EART 160: Planetary Science

NASA/JPL/Malin Space Science Systems

• Planetary Surfaces– Tectonics– Stress and Strain– Faults and Folds

Last Time

Homework

• Keep your units! Make sure things come out dimensionally.

• Watch those negative signs! Potential Energy is NEGATIVE.

RGME

RRGME

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UUE

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RGME

RGME

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Wrong Way Right Way

Not EquivalentExpressions

Emits negative energy?

Factor of 2 here

Today

• Paper Discussion– Mars Crust and Mantle (Zuber et al., 2001)– Io Volcanism (Spencer et al., 2007)

• Planetary Surfaces: Gradation– Fluvial (Water)– Aeolian (Wind)– Glacial (Ice)– Mass Wasting (Gravity)– Sputtering (Charged Particles)

• Planetary Surfaces: Tectonics– Elastic Flexure

Gradation

• Erosion, Transport, and Deposition of surface materials.– Rapid compared to other geologic processes

• Erosion – Displacement of solid material by ice, wind, or water– Weathering – chemical breakdown of minerals in the

rocks, often concurrent w/ erosion, but distinct• Mass Wasting – Downslope movement of

material due to gravity• Sputtering – Alteration of the surface due to

charged particles (solar wind)

Erosion and Deposition• Require the presence of a fluid (gas or

liquid) to pick up, transport and deposit surface material

• Liquid transport more efficient• Important process on Earth, Mars, Titan,

Venus• Aeolian: Wind• Fluvial: Flowing Water• Lacustrine: Lakes• Glacial: Ice

Aeolian Features (Mars)• Wind is an important process on Mars at the present

day (e.g. Viking seismometers . . .)• Dust re-deposited over a very wide area (so the

surface of Mars appears to have a very homogenous composition)

• Occasionally get global dust-storms (hazardous for spacecraft)

• Rates of deposition/erosion almost unknown

30km

Martian dune features

Dust Devils

Image of a dust devil caught in the act

Aeolian features (elsewhere)Namib desert, Earthfew km spacing

Yardangs (elongated dunes)Mead crater, Venus

Longitudinal dunes, Earth (top),Titan (bottom), ~ 1 km spacing

Wind directionsVenus

Wind streaks, Venus

Global patterns of wind direction can be compared with general circulation models (GCM’s)

Mars (crater diameter 90m)

Fluvial features• Valley networks on Mars• Only occur on ancient

terrain (~4 Gyr old)• What does this imply

about ancient Martian atmosphere?

30 km

• Valley network on Titan• Presumably formed by

methane runoff• What does this imply

about Titan climate and surface?

100 km

• Large-scale fluvial features, indicating massive (liquid) flows, comparable to ocean currents on Earth

• Morphology similar to giant post-glacial floods on Earth

• Spread throughout Martian history, but concentrated in the first 1-2 Gyr of Martian history

• Source of water unknown – possibly ice melted by volcanic eruptions (jokulhaups)?

Martian Outflow channels

50km

flowdirection

150km

Baker (2001)

Martian Gullies• A very unexpected discovery

(Malin & Edgett, Science 283, 2330-2335, 2000)

• Found predominantly at high latitudes (>30o), on pole-facing slopes, and shallow (~100m below surface)

• Inferred to be young – cover young features like dunes and polygons

• How do we explain them? Liquid water is not stable at the surface!

• Maybe even active at present day?

Lakes

Titan, 30km across

Clearwater Lakes Canada~30km diameters

Titan lakes are (presumably) methane/ethane

“The Rain on Titan(e) falls mainly as ethane” – Larry Esposito

Glaciation

Perito Moreno Glacier, Patagonia, ArgentinaImage Credit: Luca Galuzzi - www.galuzzi.it

Mars Polar CapImage Credit NASA

Glaciation not terribly common on planets

Icy satellites so cold, ice behaves as rock

Erosion• Erosion will remove small, near-surface craters• But it may also expose (exhume) craters that were

previously buried• Recently recognized as a major process on Mars, but

the details are still extremely poorly understood• Below: Examples of fluvial features which have been

exhumed: the channels are highstanding. Why?

Malin and Edgett, Science 2003

meander

channel

Sediments in outcrop

Opportunity (Meridiani)

Cross-bedding indicative of prolonged fluid flows

Mass Wasting

• Movement of soil, regolith, rock downslope due to gravity• Occurs when gravity exceeds resisting force slope

failure• Downhill creep (slow, minute fluctuations)• Landslides• Flows (e.g. mudslides, avalanches)• Rock falls• Can be triggered by earthquakes, undercutting by

erosion, freeze-thaw.• Does not require an atmosphere

Euler Crater on the Moon (Source: NASA)Terraced crater walls due to slope failure

Ganges Chasma on Mars (Source: NASA)

Devil’s Slide, HWY 1, SF Chronicle

Anim. GIF – U. of Sannio, Italy

Types of Mass WastingNASA

Sputtering

• Bombardment of a material by charged particles (ions) resulting in atoms ejected from surface.

• Important on Asteroids and the Moon

• Why doe the Moon have no atmosphere?

• Much of Mars’ atmosphere sputtered away.

Tectonics on Icy Moons

Iapetus hasA great ridge ‘round the middle

What is up with that?

Miranda – Broken apart and put back together.

Iapetus said to Miranda“You’re really no place for a lander.

Your canyons have rocksLike the teeth on some crocs,

Whereas I’m black and white like a panda.”

Coronae on Venus

Planetary stretch mark.Plume pushing up from below.

Gives YOU stretch marks!Gut pushing out

Yet Another Talk!

Ross Beyer

NASA Ames Research Center

HiRISE views of Martian

Strata and Slope Streaks

Today, 3:30 pmEarth and Marine Sciences (E&MS) Building, Room B210

Tea and snacks in the E&MS Atrium at 3:00PM

Next Time

• Done with Surfaces?– Elastic Flexure?

• Planetary Interiors– Heat Sources– Cooling Mechanisms– Geodynamics– Seismology– Magnetism

• Homework 3 due Monday