Structure of Mercury And no atmosphere, so no wind or erosion. Surface reflects geologic history well. (from Mariner 10 and theoretical arguments) 1.Crust km thick 2. Mantle 600 km thick 3. Core, 1800 km in radius

Venus Mass = 0.82 M Earth Radius = 0.95 R Earth  Density = 5.2 g/cm 3 Average distance from Sun = 0.72 AU Orbital period = 225 days Rotation period = 243 days (longer than orbital period, and retrograde!)

Venus' Atmosphere - Pressure at surface is 90 x that of Earth's => much more gas in atmosphere. No oceans. - Consequence - meteoroids burn up easily. No impact craters less than ~3 km. What ’ s the composition of the atmosphere? - Hot at surface K! Almost hot enough to melt rock - Why so hot? Huge amount of CO 2 leads to strong greenhouse effect % CO 2 - Yellowish color from sulfuric acid clouds and haze.

Early on, T may have been much lower (but still warmer than Earth). Oceans existed? But if warm enough, T would start to rise because of... Runaway Greenhouse Effect 1) Water and CO 2 evaporate from oceans into atmosphere. 2) Greenhouse effect more efficient. 3) Temperature rises. 4) More evaporation (back to #1). => complete evaporation of oceans. Thick atmosphere.

The Habitable Zone or “The Goldilocks Problem” In the zone …

Missions to Venus Soviet Venera ( ) Mariner 2, 5 and 10 (1962, 1967 and 1974) Pioneer Venus (1978) Magellan (1989) Venera 13 photo of surface. Rocks are basalt and granite. Color is due to atmosphere. Color corrected for atmosphere.

"Radar Echo" technique measures altitude space probe time for signal to return tells you the altitude of surface feature. Planet Surface

Radar data (Pioneer Venus mission) reveal altitude variations on surface. Flatter than Earth, no evidence for plate boundaries => no large scale plate tectonics. 1 km But plenty of evidence of stresses and fractures on smaller scales => much small-scale shifting of crust

Unlike Moon, larger impact craters distributed randomly over surface => all parts of surface have about same age. Paucity of large impact craters => surface is young, million years? Impact Craters

Volcanism Shield volcano elevation map from Magellan radar data. About 100 km across. Volcanism may be ongoing, based on sulfur dioxide variations in atmosphere. But very little resurfacing in past million years. Venus surface flyover

Volcanism Venus surface flight simulation using data from Magellan.

Clicker Question: Why is Venus the hottest planet in the Solar System? A: It is the closest planet to the Sun. B: There is a lot of radioactive material in the crust. C: There is a large concentration of carbon dioxide in the atmosphere. D: The Russians left the lights on in the Venera 5 landing vehicle. E. Paris Hilton lives there.

Mars Mass = 0.11 M Earth Radius = 0.53 R Earth Density = 3.9 g/cm 3 Average distance from Sun = 1.52 AU eccentricity = Range in distance from Sun = AU Rotation Period = 24.6 hours Orbital Period = 687 days

The Martian Atmosphere - 95% CO 2 - Surface Pressure that of Earth's atmosphere (thin air!) - Surface Temperature 250 K. - Dust storms sometimes envelop most of Mars, can last months. A “Reverse Runaway Greenhouse Effect”? During volcanic phase (first two billion years), thicker atmosphere, warmer surface, possibly oceans. Gradually most CO 2 dissolved into surface water and combined with rocks, then atmospheric and surface water froze (creating ice caps and probable permafrost layer).

Mars' Moons Phobos and Deimos Phobos: 28 x 20 km Deimos: 16 x 10 km Properties similar to asteroids. They are probably asteroids captured into orbit by Mars' gravity.

Clicker Question: From Mars, Deimos has an angular diameter of 140 arcseconds. Would colonists on Mars ever see Deimos produce a total solar eclipse? A: Yes, every day on Mars B: Yes, every new moon C: Yes, but rarely D: Never

The Martian Surface Valles Marineris Olympus Mons Tharsis Bulge Southern Hemisphere ~5 km higher elevation than Northern, and more heavily cratered. South is like lunar highlands, surface ~4 billion years old, North like maria, ~3 billion years old. Valles Marineris km long, up to 7 km deep. Ancient crack in crust. Reasons not clear. Tharsis Bulge - highest (10 km) and youngest (2-3 billion years) region. Olympus Mons - shield volcano, highest in Solar System, 3x Everest in height. 100 km across. (Mars Global Surveyor radar data)

View From the Surface Viking 1 site (1976)Sojourner robot from Pathfinder (1997) Dry, desert-like. Red => high iron content. Mars didn't differentiate as completely as Earth. Sky has butterscotch hue due to dust.

Opportunity panorama: inside Victoria Crater Deepest crater explored by far (230 feet) => apparently it was the top of an underground water table.

Evidence for Past Surface Water "runoff channels" or dry rivers "outflow channels" teardrop "islands" in outflow channels standing water erosion in craters? South North

Red arrows: rounded boulders indicating water erosion? White arrows: "conglomerate" rock, like in Earth's riverbeds? Blue arrows: sharp-edged boulders, volcanic rock? Pathfinder site was an outflow channel

Did Mars once have a huge ocean? Long stretches along border are very even in elevation, like a coastline Ocean fed by outflow channels from higher elevation southern hemisphere?

Evidence for "Permafrost" layer beneath surface "Splosh" craters suggesting liquefied ejecta.

Evidence for Water on Mars Now Phoenix Lander (2008) Deployable arm subsurface ice

Phoenix mission – icy soil at the poles! Phoenix analyzing scooped up dirt – was Mars ever favorable for microbial life? Organic compounds?

Mars' History Smaller than Earth, Mars cooled faster. Atmosphere and surface water in first 1.5 billion years. Life? Most volcanic activity ended two billion years ago. Differentiation less complete than on Earth. No evidence for plate tectonics. Atmosphere mostly froze out into subsurface ice, polar ice caps and surface rocks.

Clicker Question: The largest mountain in our solar system is: A: Caloris Basin range on Mercury B: Gula Mons on Venus C: Mt. Everest on Earth D: Olympus Mons on Mars

Clicker Question: Where is the water that once flowed on the surface of Mars? A: In the atmosphere B: In the polar caps only C: In a layer of permafrost below the surface and in the polar caps D: It was diverted to Los Angeles

Martian ‘Snick’ meteorite ALH84001 shows odd shaped features that are reminiscent of bacteria. General consensus is no life.

Valles Marinaris flyover movie

The Face on Mars Viking orbiter photos showed this:

Newer, high resolution photo – Mars Global Surveyor 1998

Isn’t this more disturbing???

Spirit and Opportunity Rovers Scenes from “Roving Mars” (start at 15:10, skip to 20:27, skip to 26:16)