{"text":[[{"start":7.05,"text":"Astronomers have for the first time detected an atmosphere around a distant Earth-like planet, in what they called a milestone in the search for life elsewhere in the galaxy."}],[{"start":17.05,"text":"The US-based team identified helium gas escaping from the outer atmosphere of planet LHS 1140b, which orbits a red dwarf star 48 light-years away, far beyond our solar system. "}],[{"start":29.55,"text":"It is what astronomers call a rocky planet, with a solid structure similar to Earth, existing in the ‘habitable zone’ where equable conditions could allow living organisms to evolve."}],[{"start":40.85,"text":"Recent advances in telescope technology have enabled astronomers to analyse exoplanets beyond the solar system for chemical signs of an atmosphere, allowing them to detect one on LHS 1140b nine years after the planet was first discovered."}],[{"start":56.150000000000006,"text":"“An atmosphere is essential for a planet to support life,” said Collin Cherubim, lead author of the study which is published in the journal Science and used instruments at Las Campanas observatory in Chile. “This is the first time anyone has found an atmosphere on a rocky planet in the habitable zone of another star.”"}],[{"start":null,"text":"

"}],[{"start":76.25,"text":"Helium is relatively easy to detect as it is a light gas that tends to rise into the upper layers of a planet’s atmosphere and then escape into space. On Earth, for example, helium dominates the top of the atmosphere, while concentrations at lower altitudes are very small."}],[{"start":93.15,"text":"Over the next few years astronomers will use more powerful instruments, including the James Webb Space Telescope, to probe deeper into the atmosphere of LHS 1140b, trying to determine whether life might have evolved there."}],[{"start":107.35000000000001,"text":"“What is happening below the helium layer is still a mystery,” Cherubim said, “but my model is predicting a more oxidised lower atmosphere rich in things like carbon dioxide, carbon monoxide and even a bit of molecular oxygen. We also believe it should be very water rich.”"}],[{"start":124.25,"text":"The parent star LHS 1140 is around 5bn years old and, like our sun, is very quiet by the standard of most other stars which give off intense bursts of X-rays and ultraviolet radiation. "}],[{"start":139.45,"text":"“This appears to be a clement environment on a rocky planet with an atmosphere in a habitable zone,” said Cherubim. “I think it should be a focus for looking for life outside our solar system.” "}],[{"start":150.35,"text":"The researchers also observed a smaller planet, LHS 1140c, orbiting the same star which had no evidence of an atmosphere. They suggested that the two worlds fall on opposite sides of a “cosmic shoreline”. On one side are planets that retain their atmospheres for billions of years; on the other are ones that are too small or too hot to keep theirs. "}],[{"start":173.79999999999998,"text":"Amaury Triaud, professor of exoplanetology at Birmingham university in the UK who was not involved in the helium discovery, said it “opens up a pathway towards identifying more interesting chemical species. On Earth, geology and biology have a major influence on the chemistry of our atmosphere, and it would be absolutely remarkable to understand this for a temperate rocky exoplanet. Now this looks increasingly feasible.”"}],[{"start":206.09999999999997,"text":""}]],"url":"https://audio.ftcn.net.cn/album/a_1784256298_5215.mp3"}