Forming Stars and Planets II
& Our Solar System

	Lecture 14 Ay-1

Lecture 11: Summary

	all planets (terrestrial & Jovian) orbit Sun counterclockwise
	system extends to ~ 10,000 AU (Oort cloud)
	most orbits ~ circular & close to ecliptic plane
	planetary motions follow Kepler’s laws
	1 AU  = 1.5 x 1013 cm  (or 149,597,870 km)
	solar system formed 4.6 Byrs ago in a rotating,
	circumstellar disk of gas and dust
	follow evolution by observing sources at different epochs

planet-forming disks in Orion
stars £ 1 Myr

HR 4796: age ~ 10 Myrs

	A0 star ( 2 M¤) at 67 pc
	dust ring width ~ 17 AU, radius 70 AU
	collisionally-produced debris?

b Pictoris ~ 20 Myrs

Vega :  350 Myrs

Epsilon Eridani :  ~ 0.5 -1 Byr

	distance  ~ 10 lyrs
	850 mm dust emission            ® ring, mass ~ 0.2 MÅ
	inner radius 35 AU              ~ Neptune’s orbit
	outer radius 75 AU              ~ Kuiper Belt

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CARMA
Combined Array for Research in mm-wave Astronomy

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Condensation sequence :

Venus

Planetary radiative equilibrium

	Energy absorbed = Energy radiated
	(L/(4pd2))pr2 = 4pr2sT4
	T = 278 (L¤/d2AU)1/4 K
	Greenhouse effect :
	Earth’s atmosphere relatively transparent to solar  radiation (heating)
	but re-radiation (cooling) in infrared is impeded (photons absorbed by CO2, H2O)
	For Venus, greenhouse effect is enormous
	due to CO2, T = 600K  (could happen at Earth)

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Saturn

	density 0.69 gm/cc
	belt zones like Jupiter but under a methane haze and less visible
	24 moons - cause gaps in rings due to gravitational perturbations
		Titan largest ~ Mercury mass
		1.5 x moon atmosphere; methane and nitrogen smog
		surface cold - ice (179K); reverse greenhouse effect - smog blocks sunlight

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