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.)
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Extrasolar Planets

Stars orbit the center of mass of their systems (not center of star mass); hence, planets can perturb a star's orbit. Stars wobble due to tiny gravitational effects of their planets (meters per second). Look for shifts in the absorption spectra; from the period and size of the shift, we can determine the mass of an object affecting a star. A star's motion can be influenced by multiple planets, but it is still possible to determine their masses and orbits. Detecting these very tiny shifts requires precision technology.

Astrometric technique; we can detect planets by measuring changes in star's position.

Doppler shifts detected in the spectroscopic analysis of 51 Pegasi indirectly revealed a planet with 4 day orbit (50 m/sec). Rapid period means the orbit is small and the planet is close to the star. Discovered 1995. Mass similar to Jupiter but within radius of Mercury. This class of planets are called "hot Jupiters."
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