1. The Solar System Missions

2. planets not shown to scale >> MercuryVenusEarthMarsJupiterSaturnUranusNeptunePluto Mean Distance from the Sun (AU)0.38710.723311.5245.2039.53919.1930.0639.48 Sidereal period of orbit (years)0.240.6211.8811.8629.4684.01164.79248.54 Mean Orbital Velocity (km/sec)47.8935.0429.7924.1413.069.646.815.434.74 Orbital Eccentricity0.2060.0070.0170.0930.0480.0560.0460.0100.248 Inclination to ecliptic (degrees)7.003.4001.851.302.490.771.7717.15 Equatorial Radius (km)2439605263783397714906026825559252691160 Polar Radius (km)same 6357338066854543602497324340same Mass of planet (Earth=1)0.060.8210.11317.8995.1814.5317.140.002 Mean density (grams/centimeter³ )5.435.255.523.951.330.691.291.642.03 Body rotation period (hours)1408583223.9324.629.9210.6617.2416.11153.3 Tilt of equator to orbit (degrees)2177.323.4525.193.1226.7397.8629.6122.46 Number of observed satellites0012>28302481

3. Properties Mass: Planetary masses are determined by measuring the orbital characteristics of moons, or orbiting satellites sent from earth. From Newton’s Laws, the acceleration of the orbiting object (assuming a circular orbit) is From the Universal Law of Gravity a = G {M / r 2 } = v 2 / r where G = 6.67 x 10 -11 Nm 2 /Kg 2 M is the mass of the planet r is the radius of the orbit V is the speed of the orbiting object

4. Properties Mass: Planetary masses are determined by measuring the orbital characteristics of moons, or orbiting satellites sent from earth. From Newton’s Laws, the acceleration of the orbiting object (assuming a circular orbit) is Note: the speed can easily be determined from knowledge of the radius of the orbit and the period. In one period, the object must travel a distance equal to the circumference of the orbit: v = 2  r / T where 2  r is the circumference of the orbit T is the period

5. Properties Mass: Planetary masses are determined by measuring the orbital characteristics of moons, or orbiting satellites sent from earth. From Newton’s Laws, the acceleration of the orbiting object (assuming a circular orbit) is Therefore: M = r v 2 / G where G = 6.67 x 10 -11 Nm 2 /Kg 2 M is the mass of the planet r is the radius of the orbit

6. Properties Density: Once the mass of the planet is known, the density is computed from the calculated mass and the observed angular size of the object. d = m / V where D is the density V is the volume

7. Properties Atmosphere: Existence determined by a tradeoff between the gravitation attraction on particles and the speed of the particles (based upon the their temperature).

8. Properties Water: Big current question. Answers to the existence of water on planets and moons is under active investigation.