VOA科学技术2024--Why Is Methane Gas Coming Out of the Ground on Mars?

Scientists are seeking to find out what is producing the slow release of methane¹ gas on Mars.

Methane often results from biological processes. On Earth, most of the gas comes from living creatures. For this reason, the American space agency NASA has been investigating methane levels on Mars in a search for signs of current or past life. So far, no evidence has been found.

But a new study is providing fresh details about methane on Mars. NASA's Curiosity explorer, or rover, has repeatedly measured methane levels on the Martian surface. The rover arrived on Mars in 2012 and has been exploring areas around Gale² Crater³. This area is believed to have contained a lake at one time and has also shown other evidence of flowing water in the past.

NASA says Gale Crater is the only place where methane has been discovered. Even a spacecraft sent to collect data on the Martian atmosphere has not identified the presence of methane. That spacecraft, the ExoMars Trace Gas Orbiter, is operated by the European Space Agency.

In addition to only being discovered, or detected, around Gale Crater, the observations of methane happen only at night, NASA researchers recently reported. Levels also go up and down during different seasons and at times, rise sharply for short periods.

The mysterious methane releases leave scientists considering "a lot of plot twists," said Curiosity project leader Ashwin Vasavada. But a NASA research group recently proposed a possible explanation for how the gas behaves on Mars.

The researchers theorize that all detected methane could be trapped, or sealed, underneath⁴ hardened pieces of salt in Martian regolith. Regolith describes soil that contains rock and dust that sits on or below the surface.

The scientists say increases in temperature might explain the differences in gas release. During certain seasons or times of day warmer temperatures could weaken the seal on the methane, causing gas to be released.

NASA said the research was led by Alexander Pavlov, a planetary scientist at the agency's Goddard Space Flight Center in Maryland. He said small amounts of methane could also be released when the regolith seal is broken by weight from above, for example, when the Curiosity rover drives over the area.

Pavlov said this theory could help explain why methane levels have only been discovered in the Gale Crater area. It is the only place on Mars where NASA's Curiosity rover is currently active.

NASA has another rover working on Mars, Perseverance⁵. But it has been exploring the Jezero Crater area on another part of the planet. Jezero Crater is also believed to have contained large water bodies in the distant past. But Perseverance is not equipped with a methane-detecting instrument.

Pavlov noted⁶ that the latest theory came from his memories of an unrelated experiment carried out in 2017. The experiment involved growing microorganisms in a simulated Martian environment that included frozen soil that contained salt.

During that experiment, researchers observed that the collection of soil on top formed an icy, salty crust. Changes in conditions caused the ice to melt, turning the solid material into a gas and leaving the salt behind.

Pavlov's team tested five samples of frozen soil containing different kinds of salt material commonly found on Mars. A new set of Earth-based experiments was carried out in which the frozen material was exposed to different temperatures and air pressures inside an environment at Goddard that was designed to be like Mars.

The team was able to repeatedly copy the salt sealing process in Mars-like conditions during laboratory testing. The researchers said they plan to keep carrying out experiments under different conditions and using salt minerals to confirm their theory.

But the researchers noted that to carry out more detailed⁷ methane investigations⁸, they will likely need a whole new generation of sensitive instruments. These would be designed to measure methane continuously from many places on Mars.

Words in This Story

plot twist - n. an unexpected development that happens in a play, movie, etc.

simulate - v. to do or make something that behaves or looks like something real, but which is not

crust - n. the hard, dry layer on the surface of something

expose - v. to remove what is covering something so that it can be seen

1 methane   

n.甲烷，沼气

参考例句：

• The blast was caused by pockets of methane gas that ignited.爆炸是由数袋甲烷气体着火引起的。
• Methane may have extraterrestrial significance.甲烷具有星际意义。

2 gale   

n.大风，强风，一阵闹声（尤指笑声等）

参考例句：

• We got our roof blown off in the gale last night.昨夜的大风把我们的房顶给掀掉了。
• According to the weather forecast,there will be a gale tomorrow.据气象台预报，明天有大风。

3 crater   

n.火山口，弹坑

参考例句：

• With a telescope you can see the huge crater of Ve-suvius.用望远镜你能看到巨大的维苏威火山口。
• They came to the lip of a dead crater.他们来到了一个死火山口。

4 underneath   

adj.在...下面，在...底下；adv.在下面

参考例句：

• Working underneath the car is always a messy job.在汽车底下工作是件脏活。
• She wore a coat with a dress underneath.她穿着一件大衣，里面套着一条连衣裙。

5 perseverance   

n.坚持不懈，不屈不挠

参考例句：

• It may take some perseverance to find the right people.要找到合适的人也许需要有点锲而不舍的精神。
• Perseverance leads to success.有恒心就能胜利。

6 noted   

adj.著名的，知名的

参考例句：

• The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
• Jim is noted for arriving late for work.吉姆上班迟到出了名。

7 detailed   

adj.详细的，详尽的，极注意细节的，完全的

参考例句：

• He had made a detailed study of the terrain.他对地形作了缜密的研究。
• A detailed list of our publications is available on request.我们的出版物有一份详细的目录备索。

8 investigations   

（正式的）调查( investigation的名词复数 )； 侦查； 科学研究； 学术研究

参考例句：

• His investigations were intensive and thorough but revealed nothing. 他进行了深入彻底的调查，但没有发现什么。
• He often sent them out to make investigations. 他常常派他们出去作调查。