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Observation Jupiter is the biggest planet with an equatorial diameter of 140,000 km, and has a mass 317 times and volume 1323 times that of Earth. Pluto is the smallest planet at a diameter of 2300 kilometer, if you still want to call it a planet (some people call it a Kuiperoid, the largest member of the Kuiper belt). Otherwise the honor goes to Mercury at 4878 kilometers. Ganymede (of Jupiter) is the largest moon, at a diameter of 5262 kilometers. Pluto is the outermost planet orbiting at a mean distance of 5.9 billion kilometers, with an orbital period of 248.54 Earth-years. Mercury is the innermost planet orbiting at a mean distance of 57.9 million kilometers, and an orbital period of 87.97 Earth-days. Pluto is 102 times further out, and has a year 1030 times longer than Mercury. Because of Mercury's short year, it travels in space at 171000 km/h which is 10 times faster than Pluto. The fastest speed humans have travelled at is 39700 km/h with the Apollo 10. Venus's closest approach is 41 million kilometers while Mars' is only 56 million kilometers. Phobos of Mars, is the closest moon to its primary at 9000 kilometers, and Sinope of Jupiter, is the furthest at 23.7 million kilometers. The difference between the two is a factor of 2600. With Phobos, the moon is so close, that eventually it will crash into Mars, while Jupiter is barely capable of keeping Sinope in orbit. Forward to Rotation |