Terrestrial Planet Surfaces How do they compare to

Terrestrial Planet Surfaces How do they compare to one another?

Lets Play “Guess Which Surface is which? ” Mercury The Moon

Hmm…Mars? Venus

Home Sweet Home!

Comparison of Planetary Surfaces • Mercury & the Moon • heavily cratered {scars from the heavy bombardment} • some volcanic plains • Venus • volcanoes and bizarre bulges • Mars • volcanoes and canyons • apparently dry riverbeds {evidence for running water? } • Earth • all of the above plus liquid water and life

Geological Destiny A planet’s fundamental properties determine its geological fate. • Impact cratering • important early on • affects all planets equally • Volcanism & Tectonics • become dominant later on • require internal heat • size determines how long a planet remains hot • Erosion planet size determines fate • ultimately dominant • requires volcanism for outgassing of atmosphere

Inside the Terrestrial Worlds • After they have formed, the molten planets differentiate into three zones: • core - made of metals • mantle - made of dense rock • crust - made of less dense rock • Lithosphere - the rigid, outer layer of crust & part of the mantle which does not deform easily

Inside the Terrestrial Worlds

Inside the Terrestrial Worlds active geology inactive geology

Image from: http: //www. washington. edu/burkemuseum/ geo_history_wa/ • Planetary interiors heat up through: • accretion • differentiation • radioactivity Supplies all the heat at the beginning Supplies heat throughout the planet’s life As mass “falls” inward, gravitational energy is converted to random kinetic energy—this is the famous “helmoltz mechanisim”

Cooling the Terrestrial Worlds • Planets cool off through: • conduction - heat flowing on the microscopic level • convection - heat flowing on the macroscopic level (bulk motions) • eruptions – a violent form of convection--hot lava bursts through crust • Cooling also occurs through radiation (but much slower than the other mechanisms)

Cooling the Terrestrial Worlds

• • • Geometry of Cooling! Heat escapes through surface area Heat is retained by volume Ratio of Area to volume Determines rate of cooling –smaller means faster cooling! V=Lx. L A=Lx. L A/V = 1/L Here L = 3 cm, so A/V = 1/3 What about a smaller cube, 1 cm on a side? A/V = 1/1 so it will cool three times faster (or hot 1/3 as long)

Rate of cooling depends on Radius Heat is contained with Volume but passes out through surface The ratio of Area to volume = 3/R (Similar to Cube L -> R) The smaller the Radius, the more area there is compared with volume Mars half the radius of Earth, so it cools off twice as fast!

Impact Cratering • objects hit planet at 10 – 70 km/s • solid rock is vaporized • a crater is excavated • The diameter of crater is about ten times the size of the impactor • craters are circular – large craters have a central peak

Counting Craters to find Surface Age • Cratering rate decreased as Solar Systems aged. • The older the surface, the more craters are present.

Tectonics • convection cells in the mantle causes both: • compression in lithosphere • mountains are produced • extension in lithosphere • valleys are produced • mountains & valleys appear on the surface

Erosion • movement of rock by ice, liquid, or gas • valleys shaped by glaciers • canyons carved by rivers • sand blown by wind • erosion not only wears down features, it also builds them: • sand dunes • river deltas • sedimentary rock

Volcanism • Underground, molten rock, called magma, breaks through crack in the lithosphere. • Trapped gases are released: • H 2 O, CO 2, N 2 • Viscosity of lava (typically basalt) determines type of volcano

Volcanoes Volcano Arenal—Costa Rican Stratovolcano (image from: www. adventure-inn. com)

Shield Volcano Mauna Kea on Hawaii…note moonrise through shadow!

Shield Volcanoes can grow to great size over hotspots Hawaii—Mauna Loa and Mauna Kea—Kilauea in Red

Atmosphere is formed from outgassing • This sounds subtle but it isn’t!

Mars • Olympus Mons • the largest volcano in our Solar System • it is located atop the Tharsis Bulge along with several other volcanoes Martian Atmosphere outgassed just like Earth’s —primarily CO 2 , H 2 O and SO 2, and N 2 Martian Pressure is 1/180 of Earth’s pressure. . so where did all the air go?

Volcanism on Venus • Highest Volcano is Maxwell (17 km high)—plenty of sources of outgassing • Pancake Volcano are common • Atmospheric pressure is 90 x earth’s pressure! • Venus doesn’t have a true crust since its still in the Oven!