Structure of Mercury

1
Structure of Mercury
(from Mariner 10 and theoretical arguments)
1.Crust 100-200 km thick 2. Mantle 600 km
thick 3. Core, 1800 km in radius
And no atmosphere, so no wind or erosion.
Surface reflects geologic history well.
2
Venus
Mass 0.82 MEarth Radius 0.95 REarth
? Density 5.2 g/cm3 Average distance from
Sun 0.72 AU Orbital period 225
days Rotation period 243 days (longer than
orbital period, and retrograde!)
3
Venus' Atmosphere
- Pressure at surface is 90 x that of Earth's gt
much more gas in atmosphere. No oceans. -
Consequence - meteoroids burn up easily. No
impact craters less than 3 km. Whats the
composition of the atmosphere?
- 96.5 CO2 - Yellowish color from sulfuric
acid clouds and haze.
- Hot at surface - 730 K! Almost hot enough to
melt rock - Why so hot? Huge amount of CO2
leads to strong greenhouse effect.
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Early on, T may have been much lower (but still
warmer than Earth). Oceans existed? But if warm
enough, T would start to rise because of...
Runaway Greenhouse Effect 1) Water and CO2
evaporate from oceans into atmosphere. 2)
Greenhouse effect more efficient. 3) Temperature
rises. 4) More evaporation (back to 1).
gt complete evaporation of oceans. Thick
atmosphere.
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The Habitable Zone or The Goldilocks Problem
In the zone
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Missions to Venus
Soviet Venera 4 -18 (1967 - 1983) Mariner 2, 5
and 10 (1962, 1967 and 1974) Pioneer Venus
(1978) Magellan (1989)
Venera 13 photo of surface. Rocks are basalt and
granite. Color is due to atmosphere.
Color corrected for atmosphere.
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"Radar Echo" technique measures altitude
space probe
time for signal to return tells you the altitude
of surface feature.
Planet Surface
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Radar data (Pioneer Venus mission) reveal
altitude variations on surface. Flatter than
Earth, no evidence for plate boundaries gt no
large scale plate tectonics.
But plenty of evidence of stresses and fractures
on smaller scales gt much small-scale shifting of
crust
1 km
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Impact Craters
Unlike Moon, larger impact craters distributed
randomly over surface gt all parts of surface
have about same age.
Paucity of large impact craters gt surface is
young, 200-500 million years?
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Volcanism
Shield volcano elevation map from Magellan radar
data. About 100 km across. Volcanism may be
ongoing, based on sulfur dioxide variations in
atmosphere. But very little resurfacing in past
200-500 million years.
Venus surface flyover
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Volcanism
Venus surface flight simulation using data from
Magellan.
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Clicker Question
Why is Venus the hottest planet in the Solar
System? A It is the closest planet to the
Sun. B There is a lot of radioactive material
in the crust. C There is a large concentration
of carbon dioxide in the atmosphere. D The
Russians left the lights on in the Venera 5
landing vehicle. E. Paris Hilton lives there.
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Mars
eccentricity 0.093 Range in distance from Sun
1.38 - 1.66 AU Rotation Period 24.6
hours Orbital Period 687 days
Mass 0.11 MEarth Radius 0.53 REarth
Density 3.9 g/cm3 Average distance from
Sun 1.52 AU
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The Martian Atmosphere
- 95 CO2 - Surface Pressure 0.006 that of
Earth's atmosphere (thin air!) - Surface
Temperature 250 K. - Dust storms sometimes
envelop most of Mars, can last months.
A Reverse Runaway Greenhouse Effect? During
volcanic phase (first two billion years), thicker
atmosphere, warmer surface, possibly oceans.
Gradually most CO2 dissolved into surface water
and combined with rocks, then atmospheric and
surface water froze (creating ice caps and
probable permafrost layer).
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Mars' Moons Phobos and Deimos
Phobos 28 x 20 km
Deimos 16 x 10 km
Properties similar to asteroids. They are
probably asteroids captured into orbit by Mars'
gravity.
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Clicker Question
From Mars, Deimos has an angular diameter of 140
arcseconds. Would colonists on Mars ever see
Deimos produce a total solar eclipse? A Yes,
every day on Mars B Yes, every new moon C
Yes, but rarely D Never
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The Martian Surface
Olympus Mons
Tharsis Bulge
Valles Marineris
Southern Hemisphere 5 km higher elevation than
Northern, and more heavily cratered. South is
like lunar highlands, surface 4 billion years
old, North like maria, 3 billion years
old. Valles Marineris - 4000 km long, up to 7 km
deep. Ancient crack in crust. Reasons not clear.
(Mars Global Surveyor radar data)
Tharsis Bulge - highest (10 km) and youngest (2-3
billion years) region. Olympus Mons - shield
volcano, highest in Solar System, 3x Everest in
height. 100 km across.
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View From the Surface
Dry, desert-like. Red gt high iron content.
Mars didn't differentiate as completely as Earth.
Sky has butterscotch hue due to dust.
Viking 1 site (1976)
Sojourner robot from Pathfinder (1997)
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Opportunity panorama inside Victoria Crater
Deepest crater explored by far (230 feet) gt
apparently it was the top of an underground water
table.
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Evidence for Past Surface Water
"runoff channels" or dry rivers
"outflow channels"
South
North
teardrop "islands" in outflow channels
standing water erosion in craters?
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Pathfinder site was an outflow channel
Red arrows rounded boulders indicating water
erosion? White arrows "conglomerate" rock, like
in Earth's riverbeds? Blue arrows sharp-edged
boulders, volcanic rock?
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Did Mars once have a huge ocean?
Long stretches along border are very even in
elevation, like a coastline
Ocean fed by outflow channels from higher
elevation southern hemisphere?
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Evidence for "Permafrost" layer beneath surface
"Splosh" craters suggesting liquefied ejecta.
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Evidence for Water on Mars Now
subsurface ice
Phoenix Lander (2008) Deployable arm
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Phoenix mission icy soil at the poles!
Phoenix analyzing scooped up dirt was Mars ever
favorable for microbial life? Organic compounds?
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Mars' History
Smaller than Earth, Mars cooled
faster. Atmosphere and surface water in first
1.5 billion years. Life? Most volcanic activity
ended two billion years ago. Differentiation
less complete than on Earth. No evidence for
plate tectonics. Atmosphere mostly froze out
into subsurface ice, polar ice caps and surface
rocks.
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Clicker Question
The largest mountain in our solar system is A
Caloris Basin range on Mercury B Gula Mons on
Venus C Mt. Everest on Earth D Olympus Mons on
Mars
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Clicker Question
Where is the water that once flowed on the
surface of Mars? A In the atmosphere B In the
polar caps only C In a layer of permafrost
below the surface and in the polar caps D It
was diverted to Los Angeles
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• Martian Snick meteorite ALH84001 shows odd
  shaped features that are reminiscent of bacteria.
  General consensus is no life.

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Valles Marinaris flyover movie
31

• The Face on Mars
• Viking orbiter photos showed this

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• Newer, high resolution photo Mars Global
  Surveyor 1998

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• Isnt this more disturbing???

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Spirit and Opportunity Rovers Scenes from
Roving Mars (start at 1510, skip to 2027,
skip to 2616)