据YAHOO报导，两个研究小组排下了第一张太阳系以外的行星照片
WASHINGTON – Earth seems to have its first fuzzy photos of alien planets outside our solar system, images captured by two teams of astronomers. The pictures show four likely planets that appear as specks of white, nearly indecipherable except to the most eagle-eyed experts. All are trillions of miles away — three of them orbiting the same star, and the fourth circling a different star. None of the four giant gaseous planets are remotely habitable or remotely like Earth. But they raise the possibility of others more hospitable. It's only a matter of time before "we get a dot that's blue and Earthlike," said astronomer Bruce Macintosh of the Lawrence Livermore National Lab. He led one of the two teams of photographers. "It is a step on that road to understand if there are other planets like Earth and potentially life out there," he said. Macintosh's team used two ground-based telescopes, while the second team relied on photos from the 18-year-old Hubble Space Telescope to gather images of the exoplanets — planets that don't circle our sun. The research from both teams was published in Thursday's online edition of the journal Science. In the past 13 years, scientists have discovered more than 300 planets outside our solar system, but they have done so indirectly, by measuring changes in gravity, speed or light around stars. NASA's space sciences chief Ed Weiler said the actual photos are important. He compared it to a hunt for elusive elephants: "For years we've been hearing the elephants, finding the tracks, seeing the trees knocked down by them, but we've never been able to snap a picture. Now we have a picture." In a news conference Thursday, Weiler said this fulfills the last of the major goals that NASA had for the Hubble telescope before it launched in 1990: "This is an 18 1/2-year dream come true." There are disputes about whether these are the first exoplanet photos. Others have made earlier claims, but those pictures haven't been confirmed as planets or universally accepted yet. The photos released Thursday are being published in a scientifically prominent journal, but that still hasn't convinced all the experts. Alan Boss, an exoplanet expert at the Carnegie Institution of Washington, and Harvard exoplanet hunter Lisa Kaltenegger both said more study is needed to confirm these photos are proven planets and not just brown dwarf stars. MIT planetary scientist Sara Seager, at the NASA press conference, said earlier planetary claims "are in a gray area." But these discoveries, "everybody would agree is a planet," said Seager, who was not part of either planet-finding team. The Hubble team this spring compared a 2006 photo to one of the same body taken by Hubble in 2004. The scientists used that to show that the object orbited a star and was part of a massive red dust ring which is usually associated with planets — making it less likely to be a dwarf star. Macintosh's team used ground-based telescopes to spot three other planets orbiting a different star. That makes it less likely they are a pack of brown dwarf stars. The planet discovered by Hubble is one of the smallest exoplanets found yet. It's somewhere between the size of Neptune and three times bigger than Jupiter. And it may have a Saturn-like ring. It circles the star Fomalhaut, pronounced FUM-al-HUT, which is Arabic for "mouth of the fish." It's in the constellation Piscis Austrinus and is relatively close by — a mere 148 trillion miles away, practically a next-door neighbor by galactic standards. The planet's temperature is around 260 degrees, but that's cool by comparison to other exoplanets. The planet is only about 200 million years old, a baby compared to the more than 4 billion-year-old planets in our solar system. That's important to astronomers because they can study what Earth and planets in our solar system may have been like in their infancy, said Paul Kalas at the University of California, Berkeley. Kalas led the team using Hubble to discover Fomalhaut's planet. One big reason the picture looks fuzzy is that the star Fomalhaut is 100 million times brighter than its planet. The team led by Macintosh at Lawrence Livermore found its planets a little earlier, spotting the first one in 2007, but taking extra time to confirm the trio of planets circling a star in the Pegasus constellation. They are about 767 trillion miles away, but are actually visible with binoculars. The star in this solar system is HR 8799, and the three planets are seven to 10 times larger than Jupiter, Macintosh said. "I've been doing this for eight years and after eight years we get three at once," he said. |
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