work being done in this field
in the UK, but the creation of a study team dedicated to the investigation of NEOs, and possibly to
utilise the UKST Plate Library at ROE for "precovery" work, would enhance world-wide knowledge of
the threat and possible countermeasures.
38
The ideal location for such an establishment would be the Armagh Observatory. Armagh is an
acknowledged centre for minor planet studies and many of the personnel required already work there.
The necessary infrastructure is already in place.
Advantages
1.
The expertise, and much
infrastructure is already in place.
of
the
2.
The commitment of the UK to planetary
defence would be demonstrated to the world.
3.
Initial costs would be low, but running costs
would be a substantial proportion of those required
for Options 1 and 2.
Disadvantages
Figure 27 - Part of a typical photographic
plate
1.
The priorities laid down above would not
be fulfilled, and the centre would be dependent on
external observations (except for the data already available on the UKST plates). Much of this work is
already done by the MPC, so there is a risk of effort duplication.
Project Phases
q
Phase 1 - Groundwork
Year 0 - 0.2
Initial team selection
Feasibility study
Initial sponsorship trawl.
q
Phase 2 - Preparation
Year 0.2 – 0.5
Compilation of a business plan.
Operational personnel selection
Costing of necessary support resources (IT, Communications).
q
Phase 3 - Funding and Support
Year 0.5 – 0.7
Search for sponsorship.
Lobbying of national and international organisations for funding and support (Commercial interests,
IAU, NASA, UN, DTI, BNSC, PPARC, academia)
q
Phase 4 - Development
Year 0.7 - 1
Hardware and software development
Establishment of link with MPC
Personnel training
q
Phase 5 - Operations
Year 1 ->
Operations & upgrades
Costs
Project costs will depend on the size of team chosen, and the requirement for hardware and support.
It is unlikely that costs would exceed:
Set-up costs
Running costs
£ 60,000
£ 450,000 pa
39
Total cost of a ten-year project
£ 4,560,000
19-13. OPTION 4 - Establish an Amateur Network for Follow-Up Observation.
General
Amateurs around the world already do much of the follow-up observational work. However, the task
requires dedication, and a certain amount of fairly expensive equipment. It is unlikely that it would be
possible to establish an effective network in the UK for an extended period of time without fairly
substantial funding for equipment and a dedicated information node.
Advantages
1.
Low initial and running costs
2.
The participation of numbers of amateurs in a valuable observational programme will raise the
profile and appreciation of the subject.
Disadvantages
1.
The UK is far from ideal as a site for NEO detection or follow-up observations due to light
pollution, poor weather and seeing and the geographical location.
2.
The co-ordination of an extensive amateur network would be difficult, requiring additional
some full-time staff at the Minor Planet Centre (MPC) which currently does this.
3.
Amateur equipment has limited capabilities for NEO detection, but is suitable for follow-up
observations.
40
20.
Conclusion
_________________________________________________________________________________
The realisation that any sort of threat from collision with cosmic debris exists is a relatively recent
phenomenon. As mentioned above, it was only in the latter half of the twentieth century that it was
generally accepted that the craters on the moon were caused by impacts as opposed to being
volcanic in origin. While there is no doubt that there is a substantial long term threat this hazard is
qualitatively different from other natural disasters such as earthquakes, floods or volcanoes:
Rare.
Major impacts are rare, therefore easy to dismiss as irrelevant to the current generation.
Indeed, the whole subject suffers from a substantial "giggle factor".
Devastating.
The destruction wrought by a major impact will be orders of magnitude greater than
any that resulting from other natural phenomena.
Avoidable.
It is now technically possible to avoid or, at least mitigate the effects of impacts.
Figure 28 - An asteroid approaches Earth
It is now becoming clear that cosmic impacts have played an important role in the geological and
environmental development of the Earth, and may even have been the dominant factor in the
evolution of life. This realisation is driving a paradigm shift in scientific thinking analogous with that
prompted by the publication of Darwin's "On the Origin of Species by Means of Natural Selection".
At the present time the only answer to questions about what is being done to predict and react to the
threat of collision with a comet or asteroid is "not much". As Dr. David Morrison of the NASA Ames
Space Science Division has pointed out, there are more people working in a single McDonald's fast
food outlet than there are dedicated to the specific search for near Earth asteroids or short period
comets, and even this number is dropping as funding becomes scarcer. However, interest is growing
fast in scientific and military communities and amongst the general public as more information
becomes available. While the public is still largely unaware of the potential threat, that ignorance is
41
diminishing. The impact of Comet Shoemaker-Levy 9 on Jupiter in the summer of 1994 began to
increase public and political interest. The visit of Comet Hale-Bopp and the distribution of a number of
television documentaries and feature films dealing with impacts will further increase public awareness.
The question of global defence will surely be raised in public forum.
In September 1993, the Economist published an article, authored by Oliver Morton, entitled "The
Threat from Space" which concluded with the following passage:
"There is nothing wrong with being blasé, and there is no reason to live in daily terror of death from
the sky. But there is a great danger in having minds so narrow that they can see no further than half a
lifetime in each direction. The asteroidal message that matters most is that the past, and the future,
may be hugely different from the present."
Those responsible for the welfare of their people might do well to take heed.
_________________________________________________________________________________
Acknowledgements. The author would like to thank Sir Arthur C Clarke, Sir Bernard Lovell, P. Moore, Sir Crispin
Tickell, M E Bailey, M Baillie, S V M Clube, S. Clucas, M. Genge, M. Grady, S. Green, P. Grego, J. Gribbin, N J
Holloway, D. W. Hughes, I. Lyon, J A M McDonnell, M. Martin-Smith, R. Matthews, W M Napier, B J Peiser, P.
Roche, J E Salt, D I Steel, J. Wall, I P Williams, J Zarnecki, W. Alvarez, D. Asher, D. Balam, P. Brown, G.
Canavan, A. Carusi, T. Gehrels, E. F. Helin, D. Levy, A. Maury, S. Ostro, M. R. Rampino, H. Rickman, J. Schiff,
C.J. Shoemaker, E.M. Shoemaker, G. L. Verschuur, S. P. Worden, D. K. Yeomans, without whose help and
advice the preparation of this paper would not have been possible.
_________________________________________________________________________________
Prepared by:
J.R. Tate
Director
Spaceguard UK
Spaceguard UK Contact Address:
Spaceguard UK
Cygnus Lodge
High Street
Figheldean
Salisbury
Wiltshire SP4 8JT
Telephone:
01980 671380
Fax:
01980 671381
E-mail:
[email protected]
Web Site:
http://ds.dial.pipex.com/spaceguard/