Anthony Pezzo, Jr., age 12, of St. Louis, Missouri, for his question:
How fast do the different planets rotate?
The planets are spherical, more or less, and each rotates around its central axis. Each spin turns first one half of its globe to face the sun, then the opposite side. Hence, rotation speed determines the length of a planet's day and night period. Our nine planets are different sizes and each rotates at its own speed. For example, Mars takes about 12 hours and 15 minutes to rotate from noon to midnight. And while we are rotating through the morning hours, giant Jupiter spins from dawn to sunset.
We might expect the giant planets to take longer to complete each rotation because their bulging equators must spin around larger circles. But this is not so. The rotation speed of most, but not all, of them has been measured and of those we know, the fastest spinner is Jupiter. The diameter of its equator is 88,770 miles and its size is big enough to engulf the other eight planets.
Giant Jupiter completes its revolution in about ten earth hours, which gives each half of the enormous globe five hours of daylight and five hours of darkness. At the Jovian equator, where the spin is fastest, rotation speed must be more than 25,000 miles per hour.
Saturn is almost ten times wider than the earth and its volume is 736 times greater. As with other planets, rotation is estimated by the motion of surface features. Saturn's equator rotates in ten hours and 13 minutes. Surface spots indicate that the daily rotation lads between the equator and the poles.
The diameter of Uranus is 29,000 miles, which makes its volume more than 60 times greater than the earth's. Its rotation period is ten hours and 49 minutes. Neptune is about 60 times larger than the earth and its day and night rotation period is estimated to be 15 hours and 40 minutes. Our present figures may not be perfect but most certainly the big planets are the fast spinners.
Closer to home is little :iars, only 4,200 miles wide. Its rotation period is 24 hours and 37 minutes. At the Martian equator, rotation speed is about 530 miles per hour and the riartian calendar day is about half an hour longer than ours. Our other neighbor is golden Venus, almost a twin in size. Dense clouds conceal its surface and rotation is difficult to detect. According to recent estimates, the earth spins through 243 calendar days while Venus is completing one rotation.
Mercury is closest to the sun and Pluto is way out there at the edge of the Solar System. Astronomers still are clocking their rotation period. Mercury is a fairly slow spinner and Pluto is fairly fast.
According to recent estimates, 'Mercury day files around one rotation period while the earth completes 59 which is almost two earth months. The rotation period of little Pluto is estimated to be 6 earth days, or less than a week. The figures on Mercury, Pluto and Venus may be revised. More sophisticated techniques are expected to clock their spinning surfaces in finer detail.
For more information on planet statistics go to: http://www.windows.ucar.edu/tour/link=/our_solar_system/solar_system.html