Question

    There are certain areas on Mars where we don’t dare tread. NASA forbids spacecraft from visiting spots that possibly host liquid water, and so where life might be able to thrive, for fear of contaminating (感染) Mars with Earth microbes. But an analysis of the salty liquids on Mars suggests we needn’t worry, because life as we know it should be unable to exist anywhere on the planet’s surface.

Edgard Rivera-Valentin at the Lunar and Planetary Institutein Texas and his colleagues used readings of the temperature and relative humidity across Mars to map the presence of salty water. Any water on the surface is likely to be salty, simply because the surface is. This boosts the chances of water being liquid because salt lowers its freezing point.

It is like when you throw salt on an icy sidewalk, says Danielle Nuding at NASA’s Jet Propulsion Laboratory in California. “It’s the same chemistry happening.”

Unfortunately, the saltier the water, the less likely anything can survive in it. The team found that even though there could be briny (盐分多的) water on the surface of Mars up to 18 per cent of the year, depending on the season, no microbe we have ever seen on Earth would be able to reproduce there.

Life as we know it is not going to find these brines and survive because it’s either going to be way too cold or way too salty,” says Rivera-Valentin, who presented the results at the Lunar and Planetary Science Conference in Texas.

That doesn’t mean we can’t contaminate Mars: brines with different types of salts mixed together might be friendlier to life and temperatures just below the surface are much less extreme. Nevertheless, as long as we don’t dig down, it might be highly unlikely or even impossible for rovers (飞行器) such as Curiosity to contaminate Mars.

“The level of sterilization (杀菌) that we’ve done with Curiosity should be good enough to ignore the ban on visiting what we’ve been calling special regions until now, says Jennifer Hanley at Lowell Observatory in Arizona. I think that we’re OK to go. Visiting these regions would be particularly helpful because, while they are in theory the most vulnerable areas on Mars, they are also the most interesting.

For example, arguments have been raging for over a decade about whether dark streaks on Martian slopes called recurring slope lineae are flowing water or just dust. A quick visit by Curiosity, which is near an area where the flows often form, could solve it once and for all.

Even if areas with water are inhospitable to Earth life, they could still be home to native Martian life forms.

“If you had life that originated on Mars when it was more habitable, it could be that as Mars changed, life could have gradually adapted to the new, more extreme conditions,” says Rivera-Valentin.

1.NASA forbids spacecraft from visiting the special regions on Mars because            .

A.life is unable to thrive there, thus there’s no point of visiting them

B.Martian life probably exists there and might threaten human beings

C.they worry Earth microbes might survive there, thus contaminating Mars

D.human beings know nothing about these areas and they are dangerous to us

2.Which of the following statements is true?

A.Mars surface being salty provides evidence that Mars hosts liquid water.

B.Earth life is unlikely to contaminate Mars because the surface of the planet is either too cold or too salty.

C.The fear of contaminating Mars is unnecessary because human beings won’t contaminate Mars under any circumstances.

D.Jennifer Hanley thinks human beings should explore the special regions on Mars in order to confirm the existence of Martian life.

3.What is the point of visiting the special regions on Mars?

A.Martian life might be found.

B.Liquid water might be found.

C.Many puzzles about Mars could soon be solved.

D.No humans have ever visited those regions before.

4.In the passage, you can find the answers to all the questions except            .

A.whether the surface of Mars is salty or not

B.whether any native Martian life forms exist

C.whether Earth life is able to survive on Mars or not

D.whether the rover Curiosity will contaminate Mars

Answer

1.C

2.B

3.C

4.B

【解析】

这是一篇说明文。文章介绍了在火星上人类不敢去涉足的地方实际上是探索起来对人们有很多帮助的地方。美国国家航空航天局禁止航天器访问可能存在液态水、生命可能繁衍的地方，以免地球微生物污染火星。但实际上对火星上含盐液体的分析表明，人类所知道的生命应该不可能存在于火星表面的任何地方。访问火星上一些有禁令的地区将特别有帮助，因为虽然它们理论上是火星上最脆弱的地区，但可以帮人类解开谜题。

1.细节理解题。根据第一段中的NASA forbids spacecraft from visiting spots that possibly host liquid water, and so where life might be able to thrive, for fear of contaminating Mars with Earth microbes.(由于担心地球上的微生物污染火星，美国宇航局禁止宇宙飞船前往可能存在液态水的地方，因为那里可能有生命存在)可知，美国宇航局禁止宇宙飞船访问火星上的特殊区域，是因为担心地球微生物污染火星。故选C项。

2.细节理解题。根据第五段中的Life as we know it is not going to find these brines and survive because it’s either going to be way too cold or way too salty(我们所知道的生命不会找到这些盐水并存活下来，因为它要么太冷，要么太咸)可知，地球微生物不可能污染火星，因为火星表面要么太冷，要么太咸。因此B项说法正确。故选B项。

3.推理判断题。根据倒数第三段中的A quick visit by Curiosity, which is near an area where the flows often form, could solve it once and for all.(好奇号在一个经常形成水流的区域附近快速访问，可以一劳永逸地解决这个问题)可推知，访问火星上那些特殊区域可以帮助人们解决许多火星之谜。故选C项。

4.细节理解题。题目问以下哪个选项不能从文中找出答案，此题可用排除法。根据第二段中的“Any water on the surface is likely to be salty, simply because the surface is.”得知火星表面是否是咸的，故排除A项；根据第五段中的“Life as we know it is not going to find these brines and survive because it’s either going to be way too cold or way too salty”可知，地球生物不能在火星上生存，故排除C项；根据第六段最后一句“Nevertheless, as long as we don’t dig down, it might be highly unlikely or even impossible for rovers such as Curiosity to contaminate Mars.”可知，好奇号不会对火星造成污染，故排除D项。文章中没有提及“火星上是否有生命存在”，所以这个描述是无法判断的。故选B项。