Planets and their satellites Flashcards
Inner planets
Mercury, Venus, Earth, Mars
Differentiated bodies with silicate mantles and crusts and iron-nickel cores
Moon
Visible from Earth:
White areas are the highland, cratered regions. Igneous rocks 4.0-4.6 Ga dominated by plagioclase.
Darker areas are smoother mare. Young basalt with a mean age of 3.8Ga
Volcanism and tectonic activity stopped 2.5-3.0 Ga.
Cooled quicker than Earth due to greater SA:Volume and 1/100 the mass of Earth so always contained less radioactive isotopes.
Since there’s no regeneration of the moon’s surface by plate tectonics, it has maintained a record of bombardment by meteorites and is heavily cratered. Craters are up to 1000km in diameter. Crater-size shows that heavy bombardment occurred from moon’s formation to 3.8Ga.
Moon is differentiated like inner planets. Potassium and Uranium relative abundance shows that there’s depletion of volatile elements on the moon. The original nebula the solar system came from would have greater K:U ratio. Potassium and Uranium aren’t found in common minerals. So, their abundance is unaffected by the differentiation process i.e. surface reflects abundance throughout. Moon is more depleted in K than Earth.
Ratio of K41:K39 is the same on the moon as on all other other planets. Volatiles evaporated before individual bodies formed.
Mars
Radius is half of Earth’s
g is 1/3 of Earth’s
Melting occurs due to adiabatic decompression, so starts at greater depths on Mars and more melt is generated.
The largest volcano in the solar system is on Mars: Olympus Mons. Summit 24km above base, 600km width and 100 times the volume of the largest volcano on Earth.
Heat production scales with r^3 while heat loss scales with r^2. Therefore, the lithospheric thickness scales with 1/r and on Mars is probably double that of Earth’s.
Average surface temperature: -60 degrees celsius
Ice found in crater walls and on CO2 ice caps
Possible evidence of rivers and shorelines. Probable that in the past there was lots of liquid water on Mars.
No organised plate tectonic system.
Atmosphere is thin (1/50th the pressure on Earth) and gravity field is week. Meteorites knock off portions and these become martian meteorites.
Basaltic breccias with glass that traps bubbles of atmosphere. N14/N15 ratio is 170 compared to 272 on Earth. So on Mars the atmosphere fractionates. Velocity of molecules must reach escape velocity which depends on Martian gravitational field and molecules must have a mean free path. Meteorites also contain hydrated minerals: proof of water
Venus
Surface temperature: 450 degrees celsius
Atmosphere of CO2 and sulfuric acid. Surface pressure 90 times Earth’s.
No surface water and insignificant amount in atmosphere.
Image through dense atmosphere with radar - done by Magellan.
Impact craters visible –> only large meteorites penetrate the atmosphere. Density of impact craters used to estimate average age of the surface (500Ma), comparable to Earth. But, average age is the same all across its surface; so, debate over tectonic activity.
Pancakes are structures probably from viscous rhyolitic magma. But no explosive volcanism due to high pressure atmosphere and low water content of magma.
Deformation like on Earth. Gravity anomalies coincide with structures supported by elastic deformation.
Io
Moon of Jupiter
Density and size between Earth and Mars
Orbital resonance keeps interior hot enough to cause melting
Observed eruption plumes up to 300km high - probably sulfur and silicate
Europa
Moon of Jupiter
Cracked surface of mostly ice
Half the density of the moon
At least 5% water
Ice may be a rigid lithosphere like layer above a molten centre kept hot by tidal heating.
Crack pattern and lack of impact crater suggest tectonic activity.
Enceladus
Moon of Saturn
Icy planet with old, cratered terrain overlain by young, smooth areas that haven’t accumulated craters yet.
Shiny – maybe sparkling of fresh ice eruptions (observed ice and water vapour plumes)
May be an ocean of liquid water below cracks
Miranda
Moon of Uranus
very densely cratered –> probably inactive
Extrusions of ice
Triton
Moon of neptune
Polar cap of frozen nitrogen
Plumes of dust up to 8km
Mostly water-ice with frozen methane and ammonia
