so finding the gas on Mars would be happy news for seekers after extraterrestrial life. 所以对探求者们来说，在火星上发现气体是仅次于发现地外生命的好消息。

Sadly, news announced on December 12th, at the annual meeting of the American Geophysical Union (AGU), in Washington, DC, was anything but happy. 不幸的是，12月12日在华盛顿特区举行的美国地球物理学会（AGU）年度会议上宣布的消息却让人开心不起来。

Preliminary results from ExoMars Trace Gas Orbiter, a European craft that has been circling Mars for the past two years, 欧洲的ExoMars微量气体探测轨道飞行器在过去两年中一直围绕火星盘旋，

give a thumbs-down to the idea that there is methane in its atmosphere. 该飞船发回的初步结果与火星大气中有甲烷的说法相悖。

Previous observations, from orbit and by telescopes on Earth, suggested Mars might sport traces of the gas. 从轨道发回的以及从地球望远镜中观察到的早期观察结果表明火星上或许有气体存在的痕迹。

These were backed up by data from Curiosity, an American Mars rover. 这些都得到了美国火星探测车好奇号的数据支撑。

In its six years crawling around a crater called Gale Curiosity has both detected methane 在六年的时间里，它一直围绕着盖尔环形山爬行，好奇号既探测到了甲烷

and recorded seasonal ups and downs of the stuff that cycle from a modest 0.25 parts per billion during the winter to 0.65ppbn in the summer, with spikes up to 7.0ppbn. 也记录下了这种物质季节性的波动，它稳定地维持在冬季的几十亿分之0.25到夏季的几十亿分之0.65之间，有时会攀升至几十亿分之7。

That cyclical pattern has intrigued researchers back on Earth. Broadly speaking, there are two possible sources for Martian methane. 那种循环模式引起了地球上研究人员的兴趣。一般来说，火星甲烷有两种可能的来源。

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. 一种是太空，那里有富含碳的分子，其中一些可能分解成甲烷，抵达大小各异的流星上。

The other is from under the planet's surface. 另一种是来自行星表面之下。

Methane from both sources will mix eventually into the atmosphere. 两种来源的甲烷最终将混入大气中。

But if the gas is coming from underground, it will be more concentrated near its source, and might well appear on a seasonal basis. 但是如果气体来自于地下，那么它将更加集中于起源头附近，并且有可能表现出季节性。

The process could be a geological or geochemical one that is encouraged by the relative warmth of summer. That would be interesting. 这一过程可以是地质性或地球化学性的，并受到了夏季相对温暖气候的鼓动。这很有趣。

Or it could be biological, with methane-generating bugs waking up during the summer months. 或者它可以是生物学过程，产生甲烷的虫子在夏季的几个月中醒来。

That would be headline-grabbing. For either to be the explanation of the seasonality observed by Curiosity, 这将会成为新闻焦点。不论好奇号观测到的季节性解释是哪一种，

the rover would have to have had the luck to land in an area of such methane seeps. But such lucky breaks do happen. 探测车将有幸着陆在这片甲烷渗出的区域。但是这种幸运的事确实发生了。