Thursday, July 14, 2011

Launch Pad Diary: Very Cool Stuff About Planets

Planets are teeny specks in the middle of nothing, separated by vast distances. 8 major planets with nearly circular orbits; Pluto and Eris are smaller and have more elliptical orbits; Pluto-like objects (many!) Eris is larger than Pluto! (Kuiper belt, objects rocky and icy like comets, 1/2 dozen we know about so far.)

Sun comprises 99.9% of solar system's mass, mostly H/He gas; converts 4 million tons of mass into energy each second.

Mercury - metal and rock, large iron core; desolate, cratered with long, tall steep cliffs, very hot/cold 425oC to -170oC Why iron core: During planetary accretion, lighter elements blown off, only heavier elements left. Outer planets - ices solid, grow bigger and more quickly than inner planets. Jupiter orbit = "frost line" for volatile gases being ice (but we are having to re-think the frost line in light of "hot Jupiters" that orbit very close to their stars.)

Venus - nearly identical to size to Earth, surface hidden by clouds; extreme greenhouse effect, 470oC day and night. High albedo (reflective); SO2, CO2 "greenhouse gases" atmosphere dense, thick, more than makes up for reflective effect of clouds. Extremely slow retrograde rotation, possibly because of impact event.
Greenhouse effect: greenhouse gases keeps earth from being frozen over. Light comes in from sun, is absorbed by earth's surface, radiates thermally about 300 K. Emits infrared radiation at 10 microns. Absorbed in atmosphere by greenhouse gases, like insulating blanket, delays cooling effect. Known since 19th C.
Feedback effects: As temp rises, more water vapor in clouds. If high like cirrus, increases albedo and has cooling effect; if low level clouds, increases absorption and heating. If melt polar caps, get positive feedback loop. Methane frozen under oceans, if released, more efficient greenhouse gas so faster warming.

Earth: oasis of life; only surface liquid water in solar system;

Mars: looks earth-like, giant volcanoes, huge canyon, polar caps (both water and carbon dioxide ice), water in distant past, maybe life? Biggest volcanoe in solar system. Was warmer, had denser atmosphere and surface liquid water. CO2 atmosphere, thin.

Jupiter: mostly H/He, 300 x more massive than Earth; many moons, rings. Don't think there's a solid surface. Galilean moons: Io (active volcanoes, tidal forces produce heating), Europa (possible subsurface ocean 1-2 km below surface, deep volcanic vents, possible site for life), Ganymede (largest moon in solar system), Callisto (cratered "ice ball") - last 2 like Moon.

Saturn: ring system, many moons, including cloudy Titan; tidal forces keep moon from forming at close regions, so get rings, or colliding moons, evidence they are temporary. Titan has atmosphere similar to Earth, liquid hydrocarbons, rain. Rings made of small chunks of ice and rock, each orbiting like a tiny moon, ten meters thick. Have landed probe on Titan.

Uranus, H/He and hydrogen compounds - water, methane, ammonia, extreme axis tilt, moons and ring. May have experienced impact during solar system formation.

Neptune, now celebrating Neptunian year. Many moons incl. Triton (water volcanoes/geysers, water is like lava). Like Uranus except for tilt.

Pluto system, much smaller than major planets, icy and comet-like, Pluto's main moon, Charon, of similar size

All large bodies orbit the Sun in same direction and nearly the same plane; most rotate in same direction. Two types of planets: terrestrial and Jovian planets. Rocky planets are inner system, icey planets outer. Rocky metallic asteroids inner and icy comets outer system. Oort cloud forms circular halo 1 light year across. Exceptions: Uranus tilt, Moon - think there was an impact of a Mars-sized object with Earth, Moon formed from ejecta.

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