1.25: Planets and Planetary Systems of the Solar System

A planet is a large spherical celestial body moving in an elliptical orbit around a star. A planetary system is a set of gravitationally bound celestial objects in orbit around a star or star system. Planets with orbiting moons are planetary systems. The Solar System consists of four inner rocky planets, four outer gas planets, and orbiting belts of asteroids, comets, planetesimals, and other objects under the gravitation influence of the Sun.

The 4 Inner Rocky Planets
Figure 1.65. Mercury	Figure 1.66. Venus	Figure 1.67. Earth	Figure 1.68. Mars
a rocky planet no atmosphere no moons planet radius: 1,516 miles (2440 km) average distance from sun: 36 million miles (58 million km) orbital period: 88 days gravity: 3.7 m/sec2	a rocky planet hot atmosphere, mostly CO2 (with a sulfur-rich cloud cover) no moons planet radius: 3,760 miles (6050 km) average distance from sun: 67.24 million miles (108 million km) rotation (day): -243 day (it rotates backwards!) orbital period: 224.7 days gravity: 8.87 m/sec^2	a rocky planet with oceans, ice cap, and atmosphere supports life! one moon (the Moon!) planet radius: 3,959 miles (6370 km) average distance from sun: 92.96 million miles (150 million km) rotation (day): 24 hours orbital period: 365.24 days gravity: 9.8 m/sec^2	a rocky planet has ice caps at poles thin atmosphere, mostly CO2 2 small moons: (Phobos and Deimos) planet radius: 2,106 miles (3390 km) average distance from sun: 141.6 million miles (228 million km) rotation (day) 24.67 hours orbital period: 687 days gravity:

The 4 Outer Gas Planets (or Planetary Systems)
Figure 1.69. Jupiter	Figure 1.70. Saturn	Figure 1.71. Uranus	Figure 1.72. Neptune
largest of the gas planets mostly hydrogen and helium has 67 moons, of which 4 are much larger than other moons. very active storms are visible in its atmosphere. planet radius: 43,441 mile 70,000 km) *average distance from sun: 483.8 million miles (779 million km) orbital period: 12 years rotation (day): 9 hr, 56 min	a gas planet famous for its visible rings (mostly dust, ice, and rock fragments). Currently has 62 moons, including Titan, the largest in the Solar System. planet radius: 36,184 miles (36,200 km) average distance from sun: 888.2 million miles (1.42 billion km) orbital period: 29 years rotation (day): 10 hr, 42 min	a gas planet has 5 medium-sized moons (many smaller ones too) planet radius:15,759 miles (25,400 km) average distance from sun: 1.784 billion miles (2.87 billion km) orbital period: 84 years rotation (day): 17 hr, 14 min	the outermost gas planet has 13 known moons planet radius: 15,299 miles (24,620 km) average distance from sun: 2.795 billion miles (4.5 billion km) orbital period: 165 years rotation (day): 16 hr, 6 min