Hobbies And Interests
Metis
In 1979, the unmanned space probe, Voyager I, discovered Metis orbiting close to the surface of Jupiter, just inside its main ring. Metis measures 27 miles in diameter, but not much is known about its surface features or characteristics. Astronomers theorize that Metis may be one of the objects that donated material to form Jupiter's main ring. Metis, because of its close proximity to Jupiter, one day will succumb to Jupiter's gravity and collide with the planet.
Atlas, Daphnis and Pan
Atlas, Daphnis and Pan orbit Saturn in nearly perfect circles. All three satellites have non-spherical shapes and lie very near Saturn's outermost A ring. Daphnis is the smallest of the three, measuring a mere 4 miles in diameter. Pan lies closest to the planet, residing within a 200-mile gap between Saturn's rings. Considered "shepherd satellites," these moons keep the gap from closing. Material from Saturn's rings may have come together to form all three moons, which partially may account for their irregular shapes. Because Saturn and its moons pull at the particles making up the rings, the rings appear wavy.
Tethys
The most conspicuous feature on Tethys occurs on the western side of the moon, a gigantic crater called Odysseus, 248 miles in diameter, covering more than a third of the satellite's surface. Such a huge collision should have shattered Tethys at the moment of impact, but the moon continued to exist. Unlike impact craters on other moons and planets, Odysseus is not surrounded by a circular ridge and does not contain a depression at its center. The time Tethys takes to travel around Saturn and the time it takes to rotate once around its axis -- the imaginary north-south line around which a space object revolves -- are exactly the same, about two Earth days.
Portia
In 1986, Voyager II took pictures of Uranus upon passing by the planet. The photos led to the discovery of Portia, a moon with a diameter of 87 miles. Because Uranus lies on its side, Portia, like all of Uranus' satellites, orbits in a north-south direction; in contrast, the moons of other planets move in east-to-west orbits. Portia travels quickly around Uranus, taking less than the length of a day on Earth, whereas Earth's moon takes about a month to make its trip around Earth.
Triton
Scientists theorize that billions of years ago, Neptune's gravity grabbed Triton, the planet's biggest moon, when the two crossed paths. Triton is two times as dense as water, which means that its core contains more rock than the moons of Saturn or Uranus, even though Triton lies farther away from the sun. Unlike other large moons in the solar system, Triton has a retrograde orbit, meaning it orbits Neptune opposite to the way Neptune revolves around its axis. Scientists measure the surface temperature of Triton at approximately -391 degrees Fahrenheit, making Triton the coldest body in the solar system that has been measured thus far.
Despina and Galatea
Discovered in 1989, Despina and Galatea number among two of Neptune's smaller moons, each measuring less than 100 km in average radius. Like many of the smaller moons of the solar system, Galatea and Despina have irregular shapes. Galatea's gravity disrupts the structure of Neptune's rings. Both Despina and Galatea orbit near Neptune's equator. Galatea's orbital eccentricity is about 0.0001 while Despina's is even closer to zero.