Today’s APOD

Next: Chapter 9 – Outer PlanetsQuiz 7 todayRooftop on Nov. 10, Kirkwood Nov.

12Homework due TODAY

The Sun Today

A100 - Comparing Terrestrial Planets

The Martian Interior

Differentiated like the Earth’s interior into a crust, mantle, and iron core

Having a mass between that of dead Mercury and lively Earth/Venus implies Mars should be intermediate in tectonic activity Numerous volcanic peaks and uplifted highlands exist Olympus Mons and other volcanoes do not show any

craters on their slopes indicating they may still occasionally erupt

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Mars Topography

North• smooth surface• few craters• lower elevation• ***younger***

South• rough surface• heavily cratered• higher elevation• ***older***

Why are the northern and southern hemispheres of Mars so different?

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Hypotheses

1. Did a major impact (or several large impacts) resurface the northern hemisphere?

NO - Not circular, no rim…

2. Did an ancient ocean in the northern hemisphere eroded away the surface, erasing the craters?

NO - No shoreline, slopes not consistent, features at boundary suggest compression

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Plate Tectonics on Mars?

Rising material from the interior creates a “rift” and forms new crust

New crust spreads and is “subducted” where convection in the mantle pulls it down

Compression features will form where new crust encounters old crust

Subduction provides fuel for volcanic activity (Tharsis volcanoes?)

Largest Mountain in the Solar System

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More evidence for plate tectonics? The crust of

mars is thinner in the northern hemisphere

When a rift expands quickly, new crust is smooth and thinPlate tectonics cools the

interior; when the interior cools off, mantle convection ends, and plate tectonics stop.

S N

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Magnetic Stripes

• Mars once had a reversing magnetic field – a core dynamo like Earth’s

• Evidence of mantle convection and plate tectonics• Dynamo ended about 4 billion years ago, before the

interior cooled

• Surface magnetic field measured by MGS

• Bands of opposite N/S polarity

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Mars Topography

• A mixture of old and “really old” terrain

• Evidence suggests that plate tectonics resurfaced the northern hemisphere early in martian history

Linear shape of Valles Marineris suggests it was a rift formed through plate tectonics

The Atmosphere of Mars Clouds and wind blown

dust are visible evidence that Mars has an atmosphere

Spectra show the atmosphere is mainly CO2 (95%) with traces of N2 (3%), oxygen and water

The atmosphere’s density is about 1% that of the Earth’s

Not a drop of rain…

No rain falls, despite cloudsAtmosphere is too

cold and dryFog seen in valleys

and ground frost has been observed

CO2 “snow” falls on poles during winter

Ancient Atmosphere of Mars

Dry river beds indicate liquid water flowed in Mars’s past

This implies that Mars had to have a denser atmosphere (higher pressure) to prevent the fast vaporization of surface water into the atmosphere

Cratering indicates that this thicker atmosphere disappeared about 3 billion years ago

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Climate Change on Mars?

ModernCold and Arid

Past?Wet and Warm?

Percival Lowell first popularized the idea that early Mars was warm and wet

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Evidence for Water Ice on Mars

Polar caps

Surface frost, Viking 2

Ground ice (Mars Odyssey)

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Headscarp of Chasma Boreale1000 m of layered ice, frozen sand dunes, andlayered sedimentary rock above a cratered basement

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Viking orbiter found channels

Martian delta Fossil delta on Earth

Evidence for Flowing Water in the Past

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Two Causes of

Climate Change• Orbital and axial variations

• Long-term evolution

Mars is closer to the sun during its southern summer and further from the sun during the northern summer. The southern summer is shorter and hotter, while the northern summer is longer and cooler. The difference affects polar ice loss, weather patterns, and dust storms.

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• Large CO2 abundance up to ~ 3.8 Gyr allows warm climate and channels

• ~ 3.8 Gyr: Heavy bombardment removes much of early atmosphere

• Further loss of CO2 to carbonate minerals and escape gradually reduces CO2 to present levels

The Martian Atmosphere – Standard Model

But – some problems with this model (nitrogen abundance doesn’t match, not enough carbonates on Martian surface)

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Alternate Models

• Transient warmings?– large impacts– thermal events, volcanoes

• Water features caused by other fluids?•Pyroclastic flows•Sulfur-rich fluid lavas

W. K. Hartmann

Comparing the

Terrestrial Planets

?

Role of Mass and Radius Mass and radius affect interior temperature This in turn determines the level of tectonic activity Low-mass, small-radius planets will be cooler inside

and hence less active than larger planets This relationship is in fact observed with Mercury

(the least active), then Mars, then Venus/Earth

The Role of Sunlight

Warming from sunlight depends on the planet’s distance from the Sun – the closer the warmer

Warming also depends on the amount and makeup of the atmosphere

Solar warming and atmospheric chemistry also determines the structure of the atmosphere, which may affect the amount of warming On warmer Venus lifts water vapor to great heights in its

atmosphere On cooler Earth, water condenses out at lower heights and

the upper atmosphere is almost totally devoid of water

The Role of Biological ProcessesBiological processes remove CO2 from the

atmosphereSea creatures use dissolved CO2 in ocean

water to make shells of calcium carbonateShells fall form sediment on the ocean bottom Sediment becomes rock, sequesting CO2

With CO2 removed, mostly N2 is leftCO2 is recycled back into the atmosphere by

tectonic activityGreen plants break down H2O, C02 during

photosynthesis, producing oxygen

Comparing Planets Mercury

Low mass No atmosphere No plate tectonics Old crust No life

Venus Massive Extensive

atmosphereActive vulcanism?New crustNo plate tectonicsNo Life

Earth Massive Modest

atmosphere Some vulcanism Plate tectonics New crust Life

Mars Medium Mass Thin CO2 atmosphere

Some vulcanism Early plate tectonics? Old and not-so-old crust Life?

ASSIGNMENTSthis week

Next Week – Ch 9 – Outer Planets

Rooftop session on Nov. 10 Kirkwood Open Nov. 12 Turn in homework!