经济学人: 搜寻火星生命 (2)（打印版）

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. 不论它从何而来，根据地球的实验，火星大气中的任何甲烷分子将有望徘徊几个世纪。

It was to find signs of this more widespread material that a spectroscopic instrument called NOMAD (Nadir and Occultation for MArs Discovery), 正是为了发现更多关于这种普遍材料的迹象，一种搭载在ExoMars微量气体探测轨道飞行器上的

which is on board ExoMars Trace Gas Orbiter, was designed. And, as Ann Carine Vandaele of the Belgian Institute for Space Aeronomy told the AGU, 光谱仪器NOMAD被设计了出来。并且正如比利时航天航空研究所的安·卡林·凡达勒所告诉AGU的，

NOMAD has failed to find the slightest hint of methane in the Martian atmosphere. NOMAD并没有在火星大气中发现甲烷的任何最细微的线索。

Since NOMAD is 20 times more sensitive than the methane detector on board Curiosity, this is bad news. 由于NOMAD的敏感度是好奇号上所搭载的甲烷探测器得20多倍，因此这是个坏消息。

The findings are still under review, pending publication in a journal, and are therefore preliminary. 在结果发表于杂志期间，这些发现仍在审查之中，因此这些结果还在初级阶段。

But they do not surprise Kevin Zahnle of the Ames Research Centre, in California, a laboratory belonging to NASA, America's space agency. 但对于从属于美国太空署NASA的加利福尼亚艾姆斯研究中心的凯文·扎恩勒来说，这些结果并不惊讶。

Dr Zahnle has long argued that Curiosity's reports of Martian methane are artefacts. 扎恩勒博士长期以来都在争论称好奇号关于火星甲烷的报道是假象。

They are only marginally higher than control readings, 它们不过是在边缘函数上比控制读数稍高，

and those readings indicate the rover itself may be a source of methane (though nobody knows how), 并且那些读数表明探测车本身或许就是甲烷的一种来源（虽然没人知道其原理），

which further complicates taking accurate readings. 这进一步将获取正确读数复杂化。

The optimists will not be deflected, though. They note that NOMAD can probe only the upper part of Mars's atmosphere. 虽然乐观派不会因此停止脚步。他们注意到NOMAD仅能探测火星大气的上层部分。

Air with an altitude of less than 5km is beyond its range. 海拔不足5千米的大气不在其探测范围内。

Moreover, when ExoMars Trace Gas Orbiter flew over Gale, a dust storm obscured NOMAD's view of anything within 30km of the surface. 此外，当ExoMars微量气体探测轨道飞行器飞过盖尔山时，一场尘暴遮盖住了NOMAD 30千米范围内的视角。

Such optimists thus argue that the idea of methane seeping from the crater cannot be discounted. 因此这些乐观主义者争辩称甲烷从火山口喷射出的这种想法是没有市场的。

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. NOMAD似乎确实为我们展现了，如果甲烷存在于火星大气之中，那么它很稀少，并且限于大气的低层中。

But for now, neither side is willing to give way. 但目前，两边都不愿让步。

经济学人: 搜寻火星生命 (2)（在线收听）