Admin. 9/20/16
1. Class website http://www.astro.ufl.edu/~jt/teaching/ast1002/
2. Optional Discussion sections: Tue. ~11.30am (period 5), Bryant 3; Thur.
~12.35pm (end of period 5 and period 6), start in Pugh 170, then
Bryant 3
3. Office hr: Tuesday 12.30-1pm; Wed. 12.30-1.00pm, Bryant 302 (but
email me if coming on Wed.).
4. Homework 4: is due Thur. Sept 22nd 11.59pm via Canvas e-learning
under “Quizzes”
5. Reading this week: Chapters 0, 1, 2.1-2.4, 4.1, 5, 6
6. Midterm 1: Tue. Sept. 27th, in class BRING YOUR UF ID TO THE
EXAM. For review go to Discussion Sections or Office Hrs. Best
preparation is to review class notes (up to Lecture 14) and homework &
quizzes, then also the textbook. You will not be able to use a calculator
or refer to your class notes in the exam. You will receive a list of formulae
(see next slide). Exam is multiple choice, similar to HWs. Bring a pencil.
7. Observing project deadline: Thursday Oct. 27th 2016, however, you
are strongly advised to complete observing by Fri. Oct. 7th.
8. Email me Astro-news, jokes, tunes, images: [email protected]
9. Printed class notes? Name tags?
Formulae (will be displayed for you in Midterm 1):
Speed = distance / time
Key Concepts: Lecture 13
Terrestrial Planets: Overview - How do the properties of
planets depend on their mass?
Mercury
Mars
The Planets
Angular size: θ = size / distance
Kepler’s 3rd Law: P2 = a3
[ Newton’s version of Kepler’s 3rd: P2 ∝ a3/(m1+m2) ]
Newton’s 2nd Law: F = m a
Newton’s Law of Gravity: F ∝ m1 m2 / r2
Density = mass / volume
Volume of a sphere = (4/3)πr3
Surface area of sphere = 4πr2
Frequency: f = 1/Period
Speed of wave (light) = frequency x wavelength: c = f λ
The Terrestrial Planets
Orbit and Rotation
Mercury - Overview
• Closest planet to the Sun:
a=0.4AU
• Only a little bigger than the
Moon
Property
Radius
Mass
Density
Escape Speed
Atmosphere
Magnetic Field
Mercury
2430 km
3.3 x 10 23 Kg
5430 kg/m 3
4.3 km/sec
(Very thin!!)
Sodium,
Potassium
3.0 x 10 - 7 T
Earth
6378 km
6.0 x 10 24 kg
5520kg/m3
11.2 km/sec
Nitrogen,
Oxygen
4.0 x 10 -5 T
Basically no atmosphere
Exploration of Mercury
• Telescopic Observations
–Very difficult to observe since it
is always near the Sun
–Giocanni Schiaparelli made a
map of subtle dark and bright
areas (1877)
• Space craft exploration
–Mariner 10 (1973-1974)
–Messenger (2008+)
• Orbital Period = 88 days
– Most eccentric orbit of any planet
• 46 million km to 70 million km
• Sunlight varies by factor of 2.3
[INVERSE SQUARE LAW FOR FLUX
Flux from Sun = Luminosity/(4πr2) ,
where r is distance from Sun; we will discuss later in
class]
– Was found to precess more than Newton’s Laws would
predict
• Planet Vulcan? Never found
• Einstein's Theory of Relativity is the explanation (more
later in the class)
• Rotation = 59 days
– Rotates 3 times in 2 orbits
– This synchronization is due to tidal effects from Sun
Structure of Mercury
• No seismic data
• Small planet - interior
will be relatively cool
and solid
• Large metal core
– Density roughly equal to Earth
– Mercury has less gravity so
material will be compressed less
– Thus metallic core should be
relatively larger than Earth’s
• Thin solid mantle
Surface of Mercury
• Similar to Moon
• Lots of impact craters
– Surface is very old
– No plate tectonics
– Craters flatter & have thinner ejecta rims
than lunar craters - due to higher gravity on
Mercury than on the Moon
• Some large filled basins similar to lunar
Maria (but not as extensive)
– Less cratered and younger
– Probably filled with lava from mantle after large impact
• Scarps - Cracks and cliffs in the crust; Young
- few craters cut them; Probably due to
Mercury shrinking as its core cooled not due
to plate tectonics
Mars
Scarp
Water on Mercury?
