笔译二级实务（综合）模拟试卷37
必做题
1. On earth, most of the methane in the atmosphere has been belched by living organisms, so finding the gas on Mars would J be happy news for seekers after extraterrestrial life. Sadly, news announced on December 12th, at the annual meeting of the American Geophysical Union (AGU), in Washington, DC, was anything but happy. Preliminary results from ExoMars Trace Gas Orbiter, a European craft that has been circling Mars for the past two years, give a thumbs-down to the idea that there is methane in its atmosphere.
Previous observations, from orbit and by telescopes on Earth, suggested Mars might spot traces of the gas. These were backed up by data from Curiosity, an American Mars rover. In its six years crawling around a crater called Gale, Curiosity has both detected methane and recorded seasonal ups and downs of the stuff that cycle from a modest 0.25 parts per billion during the winter to 0.65 ppbn in the summer, with spikes up to 7.0 ppbn.
That cyclical pattern has intrigued researchers back on Earth. Broadly speaking, there are two possible sources for Martian methane. One is outer space, whence carbon-rich molecules, some of which are likely to break down into methane, arrive constantly on meteors of various sizes. The other is from under the planet’s surface.
Methane from both sources will mix eventually into the atmosphere. But if the gas is coming from underground, it will be more concentrated near its source, and might well appear on a seasonal basis. The process could be a geological or geochemical one that is encouraged by the relative warmth of summer. That would be interesting. Or it could be biological, with methane-generating bugs waking up during the summer months. For either to be the explanation of the seasonality observed by Curiosity, the rover would have to have had the luck to land in an area of such methane seeps. But such lucky breaks do happen.
Regardless of their source, any methane molecules in Mars’s atmosphere would, on the basis of experiments on Earth, be expected to hang around for centuries. It was to find signs of this more widespread material that a spectroscopic instrument called NOMAD (Nadir and Occultation for Mars Discovery), which is on board ExoMars Trace Gas Orbiter, was designed. And, it has failed to find the slightest hint of methane in the Martian atmosphere. Since NOMAD is 20 times more sensitive than the methane detector on board Curiosity, this is bad news.
But they do not surprise Kevin Zahnle of the Ames Research Centre, in California, a laboratory belonging to NASA, America’s space agency. Dr Zahnle has long argued that Curiosity’s reports of Martian methane are artefacts.
The optimists will not be deflected, though. They note that NOMAD can probe only the upper part of Mars’s atmosphere. Air with an altitude of less than 5 km is beyond its range. Moreover, when ExoMars Trace Gas Orbiter flew over Gale, a dust storm obscured NOMAD’s view of anything within 30 km of the surface. What NOMAD does seem to show is that, if methane exists at all in Mars’s air, it is rare and confined to low levels of the atmosphere. But for now, neither side is willing to give way.
地球大气中大部分的甲烷是由生物释放出来的，所以在火星上发现甲烷气体对于寻找外星生命的科学家来说无疑是个好消息。然而，12月12日，在华盛顿特区举行的美国地球物理联盟(AGU)年度会议上发布了一则令人沮丧的新闻。环绕火星飞行两年之久的欧洲航天器火星微量气体任务卫星 (ExoMars Trace Gas Orbiter
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