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| Sunday, 25 September 2005 |
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Junior Observer |  |
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Scientists baffled by hot spot on Saturn's moon : Third active moon discovered?
A hot spot on one of Saturn's moons, which has been recently discovered is yet to be explained. According to space scientists it is located at the south pole of Enceladus, a moon with a diameter of just 310 miles. Scientists consider the hot spot unusual because it occurs at the pole. Usually, the hottest part of any planet or moon is around the equator, as is the case with the Earth. This suggests that the heat at Enceladus' southern pole is generated from within, explains scientists from the Cassini-Huygens mission to Saturn and its moons. But they acknowledged they have no idea as to how this could be. "It shouldn't be that warm," says John Spencer, one of the scientists working on the project. "It's like flying past Antarctica and finding that it's warmer than the earth's equatorial regions. It's that strange." Spencer, of the Southwest Research Institute in Colorado, the United States, is one of a group of scientists examining data sent back to earth from the Cassini spacecraft, which was launched in 1997 to examine Saturn. The spacecraft has flown past Enceladus three times - most recently on July 14. The scientists expected to find that the temperature was around 80 degrees Kelvin (-193 degrees Celsius, -316 degrees Fahrenheit) at its hottest point, which they assumed would be near the equator. Instead, they found that the heat was concentrated at the south pole, where the temperature hit 91 degrees Kelvin near a series of fissures, or "tiger stripes" on the moon's surface. "It is an extremely conspicuous hot region," Spencer told a news conference, recently. "Something is different about that area." The scientists have come up with two theories to explain the hot spot. The first is that the heat comes from decaying radioactive material below the moon's surface, and the second is that it is caused by gravitational tides. But they say neither theory adequately explains the heat. "We don't have anything we could call a complete hypothesis yet," explains Torrence Johnson from NASA, which is working on the project alongside the European and Italian space agencies. The team says the hot spot suggests there might be volcanoes and geysers on Enceladus. If this is true, it would be one of only three "active" moons known to man. The others are Io, which orbits Jupiter, and Triton, which circles Neptune. The Cassini spacecraft has been sending spectacular images back from Saturn, its rings and its moons since last year, when it reached the planet. It also launched a probe which landed on the surface of Titan, another of Saturn's 31 known moons. -Reuters ############## The latest asteroid trio
An asteroid known to astronomers for more than a century has now been found to harbour two small satellites. It is the first asteroid trio ever discovered. And there may be more than three. The main asteroid, named 87 Sylvia, is one of the largest known to orbit the Sun in the main asteroid belt, between Mars and Jupiter. It is potato-shaped, about 175 miles (280 kilometres) in diameter and 235 miles (380 kilometres) long. It was discovered in 1866. The first moon was found four years ago and the second one was announced recently. There are about 60 asteroids known to have one companion each. The first pair was noted in 1993, when the Galileo spacecraft spotted the moonlet Dactyl orbiting asteroid Ida. Some pairs involve a smaller satellite, while in others the two objects are roughly equal in size. Asteroid 87 Sylvia was named for Rhea Sylvia, the mythical mother of the founders of Rome. Now its moons will be called Romulus and Remus, for the ancient city's founders. Romulus is some 11.3 miles (18 kilometres) across and orbits the main asteroid every 87.6 hours. Remus, the newfound object, is about 4.4 miles (7 kilometres) wide and orbits Sylvia every 33 hours. Sylvia completes one rotation about its axis - a day - every 5 hours and 11 minutes. The three-rock setup was likely created in a collision, astronomers said. "People have been looking for multiple asteroid systems for a long time, because binary asteroid systems in the main belt seem to be common and formation scenarios, such as a collision between two asteroids followed by disruption and re-accretion (growth), suggest that fragments should be orbiting bigger asteroids," pointed out Franck Marchis, a researcher at the University of California, Berkeley who led the discovery. There may be smaller moons around Sylvia that still evade detection, explains Marchis. Satellites up to 3 miles (5 kilometres) wide could lurk between the two known moons, he claims and an even larger object could exist inside the orbit of Remus and escape detection. Observations of Sylvia itself support the idea of a collision. The asteroid's low density and known size allowed astronomers to calculate that it must be a rubble pile, rather than a solid rock. "It could be up to 60 per cent empty space," adds French researcher Daniel Hestroffer, a co-author of the study from the Observatoire de Paris. The small satellites are thought to be collision debris that went into orbit rather than getting re-stuck to Sylvia. Based on what they've seen so far, astronomers estimate that about six per cent of asteroids have companions, Marchis says, adding that it is too early to guess how many systems might contain multiple rocks. The discovery was made with a European Southern Observatory telescope in Chile. (Courtesy:space.com) |
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