Inner Planet Surface and Atmospheres · Atmosphere of the Earth • Clouds of water vapor •...

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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 (NASA Messenger 2008) 28

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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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Martian Gullies 51

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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