Astronomers1 searching the atmospheres of alien worlds for gases that might be produced by life cant rely on the detection of just one type, such as oxygen, ozone3, or methane4, because in some cases these gases can be produced non-biologically, according to extensive simulations by researchers in the NASA Astrobiology Institutes Virtual Planetary Laboratory. The researchers carefully simulated the atmospheric5 chemistry of alien worlds devoid6 of life thousands of times over a period of more than four years, varying the atmospheric compositions and star types. When we ran these calculations, we found that in some cases, there was a significant amount of ozone that built up in the atmosphere, despite there not being any oxygen flowing into the atmosphere, said Shawn Domagal-Goldman of NASAs Goddard Space Flight Center in Greenbelt, Maryland. This has important implications for our future plans to look for life beyond Earth.Methane is a carbon atom bound to four hydrogen atoms. On Earth, much of it is produced biologically , but it can also be made inorganically7; for example, volcanoes at the bottom of the ocean can release the gas after it is produced by reactions of rocks with seawater.Ozone and oxygen were previously8 thought to be stronger biosignatures on their own. Ozone is three atoms of oxygen bound together. On Earth, it is produced when molecular9 oxygen and atomic oxygen combine, after the atomic oxygen is created by other reactions powered by sunlight or lightning. Life is the dominant10 source of the molecular oxygen on our planet, as the gas is produced by photosynthesis11 in plants and microscopic12, single-cell organisms. Because life dominates the production of oxygen, and oxygen is needed for ozone, both gases were thought to be relatively13 strong biosignatures. But this study demonstrated that both molecular oxygen and ozone can be made without life when ultraviolet light breaks apart carbon dioxide . Their research suggests this non-biological process could create enough ozone for it to be detectable14 across space, so the detection of ozone by itself would not be a definitive15 sign of life.However, our research strengthens the argument that methane and oxygen together, or methane and ozone together, are still strong signatures of life, said Domagal-Goldman. We tried really, really hard to make false-positive signals for life, and we did find some, but only for oxygen, ozone, or methane by themselves. Domagal-Goldman and Antgona Segura from the Universidad Nacional Autnoma de Mxico in Mexico City are lead authors of a paper about this research, along with astronomer2 Victoria Meadows, geologist16 Mark Claire, and Tyler Robison, an expert on what Earth would look like as an extrasolar planet. The paper appeared in the Astrophysical Journal Sept. 10, and is available online.
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1 astronomers n.天文学者，天文学家 参考例句： Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告将来日食月食的日期、时刻和时长。 来自《简明英汉词典》 Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为何只有土星有光环。 来自《简明英汉词典》
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