REVIEWS
Planetary science
for all
Does the Sun
make us hot?
Encyclopedia of Planetary
Sciences
eds James H Shirley and Rhodes
W Fairbridge
Chapman and Hall, London,
990 pp and 32 colour plates,
ISBN 0 412 06951 2.
The Manic Sun
by Nigel Calder
1997, Pilkington Press, London,
211 pp, £24.95, ISBN 1 899044
11 6.
It is roughly 30 years since the systematic exploration of first the
Moon and then the other planets
and satellites of our Solar System
began. During that period, every
major object in the Solar System
with the exception of Pluto has
been examined in reasonable detail
by at least one spacecraft mission.
And during the last decade a start
has been made on the examination
of the primitive asteroids and
comets, whose chemical and physical nature hold the clues to the origins of all of the larger bodies.
The techniques used to obtain the
basic data have been drawn from a
wide range of traditional scientific
disciplines, including astronomy,
geology, physics, chemistry, geophysics and biology. Furthermore,
some newer fields, such as remote
sensing and image processing, have
emerged largely as a result of the
impetus of planetary exploration by
orbiting satellites. All of these disciplines can be referred to collectively
as the planetary sciences. However,
the process of synthesizing the very
large body of knowledge about the
planets which has progressively
accumulated has led to the recognition by many workers in the field
that planetary science (in the singular) should be regarded as a subject
in its own right.
This is very much the philosophy
adopted by the editors of the Encyclopedia of Planetary Sciences,
despite the fact that they have
retained the plural “Sciences” in the
title. Drawing on inputs from all of
the traditionally separate disciplines
mentioned above, they have succeeded admirably in driving home
the point that the Earth is just one
member of a group of planets and
satellites which are subject to
numerous common processes.
Of course, no one process is
important on all of the bodies, a
point driven home when one
recalls the major subdivision of
objects in the Solar System into the
atmosphere-dominated gas giant
planets and essentially everything
else. However, the common themes
February 1998 Vol 39
which emerge involve geological,
geophysical, hydrological, atmospheric, ionospheric, and impact
cratering processes. Those who,
like myself, support the idea that
planetary science is a single discipline would argue that the study of
these processes operating under
different boundary conditions
helps us obtain a better understanding of the processes themselves, as well as of the bodies on
which they operate.
The range of topics dealt with in
the Encyclopedia is very large
(there are more than 460 articles,
arranged alphabetically), and
includes not only the themes mentioned above, usually dealt with
separately as they apply to each of
the planets and the Sun, but also all
of the basic astronomical (Earthand satellite-based) and celestial
mechanics techniques needed to
obtain data on the rest of the Solar
System, together with 22 separate
entries for individual spacecraft
missions and brief biographies of
65 scientists prominent in the history of planetary investigation.
The work is pitched at a wide
audience, from experts to interested
laypersons, and each entry contains
a short bibliography and a list of
cross-references to related entries.
To help those who are unfamiliar
with the field, an appendix groups
all the entries into 15 major themes.
The subject index is comprehensive,
and there is an author index for the
bibliography references.
No encyclopedia involving the coordination of so much information
(from 214 contributors) can expect
to be entirely up to date when it is
published. In this case, production
appears to have taken about two
years, given that the topics covered
and the literature references seem to
be complete as of some time in
1995. It is inevitable, therefore, that
there is no reference (other than in
anticipation) to the exciting new
data on Jupiter and its satellites
currently flowing from the Galileo
spacecraft.
However, apart from this, the
synthesis of results from all of the
earlier planetary missions is generally excellent, and my random sampling of entries relevant to the fields
in which I work revealed nothing
with which I felt inclined to disagree strongly. In short, this volume
should prove an extremely valuable
source of information for a very
wide audience.
Lionel Wilson.
The global climate has varied greatly over past ages, by far more than
the recent global warming of around
half a degree this century, currently
of such concern among environmentalists. The simplistic popular view,
as represented in the media, is that
the recent warming is due entirely to
the “greenhouse effect” caused by
emissions of carbon dioxide from
the burning of fossil fuels. Scientific
opinions are more varied, but the
overwhelming consensus at present
is that anthropogenic activities are
having a discernible effect on our
climate, though extrapolating to
predict future trends is fraught with
uncertainty. Calder is a heretic to
this orthodoxy. In The Manic Sun
he argues, and quite persuasively,
that with the exception of certain
“internal” phenomena such as El
Niño, and volcanic eruptions like
Pinatubo, all climate variability
including the recent warming is
entirely due to the external influence
of the Sun.
In astronomical terms the Sun is a
pretty ordinary star, but it is our
Sun and human life depends upon
it. Its surface is a highly complex
and dynamic region of turbulent
hot magnetized plasma, which has
recently come under intense probing by the Yohkoh and SOHO solar
observing satellites. The Earth is
embedded in the solar atmosphere
(the heliosphere) and is constantly
buffeted by the solar wind, which
expands outwards from the solar
corona. Frequent coronal mass ejections of hot plasma, though partially deflected by the Earth’s magnetic
shield (the magnetosphere), cause
massive disturbances in the upper
atmosphere: the aurora, major magnetic storms, enhancement of the
radiation belts. Such effects can
cripple communications satellites,
and disrupt power transmission and
navigational systems. The link with
the lower atmosphere and climate
is, however, rather more tenuous.
Although many of the solar–
terrestrial effects mentioned above
have been explored only in recent
years, the Sun’s variability as manifested by sunspot activity, with its
roughly 11-year oscillation, has
been recognized for much longer.
1.31
REVIEWS
The point of the
turning world
YOHKOH/ISAS
Historical Eclipses and Earth’s
Rotation
by F Richard Stephenson
1997, Cambridge University
Press, hb, ISBN 0521461944,
557 pp, £90.
