11. Venus and Mars

Mass = 0.82 Mearth

Radius = 0.95 Rearth

Density: ρ= 5.2 g/cm3 (Earth 5.5 g/cm3)

Gravity = 0.90 that of Earth

Average distance from Sun = 0.72 AU

Orbital period = 225 days

Rotation period = 243 days (longer than orbital period, and retrograde!)

Venus

The density of craters suggests that the entire surface of Venus is no more than a few hundred million years old.

According to the equilibrium resurfacing hypothesis, this happens because old craters are erased by ongoing volcanic eruptions

Volcanoes on Venus

• Convection in its mantle generated great stresses in the crust of Venus, though no continental plate movement.

• The formation of lava plains of Venus more nearly resembles that of the lunar maria.

Venus has a hot, dense atmosphere and corrosivecloud layers

• The surface pressure on Venus is 90 bar, and the surface temperature is 460°C (860oF)

• Venus’s clouds consist of droplets of concentrated sulfuric acid.

•Weather remains perpetually hot and dry, with calm winds

H2O

Runaway Greenhouse Effect

•Venus and Earth most likely had similar initial conditions•moderate temperatures •water oceans• CO2 dissolved in the ocean or rocks

•Venus is closer to the Sun thus would have hotter surface temperatures.•More H2O and CO2 (Greenhouse gases) are

vaporized into the atmosphere because of hotter surface.•A thicker atmosphere traps more heat from the Sun, more Greenhouse gases are produced.

Where did the H2O go?

•Venus's surface got so hot that all liquid water evaporated.• No mechanism for storing CO2

•Ultraviolet light interacts with the H2O separating the molecule.

•Hydrogen is light and escapes the planets gravity.

•Oxygen combines with surface rock.

•No water means no way of decreasing the amount of CO2.

• Is this Earth’s fate?

Mars

Mass = 0.11 Mearth

Radius = 0.53 Rearth

Density: ρ= 2.9 g/cm3

(Earth 5.5 g/cm3)

Range in distance from Sun = 1.38-1.66 AU

Eccentricity = 0.093

Orbital period = 687 days (1.9 years)

Rotation period = 24.6 hours

Gravity 0.38*gearth

Mars

The Martian Surface

Volcanoes on Mars

• 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.

•Highland area is the location of many volcanoes.•Mount Olympus is the largest mountain in the solar

system.

•Based on cratering on Mount Olympus, the volcano is young (100- 1000’s of years old).

•Tectonic cracking occurred too creating massive canyons! (Valles Marineris)

Olympus Mons

Valles Marineris

Sojourner robot from Pathfinder (1997)

• Dry, desert-like. Red => high in iron content.• Mars didn’t differentiate as completely as Earth. • Sky has butterscotch hue due to dust.

Mosaic of many images from Curiosity (2013) in the Gale crater

Surface of Mars

•Summer temps 240-190 Kelvin.

•Cold enough to freeze CO2

•Massive temperature changes can cause HUGE dust storms.

•CO2 cloud cover can form similar to H2O Earth clouds.

The Polar Caps

• Poles grow and shrink just like Earth.

• CO2 ice changes with seasons.

•H2O is permanently frozen at the poles and does not experience seasonal changes.

• Liquid water cannot exist on the surface because it is too cold and the pressure is too low.

Evidence for Past Surface Water

"runoff channels" or dry rivers

"outflow channels"

teardrop "islands" in outflow channels

standing water erosion in craters?

Evidence for “Permafrost” layer beneath surface

Splosh craters suggesting liquefied ejecta.

Evidence for Water on Mars Now

Phoenix Lander (2008) Deployable arm

subsurface ice

Did Mars once have a huge ocean?

Long stretches along border are very even in elevation, like a coastline

Ocean fed by outflow channels fromhigher elevation southern hemisphere?

Mars’ Moons Phobos and Deimos

Phobos: 28 x 20 kmMass = 1.08 x 1016 g

Deimos: 16 x 10 kmMass = 1.48 x 1015 g

Properties similar to asteroids. They are probably asteroids captured into orbit by Mars' gravity.

Discovered in 1877 by Asaph Hall

Run away reverse greenhouse effect

•Early Mars probably had enough CO2 to be warmed by the Greenhouse effect.

• Lower gravity meant that the atmosphere could escape more easily.

• Less volcanic activity meant less CO2 was produced.

•As temperatures dropped, water froze.

•Comet impacts might provide a thick enough atmosphere to temporally create an insulating atmosphere.

Life on Mars

•Earth life needs liquid water.

•Life as we know it probably doesn’t exists on Mars TODAY.

•Mars most likely had liquid water at some point in its past.

•Mars probes are now looking for fossils of past life on Mars.