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Inside-Out Study Challenges Theory About Comet Chemistry
Paris (AFP) July 11, 2007 A dying comet has prompted astronomers to take issue with a mainstream theory about the impact of "space weather" on these enigmatic wanderers of the Solar System. Comets are fragile clusters of dust, ice and carbon-based molecules that are believed to be primitive material left over from the building of our star system. A common expectation is that the outer layers of comets must undergo change as the aeons pass. They are bashed by cosmic rays from deep space, by solar particles and by huge changes in temperature as they swing around the Sun and head back into the chilly depths of the Solar System. In theory, this "weathering" should be especially pronounced in so-called short-period comets, which return every few years, as opposed to counterparts that can take centuries to loop around the Sun. But astronomers in the United States, seizing a unique chance after a short-period comet broke up, say cometary chemistry appears to be the same, inside and out. They looked at Comet 73P/Schwassmann-Wachmann 3 -- 73P for short -- which returns around the Sun every 5.3 years. In 1995, 73P experienced a catastrophic breakup, disintegrating into 68 large fragments, two of which were hundreds of metres (yards) across. Last year, 73P, escorted by its disparate family, zipped by close to Earth, enabling the astronomers to glimpse the chemical composition of the two big chunks, using spectrometers at the giant observatory at Mauna Kea, Hawaii. They found that, unlike most comets, the fragments were low in complex volatile ices, such as acetylene, methanol and ammonia, which suggests they were unusually primordial in origin. And contrary to expectation, the fragments were found to be chemically very similar, inside and externally, which challenges the weathering theory. The paper, led by Johns Hopkins University's Neil Dello Russo, appears in Thursday's Nature, the weekly British science journal.
Source: Agence France-Presse Community Email This Article Comment On This Article Related Links Johns Hopkins University Asteroid and Comet Mission News, Science and Technology
NASA Delays Dawn Asteroid Probe Launch Until September
Washington (AFP) Jul 09, 2007The US space agency has postponed until September the launch of space probe Dawn on its eight-year mission to unlock the mysteries of the origins of our solar system. It was the second delay for the mission in as many days. "Primary reasons for the move were a combination of highly limited launch opportunities for Dawn in July and the potential impact to launch preparations for the upcoming Phoenix Mars Lander mission, set for early August," the National Aeronautics and Space Administration said in a statement Saturday. |
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