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Universal Earth

发布时间:2019-03-07 04:15:03来源:未知点击:

By Eugenie Samuel, San Francisco From the annual meeting of the American Association for the Advancement of Science in San Francisco The rocky material for Earth-like planets is orbiting billions of stars in our galactic neighbourhood, reveals a new stellar survey. It is the first strong evidence implying that planets like ours are commonplace in the Universe. The new data shows that many stars are rich in iron, having gobbled up large numbers of asteroids and comets. These are made from the same material as forms Earth-like planets. If the material is as plentiful as it appears around these stars, it is highly likely to clump together into planets. So far, 53 planets have been identified orbiting other stars but all are gas giants at least the size of Jupiter and moving in unstable and highly eccentric orbits. Some astronomers have used these data to suggest that our solar system is unusual. But the survey of nearby stars by Norman Murray, at the Canadian Institute for Astrophysics at the University of Toronto and his US colleagues, found that over half appear to have been bombarded for billions of years by iron-rich terrestrial material. “This is what happened in our solar system,” he says. “It means the probability that there is life similar to ours is much higher than we thought before the analysis.” But scientists still have no idea of the magnitude of that probability. Murray’s work will prompt astronomers to redouble their efforts to make the first direct detection of an Earth-like planet. “It will happen within a few years now,” said John Percy of the University of Toronto, who was not part of Murray’s collaboration. At the moment there is no way to detect terrestrial planets directly. So Murray and is colleagues searched for indirect effects that Earth-like planets would have on a star. Stars on the “main sequence”, i.e. burning hydrogen, would usually contain less than one per cent iron. But Murray realised that stars in solar systems like ours contain a higher amount of iron. This is because comets and asteroids, about 30 per cent iron by mass, bombard the star over several billion years. The bombardment occurs because of the stable orbits of the planets. They gravitationally perturb the orbits of rocky debris so that it falls into the star, towards the planets themselves or is ejected from the solar system entirely. When Murray and colleagues looked at spectroscopic data on 642 main sequence stars in our galactic neighbourhood, they found a surprisingly high number contained elevated levels of iron in their atmospheres. A statistical analysis based on this data suggests that well over half the stars are being orbited by rocky terrestrial material. The analysis does not say how large the planets are or whether they are orbiting the star in a habitable zone. “We cannot point at any one star and say that has a planet because it is a statistical result” says Murray. If the same statistics are repeated across the galaxy,