Longer days and nights would lead to greater temperature differences between day and night if the Earth rotated more slowly. Jupiter and Saturn have the most moons. Europa, a moon of Jupiter, may support life as it contains water ice. The Magellan spacecraft mapped the surface of Venus while the Galileo spacecraft mapped Jupiter and its moons. Mars, Earth, Saturn and the Moon are described based on their physical characteristics. Pluto was demoted to a dwarf planet. Meteors and meteorites are small pieces of debris burning up in the atmosphere. Uranus is described as having blue-green clouds and rings when viewed through a telescope. Asteroids orbit between Mars and Jupiter. Venus' thick, cloudy atmosphere makes its