1. The Solar System Missions

2. Comparative Planetology * The study of the similarities and dissimilarities of the constituents of the solar system. * Provides a basis for understanding how the solar system might have formed and how it evolved.

3. 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

4. Properties Mass: Planetary masses are determined by measuring the orbital characteristics of moons, orbital characteristics of comets or asteroids, effects on the orbits of other planets, 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

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 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 π r / T where 2 π r is the circumference of the orbit T is the period

6. 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

7. 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

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

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