Chapter 6Exploring Terrestrial Surface Processes

and Atmospheres

Terrestrial Planet Surfaces,the Same Yet Different

CratersHeavily cratered areas and smooth low-lying plains

A few thousand, evenly distributed A few hundred

Heavily cratered areas and smooth

low-lying plains

Volcanoes None Many at hot spots, some possibly active

Many active, primarily at plate

boundaries

Many at hot spots, all inactive

Atmosphere None Very thick Just right! Very thin

Impact Craters

• An impactor colliding with the Moon generates a shock wave in the lunar surface that spreads out from the point of impact.

• Produces a nearly perfectly circular crater, no matter in what direction the incoming impactor moves.

• Many of the larger lunar craters also have a central peak, characteristic of a high-speed impact.

Cratering Measures Geologic Activity

• Not all planets and satellites show the same amount of cratering.

• Geological activity erases cratering:– Plate tectonic– Weathering– Erosion

Geologic activity seems to vary with size.

Larger bodies cooled more

slowly, allowing

craters to be erased

Geology of Mercury

• The Caloris Basin, a crater 1300 km (810-mi) in diameter

• The impact fractured the surface extensively, forming several concentric chains of mountains. The mountains in the outermost ring are up to 2 km (6500 ft) high

Cratering recorded gravitational shiftsin the solar system.

Cratering dropped as the solar system “cleared up” then spiked again. Jupiter/Saturn shifting in their orbit?

Heavy Hits During the Late Heavy Bombardment

Some impacts were so intense they weakened the Moon’s crust, leading to cracks where lava welled up and filled the crater.

Tectonics on Venus: A Thin Crust

•y

A Topographic Map of Venus

• Radar altimeter measurements by Magellan were used to produce this topographic map of Venus. Flat plains of volcanic origin cover most of the planet’s surface, with only a few continent like highlands.

• Why can’t we just take pictures?

Tectonics on Mars: A Thick, Rigid Crust

• Mars: no global network of ridges and subduction zones

• The entire crust of Mars makes up a single tectonic plate?

• Magma moving beneath the crust? Magma plumes?

Hot Spots on Mars

• Olympus Mons is the largest volcano in the solar system.• The base of Olympus Mons measures 600 km (370 mi) in

diameter, and the scarps (cliffs) that surround the base are 6 km (4 mi) high.

• The caldera, or volcanic crater, at the summit is approximately 70 km across, large enough to contain the state of Rhode Island.

Valles Marineris• The huge rift valley of

Valles Marineris, 4000 km (2500 mi) long and 600 km (400 mi) wide at its center. Its deepest part is 8 km (5 mi).

• This perspective image from the Mars Express spacecraft shows what you would see from a point high above the central part of Valles Marineris.

A Topographic Map of Mars

• Most of the southern hemisphere is higher than the northern hemisphere.

• The landing sites for probes on Mars are marked with an X.

Volcanoes on Venus, Earth,

and Mars

Plate Tectonics on the Terrestrial Planets

Volcanoes None Many at hot spots, some possibly active

Many active, primarily at plate

boundaries

Many at hot spots, all inactive

Crust Very Very ThickSOLID! Very Thin Just right! Very Thick

Plate Tectonics

No No Yes No

Atmospheres surrounding terrestrialplanets vary considerably.

• These atmospheres all began with materials outgassed by volcanoes.• How did they become so different?

Venus: A Broiled Planet

• Bathed in more intense sunlight than Earth because it is closer to the Sun.

• Too hot to rain liquid water: water is trapped as clouds.

• Water vapor is a greenhouse gas, trapping heat from the Sun.

The Martian Atmosphere: Not a Drop to Drink

CO2 levels dropped, cooling the planet:

runaway icehouse effect

Water may have once existedon the surface of Mars.

• A network of dry riverbeds extending across the cratered southern highlands.

• Teardrop-shaped islands rise above the floor of Ares Valles, carved out by a torrent of water that flowed from the bottom of the image toward the top.

Looking for Water on Our Moon

• SDI-NASA Clementine spacecraft found some evidence of possible ice at the Moon’s poles.

• Lunar Prospector found similar, but still inconclusive, evidence for water.

• LCROSS purposefully crashed into the Moon’s pole and caused an explosive plume of debris to be ejected high above the surface.

• Water was observed among the ejected debris.

Europa: What lies beneath its icy crust?

• Infrared spectrum shows a thin layer of fine-grained water ice frost on top of a surface of pure water ice.

• Jupiter gravitational influence cause “squeezing,” keeping the ocean warm.

Other Signs of an

Underground Ocean