Overview Of The Solar System

Joshua Barnes -- Fall 1999

Broadly speaking, the Solar System can be divided into two zones. Bodies in the inner zone are composed of rock and metal, while those in the outer zone consist largely of gas and ice. A somewhat more detailed picture of the Solar System includes:

• Terrestrial Planets: These `Earth-like' planets are found in the inner Solar System. The Earth itself is the largest, followed by Venus, Mars, Mercury, and the Moon.
• Asteroids: Between the orbits of Mars and Jupiter are a vast number of rocky and metallic bodies. The biggest is about 1000 km in diameter, but most are much smaller.
• Jovian Planets: These `Giant' planets are found in the outer Solar System. Jupiter is the largest, followed by Saturn, Neptune, and Uranus.
• Jovian Moons: the giant planets all have multiple moons, which are composed of rock and ice. Ganymede (orbiting Jupiter) and Titan (orbiting Saturn) are the largest.
• Kuiper Belt Objects (KBOs): Beyond the orbit of Neptune we find small icy bodies; Pluto is the largest one known. KBOs which wander into the inner Solar System become comets.

Some basic properties of planets and other objects are listed below:

Planet	Semimajor	Period	Diameter	Mass	Composition	Atmosphere
	axis (AU)	(year)	(km)	(M)
Mercury	0.39	0.24	4878	0.055	metal, rock
Venus	0.72	0.62	12102	0.814	rock, metal	CO2, SO2
Earth	1.00	1.00	12756	1.000	rock, metal	N2, O2, H2O
Moon			3476	0.012	rock
Mars	1.52	1.88	6787	0.107	rock, metal	CO2, N2, Ar
asteroids	2 to 3.5	3 to 6	<1000	small	rock, metal
Jupiter	5.20	11.86	142800	317.5	gas (H, He)	H2, He, CH4, NH3
Ganymede			5262	0.025	ice, rock
Saturn	9.54	29.46	120660	95.1	gas (H, He)	H2, He, CH4, NH3
Titan			5150	0.023	ice, rock	N2, Ar, CH4
Uranus	19.18	84.07	50800	14.5	gas, rock	H2, He, CH4
Neptune	30.06	164.8	50500	17.2	gas, rock	H2, He, CH4
Pluto	39.44	248.6	2300	0.0016	rock, ice?
KBOs	35 to	200 to	<100	tiny	ice, dust

Inner Solar System. In order of increasing distance from the Sun, the orbits of Mercury, Venus, Earth, and Mars, surrounded by the asteroid belt.

Outer Solar System. Left: orbits of Jupiter, Saturn, Uranus, Neptune, Pluto, and a typical comet, surrounded by the Kuiper belt. Right: the Oort cloud, an extended, roughly spherical swarm of KBOs.