• Polar craters never have
sunlight in them
• Radar maps from the Earth
see:
–Pole is a bright region of
planet
–Could be frozen water
Mars - Overview
North
Pole
Mercury’s Atmosphere
• Very, Very thin!!! Basically no atmosphere, because very hot surface with low
escape velocity. Large temperature changes: Day = 700K; Night = 90K
• Small amounts of some elements are trapped from solar wind
• Sodium and Potassium (gas phase metals) most abundant in the atmosphere
– From surface impacts or solar wind
• Smaller than Earth
• Two very small moons
Property
Radius
Mass
Density
Escape Speed
Atmosphere
Mars
3397 km
6.4 x 1023 kg
3040 kg/m3
5.0km/sec
Carbon dioxide,
Nitrogen
Earth
6378 km
6.0 x 1024 kg
5520kg/m3
11.2 km/sec
Nitrogen,
Oxygen
Early Earth-Based Telescopic
Exploration of Mars
• Giovanni Schiaparelli - 1877
• mapped bright and dark regions
• saw polar caps which changed with
seasons
• Surface colors appeared to change Plant life?
• identified long narrow features
(channels - canale)
• Percival Lowell (1855-1916)
• Built observatory in Flagstaff to study
Mars
• Thought the “canals” were used by a
civilization to bring water to a desert
planet
Spirit & Opportunity
• Spirit travelled ~5 miles;
Opportunity ~15miles
• Evidence liquid water was
once on Mars
Space Craft Exploration of Mars
[You do not need to remember all the details of these missions]
• 1965 Mariner 4, 6 & 7 “flew by” Mars
– Craters
• 1971 Mariner 9 orbited and mapped
Mars in detail
– Valleys and volcanoes
• July 20, 1976 Viking 1 landed on
Mars
– Searched for life
• Mars Pathfinder (1997) placed a small
rover on Mars to study the chemistry of
its rocks
• Mars Rovers, Spirit and Opportunity
(2004)
• Mars Phoenix lander (2008)
• Curiosity (2012)
Curiosity
Structure of Mars
• Relatively low density
compared to earth
• No evidence of plate
tectonics (e.g., no
horizontal motion of
the crust)
• Impact craters
–Small dense core
–Thick mantle
• Mars global surveyor
found a very weak
magnetic field (1997)
–Surface is old and
heavily cratered
–Some are eroded
–Liquid/rotating core
The Surface of Mars
• It really is red
– Due to iron oxide
(Rust!)
• Lots of loose rocks
and sand
The Surface of Mars
– Loose sand from wind
erosion
• blows and drifts around
rocks
– Loose rocks from
• impacts
• flooding etc.
Volcanoes on Mars
• Volcanism is not as wide spread on Mars
as on Earth
• A few large Volcanoes
– Olympus Mons
• 24 km high (78000ft)
• 500 km in diameter
– All located on Tharsis bulge
• Why so big?
– lower gravity
– hot spot stayed in one place - no
continental drift
– thicker mantle to hold it up
The Surface of Mars - Valleys
• Valles Marineris
Liquid water on Mars today?
• Possible recent flows of water
–4000 km long
–2-7 km deep
• Large crack
–Due to stretching and
cracking when Tharsis
bulge formed
–Not due to water flow
Surface of Mars Flood Plains and River Systems
• Many flood plains and river
systems
–Liquid water certainly flowed
over much of Mars
• Many are old (~4 billion
years) i.e. cratered.
Wind Features
• Sand dunes and erosion
features
–Wind erosion features are due to
loose dust blowing around objects
• These are very wide spread
• Seasonal dust storms occur
with very high winds when
Mars is warmest
The “Face” on Mars
• One Viking orbiter image revealed a
mountain that looked somewhat like a
monkey face
–Commented on in a NASA press
release
–Immediately seized by tabloids
–Taken by some as proof that an
advanced civilization existed on
Mars
–Example of how our minds find
familiar patterns
Ice Caps on Mars
• Northern ice cap is much larger than
southern ice cap
– We’re not sure why.
• Composed of C02 ice & some water ice
• Size varies with season
– Seasons on Mars are due to its axial
tilt and somewhat elliptical orbit
– tilt of orbital axis is primary cause
– CO2 in northern hemisphere
completely sublimes in summer
leaving mostly water
The Atmosphere of Mars
• Low density: only 1% of Earth’s
atmosphere
Resolution: each
pixel = 43m
– CO2 (95%), Nitrogen(3%), O2 (.15%)
– Due to lack of large scale volcanism to return CO2 to
atmosphere
• Weak greenhouse effect
– Temperature range: 150K to 295 K
– Only about +5C warmer than without
• Large dust storms
– When Mariner 9 arrived surface completely covered by
dust
– Explanation of color changes rather than plants
– Seasonal: occur when Mars is heated most by the Sun
The Moons of Mars
Deimos
• Mars has two very small moons
– Phobos and Deimos
– 27 and 15 km across
• Do not look like our Moon
– Too small for their gravity to make them round
– Cratered and very irregular
• Origin
– May be fragments from a moon-asteroid
collision
Phobos
Open Questions About Mars
• Are there still active volcanoes?
• Where has the water gone?
–How much sub-martian water is there?
• Could there be life hiding some place on
Mars?
Life on Mars?
• Viking landers performed experiments to test
for presence of microbial life - inconclusive.
• Claims of microbial structures in a Martian
meteorite: inconclusive.
Humans to Mars?
Discussed in class