Two planets in unusual star system are very likely habitable, scientists say

时间:2018-01-28 单词数:3760

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Scientists have identified two planets circling round a dim dwarf star as especially likely candidates to have habitable conditions, with probable water and a source of heat, attributes thought necessary for life beyond Earth.


Since their discovery last year, the seven planets and their star, called Trappist-1, have thrilled astronomers hunting for a world resembling Earth. Never before had scientists found so many Earth-sized planets around a single star, or in a zone where the extreme temperatures of space would not obliterate the chances of life.


The finding suggested that there may be planets as rocky and large as Earth all over the Milky Way, and scientists quickly set to work analyzing the Trappist-1 system.


With colleagues in Hungary, Dr Amy Barr of the Planetary Science Institute built mathematical models of the seven planets and their interiors, and found that six of the seven worlds probably have water, as liquid or ice, with a global ocean possible on one. The team then modeled the planets’ orbits to determine a likely surface temperature on the worlds.


“That’s one of the main innovations of the paper,” Barr told the Guardian. “The planets are also on eccentric orbits – kind of egg-shaped – so every time the planet goes around the star it gets stretched and squeezed.”


Barr said, those planets have a “very reasonable surface temperatures”. Planet d, the team estimates, has a temperature around 15C (59F) or perhaps as low as slightly warmer than the melting point of ice. Planet e was colder, Barr said: “the temperatures you would get in Antarctica, but also reasonable”.


The likelihood of tidal heating is encouraging to scientists in search of planets with the conditions for life.


Because Nasa has yet to launch its next-generation space telescope, the James Webb, scientists like Barr and her colleagues have turned to computers to investigate puzzles with limited data.


Should the James Webb launch on schedule this year, it will provide far more data about specific exoplanets.


“It’s hard to write a paper about seven planets all at once,” Barr said.