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Lecture 12
Surface and Atmosphere
of the Inner Planets
January 7a, 2014
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Terrestrial Planets
We’ll examine each planet starting from the atmospheres and working
inward to the surfaces and then the inner geology.
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Mercury Venus Earth Mars
Distance (AU) 0.4 0.7 1 1.5
Spin Period 59 days243 days
(retrograde)24 hours 24.6 hours
Orbital Period 88 days 225 days 1 year 1.9 years
Radius (R) 0.4 0.95 1 0.5
Mass (M) 0.055 0.8 1 0.1
Eccentricity 0.21 0.007 0.017 0.093
Moons no no 1 2
Basic Information
Atmosphere of the Earth
• Clouds of water vapor
• Seasonal variations (23º tilt)
• Protects us from
– harmful radiation
– meteoroids falling from space
• Keeps surface of planet warm
– Greenhouse effect
Nitrogen(78%)
Oxygen (21%) +
trace compounds
184 to 330 K
(−123°F to 134°F)
1 atm
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Atmosphere of Mercury
• No true atmosphere
– Temperature too high
– thermal velocity exceeds
escape velocity
• Extreme temperature
variations – No insulating atmosphere
– One solar day on Mercury
= 176 Earth days!
• No tilt
None
100 K (night) to
700 K (day)
(−279°F to 800°F)
0 atm
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http://www.nasa.gov/mission_pages/messenger
/multimedia/messenger_gallery.html
Atmosphere of Venus
• Permanent cloud cover
keeps surface hidden.
• Tilt = 177º
(i.e. retrograde spin)
• Little daily or seasonal
temperature variation.
• High temperatures due to
Greenhouse effect
Mostly CO2;
clouds = sulfuric acid
750 K (890°F)
90 atm
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Greenhouse Effect
• Sunlight hits
surface of
planet warming
the ground.
• Planet radiates
heat in the form
of infrared
radiation
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Greenhouse Effect
• Greenhouse gases
(CO2, H2O) trap
infrared radiation,
keeping the planet
warm.
• Planet eventually
comes to
equilibrium and
temperature stops
increasing
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Greenhouse Effect
• Greenhouse effect elevates average
temperature of Earth by ~23C (~41 F).
• Too much CO2 or other greenhouse gas in
atmosphere could elevate temperature even
more, changing climate on the Earth
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Moons
of Mars
Deimos (MRO)
Size ~ 15 × 12 × 11 km
Phobos (MRO)
Size ~ 27 × 22 × 19 km • Phobos and Deimos
• Irregular shape
• Heavily cratered
• Rotate synchronously
(like Earth’s Moon)
Phobos
(Viking 1)
10/19/1978
Atmosphere
of Mars
http://antwrp.gsfc.nasa.gov/apod/ap030602.html
CO2
100 to 300 K
(−279°F to 80°F)
0.007 atm
• Thin water
vapor clouds
and fog but no
rain.
• Strong winds
cause dust
storms
• Tilt = 24º
gives seasonal
variation
similar to
Earth.
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Wind Features on Mars
Image area ~ 2.3 x 3.6 km
Sand dunes in
Hellas Region
Global Dust-storm
Sand Dunes in Endurance Crater (Opportunity)
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Why is Venus’ surface hotter than Mercury’s?
A. Carbon dioxide in Venus’ atmosphere traps heat
that radiates from its surface.
B. Sulfuric acid in Venus’ atmosphere produces
thermochemical energy.
C. Venus is closer to the Sun than Mercury.
D. Venus rotates more slowly, so it “bakes” more in
the Sun’s heat.
E. Clouds in Mercury’s atmosphere reflect sunlight
back into space, keeping its surface cool.
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Why is Venus’ surface hotter than Mercury’s?
A. Carbon dioxide in Venus’ atmosphere traps
heat that radiates from its surface.
B. Sulfuric acid in Venus’ atmosphere produces
thermochemical energy.
C. Venus is closer to the Sun than Mercury.
D. Venus rotates more slowly, so it “bakes” more in
the Sun’s heat.
E. Clouds in Mercury’s atmosphere reflect sunlight
back into space, keeping its surface cool.
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Origin of Earth’s Atmosphere
• Original atmosphere
was H and He leftover
from formation of SS.
– Too hot near the Sun
– H and He are very
light elements.
• vgas > vescape
– Gravity of Earth could
not hold them.
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– CO2 dissolved in
oceans or
became locked
up in rocks.
• Second atmosphere was possibly out-gassed
from volcanoes.
– water vapor, methane, carbon dioxide (CO2),
nitrogen (N) compounds.
– N2 freed by UV light
– Earth cooled, water vapor condensed into oceans.
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• Current atmosphere is mainly N2 and O2
– 3.8 – 3.5 billion years ago life became established,
releasing O2 into atmosphere via photosynthesis.
– Free oxygen does not build up until ~ 2 billion years
ago
– Ozone layer formed after free oxygen increases.
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Continuing Questions
• Was atmosphere created gradually or were
most gases released early when surface was
still molten?
• Could comet impacts have added some
carbon dioxide and water? How much?
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Why are Venus and Mars
Different from the Earth?
• Venus -- too close to Sun
– Too hot for water to condense.
– CO2 was not trapped in the oceans.
– Increased the greenhouse effect
“Runaway Greenhouse Effect”
• Mars -- too far from the Sun
– Initially warm after formation, water condensed.