That the climate is influenced by
solar variability is suggested by the
coincidence between the almost
complete absence of sunspots during
1645–1715 (the Maunder minimum) and the coldest phase of the
Little Ice Age in Europe, when Frost
Fairs were held regularly on the ice
of the Thames. Calder describes this
relationship as well as more recently
discovered ones such as the close
correspondence between mean land
temperatures and the length of the
solar cycle. The latter was published
in 1991 by Friis-Christensen and
Lassen, two scientists working at
the Danish Meteorological Institute
in Copenhagen. Research for the
book was done during visits to this
institute, and it figures prominently
in the narrative.
The final conclusion, which is proclaimed as “the missing link”
between solar variability and climate change, is that recent climate
variations are caused by the effect
of cosmic rays on cloud cover. In
passing, doubts are aired about how
well the effect of clouds is taken
into account in large-scale climate
models. Calder’s proposed scenario
is that as the Sun becomes more
active, it shields the Earth more
effectively against cosmic rays
(called the Forbush decrease). Since
cosmic rays contribute to cloud formation by forming condensation
centres (as in a cloud chamber), an
increasingly active Sun leads to
reduced cloud cover and thus less
incoming radiation is reflected from
the atmosphere, with resultant
warming. The evidence is an impressive correlation between cosmic rays
and cloud cover, again published by
1.32
the Copenhagen group.
This is a popular book, not an
academic one. It is written for the
non-specialist in a clear non-technical style. There are good quality
pictures, many in colour, on nearly
every page. The author gives a very
readable description of solar and
solar–terrestrial processes, solar–
terrestrial interactions, and the supposed connection to climate.
The positions of the greenhousewarming advocates and the sceptics
are described in some detail, and
the background to and evolution of
the greenhouse-warming debate
over the past decade are well treated. The book is packed with useful
facts and information, and should
be of interest to a wide audience. It
is well up-to-date, with images
from SOHO, and of the tragic failure in June 1991 of the launch of
Cluster: four identical satellites
designed to answer many of the
outstanding problems in solar–
terrestrial physics. But this book is
not just an account of the science.
Calder tells the story behind the science: the political manoeuvrings as
the international efforts to try to
limit climate change by controlling
carbon dioxide emissions gathered
momentum; and the concerns of the
working scientist, with grants, referees, rivalries etc, all help to hold
the reader’s interest.
This book probably won’t cause
many people to change their minds
about greenhouse warming, but it
should convince them that the
effect of solar variability on the
Earth’s climate needs to be taken
seriously.
Andy Smith.
One of the early lessons that most
children learn is that, when walking
along a pavement, you have to
avoid stepping on the cracks otherwise the bears will get you. Either
Richard Stephenson’s parents were
remiss, or he was a poor learner,
since he has spent much of his
career treading firmly on the cracks
between astronomy, geophysics, history and philology. This book
shows how valuable such reprehensible behaviour can sometimes be.
Once the orbital elements of the
Earth and Moon are accurately
known, they can be used to predict
the details of both solar and lunar
eclipses – time, path of totality,
degree of obscuration etc. But the
observations do not quite fit with
the predictions, particularly for
ancient eclipses. This is because the
Earth is not a perfect timekeeper
and so the uniform days used for
the prediction differ slightly from
the days measured by the rotation
of the Earth. By studying the misfits
between prediction and observation, the variations in the rate of
rotation of the Earth since 700 BC
can be deduced.
Simple? Well, no! It is a Herculean task involving the collection
of reports of historical eclipses,
which tend to be incomplete (lumps
of clay tablet missing, or the
reporter failing to note vital details
such as the time and location) in
exotic languages (Babylonian,
Assyrian, Chinese etc) and with ref-
erence to obscure calendars. Each
report presents a problem which
can be solved only by scholarship
of the highest order to yield useful
scientific data. But do not be put
off. Stephenson leads his readers
gently and authoritatively through
the whole fascinating process and
emerges with a solid and invaluable
contribution to geophysics.
For anyone interested in any of
these topics, or simply as a collection of excellent detective stories
that do not involve a single corpse,
this book is thoroughly to be
recommended.
Stuart Malin.
Web wanderings:
A good fight
It is always fun to watch a good
academic scrap, and the Web can
provide an excellent vantage point.
Take the issue of the small comets
that may rain down on our atmosphere, at a rate of roughly 20 a
minute. Their existence was suggested in the mid-1980s by Louis
Frank and John Sigwurth of the
University of Iowa. They reiterated
their claim earlier this year, complete with photos.
The Fall Meeting of the American
Geophysical Union in December
proved a timely place for debate.
Frank and Sigwurth had further evidence in support of their ideas: they
had found that the number and size
of dark spots in the UV picture of
the atmosphere – evidence for
absorption of radiation by water –
decrease when viewed from a much
higher elevation. The full story and
pictures can be found at http://
smallcomets.physics.uiowa.edu/.
Debate there was in plenty: James
Spann and others from NASA’s
Marshall Space Center claimed that
the dark spots on the UV images
were instrumental artefacts, pointing out that the Ultraviolet Imager
had produced dark pixels during
tests on the ground with the sensors
fully illuminated. A summary at
http://science.msfc.nasa.gov/
newhome/headlines/ast09dec97_1.
htm gives this side of the argument
and links to other views.
The disadvantage of following a
debate such as this on the Web is
the lack of editorial or peer review
control; advantages include fast and
easy access, the chance to evaluate
claim and counter-claim at your
leisure, and, from the press releases,
some great quotations.
Sue Bowler.
February 1998 Vol 39