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Medium & Large Moons: •Enough self-gravity to be spherical Have substantial amounts of ice. •Formed in orbit around jovian planets. •Circular orbits insame direction as planet rotation (except Triton) Small Moons: •Far more numerous than the medium and large moons. •Not enough gravity to be spherical: “potato-shaped” •Captured asteroids or comets The Galilean satelliteswere first seen by the Italian astronomer Galileo Galilei in 1610. Shown from left to right in order of increasing distance from Jupiter, Io is closest, followed by Europa, Ganymede, and Callisto. LOlo had impact craters buried by lavais the closest Galilean satellite to Jupiter, so it has the greatest tidal heating and is the most geologically active moon.Jupiter’s gravity creates tidal bulges on Io. Bulges are largest when Io is nearest Jupiter.Europamay house a deep liquid water ocean Tidal heating not asstrong as on Io, but likely a source of heat for the ocean of water.Ganymede largest moon in solar system Callisto Heavily cratered iceball Furthest of the Galilean moons from Jupiter Titan: A moon with atmosphere Saturn’s largest moon; 2nd largest in the solar system Only moon to have a thick, hazy atmosphere ENCELADUS Plumes of icy material extend above the southern polar region of Saturn's moon Enceladus as imaged by the Cassini spacecraft in February 2005. The monochrome view is presented along with a color-coded version on the right. The latter reveals a fainter and much more extended plume component.Why does Triton orbit Neptune backwards?Triton was captured but its companion escaped It orbits opposite Neptune’s direction of rotation. If Triton had formed with Neptune, it would orbit Neptune in the direction of the planet’s rotation, like all the other large moons in the solar system.Why do the jovian planets have rings? Ring particles are probably debris from moons Meteoroid A bit of interplanetary debris that falls through Earth’s atmosphere Meteor A streak of light caused by a meteoroid Commonly called a “shooting star” MeteoriteA space rock on the ground Meteoroid A bit of interplanetary debris that falls through Earth’s atmosphere Meteor A streak of light caused by a meteoroid Commonly called a “shooting star” Meteorite A space rock on the ground Where do comets come from? Kuiper belt: On more orderly orbits from 30-100 AU in disk of solar system (go around the Sun in the same direction as the planets, roughly in the same plane). Oort cloud: On random orbits extending to about 50,000 AU. Only objects with very elliptical orbits can come into the inner solar system (within the orbit of Neptune). The Oort Cloud is a large spherical cloud with a radius from 50,000 to 100,000 A.U. surrounding the Sun filled with billions to trillions of comets. It has not been directly observed CometNucleus: Mostly water ice, some solid dust; “dirty snowballs” Coma: When a comet nears the Sun, its ices start to vaporize; jets of dust and gas erupt from its surface, which produces a cloud around the nucleus called the coma. Tails: Gas tail - atoms of gases from the comet; Dust tail: smoke-sized particles (smaller than household dust). A comet’s tail always points away from the Sun