– Water froze, trapping CO2
– Less greenhouse effect
Mercury Messenger http://www.nasa.gov/mission_pages/messenger/main/index.html
http://en.wikipedia.org/wiki/MESSENGER
• Launched August 2004
• Arrived 2011
• Found water and water
ice
• Obtained visual
evidence of past
volcanic activity
• Determined the
planetary core is
partially liquid
http://messenger.jhuapl.edu/the_mission/artistimpression/atmercury_br.html
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Messenger Fly-by August 2, 2005 http://en.wikipedia.org/wiki/File:Mdis_depart_anot.ogv
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Surface of Mercury
• Appears similar to Moon
• Heavily cratered due to
bombardment by debris in
space early in history.
• No weather or geologic
activity
Any crater that is
formed remains.
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Craters on Mercury
Mercury Moon
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Surface Features
• Heavily cratered areas (similar to lunar
highlands)
– Surface likely 3.8 byrs or older
• Inter-crater plains (similar to lunar maria)
– Likely formed in same manner as on Moon.
– More craters than on lunar maria, so they likely
formed earlier than lunar maria.
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Inter-crater Plains
Scarps
• Cliffs in crust of
planet which cut
across craters.
– Formed when
interior cooled and
core shrunk more
than the crust.
– Crust developed
“wrinkles.”
before after
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Mare Orientale (Moon)
Caloris Basin (Mercury)
Caloris Basin • Enormous crater - possibly due to large impact
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Caloris Basin “weird terrain”
Weird Terrain
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Which surface feature is unique to Mercury?
A. Maria
B. Impact craters
C. Mountains
D. Scarps
E. Plains.
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Which surface feature is unique to Mercury?
A. Maria
B. Impact craters
C. Mountains
D. Scarps
E. Plains.
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spin orb3 2P P
Synchronous Orbit of Mercury
• Pspin=59 days
• Porb=88 days
• Mercury’s orbit is eccentric
(0.21)
• Mercury is slightly elongated
• Tidal forces of Sun try to align
Mercury
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Surface of Venus
• Mapped by
Magellan (radar)
probe
• Some craters
• Many volcanoes
• No water
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Venus - Magellan
• Radar maps of Venus
– (Left image – bright = rougher terrain)
– (Right image – colored to resemble Earth globe)
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Venus – Magellan
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Craters
• Impacts occur
• Fewer craters
– thicker
atmosphere
– geologic
activity
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Venera
• Venera probes (Russian) landed on Venus.
– Hot and dry
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Slow Retrograde Spin of Venus
• What would cause Venus to spin so slowly, and in the
opposite direction (clockwise when viewed from
above north pole) from most of the other planets?
– A collision with some large object?
– Tidal forces from the Sun?
– Atmospheric friction?
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Surface of Mars
• Red colored -- iron oxide (rust) in surface rocks.
• Canali
– Dark lines observed by Sciaparelli (1877)
– Believed to be irrigation channels.
– Natural surface features.
• No liquid water (too cold)
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General Surface Features • Northern Hemisphere =
“lowlands”
– Few craters = younger surface
– Lower average elevation
– Evidence for geologic activity
• Southern Hemisphere = “highlands”
– Many craters = much older surface
– Age ~3-4 byrs
Google Mars Map
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Surface -- Pathfinder Mission
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Pathfinder
Martian Landscape near Gusev
Crater – Spirit Rover
http://photojournal.jpl.nasa.gov/jpeg/PIA06770.jpg
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Mars Landscape in Gusev Crater –
Spirit Rover
marsrovers.jpl.nasa.gov/gallery/press/spirit/20040106c.html
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Martian
Landscape in
Meridiani
Planum –
Opportunity
Rover
marsrovers.jpl.nasa.gov/gallery/press/opportunity/20040125a.html
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Curiosity Rover • Landed in Gale crater August 6, 2012
• Twice as long and 5 times heavier than Spirit and Opportunity
• Found more evidence for large amounts of surface water in the past
http://www.nasa.gov/mission_pages/msl/multimedia/gallery-indexEvents.html
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Water on Mars
• Dry riverbeds seen
• Channels are ~4 billion years old.
Mars was warmer earlier in its history.
– Thicker atmosphere.
– Cooled slowly
Spherules on Mars
appear to have
condensed out of water
Opportunity
Rover in
Meridian
Planum
http://antwrp.gsfc.nasa.gov/apod/ap040210.htm
http://antwrp.gsfc.nasa.gov/apod/ap040405.html
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Dry Riverbeds on Mars
Nirgal Vallis
http://barsoom.msss.com/http/ps/channels/channels.html
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Where is the Water Now?
• Polar caps.
– water polar caps -- permanent
– CO2 caps grow during winter and shrink during
summer.
• Frozen under surface as permafrost.
• Occasional melting
– Volcanic activity
– Meteor impacts
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Polar Caps
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Water Distribution on Mars – Mars
Odyssey
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Water Distribution on Mars – Mars
Odyssey
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Life on Mars?
• Martian meteorite
– Found at South Pole
– May have been blasted off of Mars by an impact.
– Much debate over validity of results.
– Possible contamination by Earth life.
– Need sample from Mars.
• Viking -- tested soil samples, no clear evidence
for current life.
• Mars Pathfinder -- no clear evidence for current
life.
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We now know that water exists on Mars. This
water is in the form of
A. liquid in rivers only.
B. atmospheric water vapor only.
C. ice in polar icecaps only.
D. permafrost, polar icecaps, and atmospheric
vapor
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We now know that water exists on Mars. This
water is in the form of
A. liquid in rivers only.
B. atmospheric water vapor only.
C. ice in polar icecaps only.
D. permafrost, polar icecaps, and
atmospheric vapor
