文章大意:本文是一篇说明文。美国国家航空航天局禁止航天器访问火星上可能存在液态水,即生命可能繁衍的地方,以免地球微生物污染火星。但新的研究表明火星上液态水太咸、太冷,人类所知道的生命不可能在火星表面生存下来。我们应该解除禁令,访问这些特殊区域,帮人类解开火星谜题。
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 to polluting Mars with Earth microbes (微生物) . 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 Institute in 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 salty water on the surface of Mars up to 18 per cent of the year, depending on the season, no microbe we have even seen on Earth would be able to reproduce there.
“Life as we know it is not going to find the brines (盐水) 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 pollute 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 such as Curiosity to pollute Mars.
“The levels of sterilisation (杀毒) 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.
43. 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 polluting Mars |
D.human beings know nothing about these areas and they are dangerous to us |
44. 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 pollute Mars because the surface of the planet is either too cold or too salty |
C.The fear of polluting Mars is unnecessary because human beings have no intention of that under any circumstances |
D.Jennifer Hanley thinks human beings should explore the special regions on Mars in order to prove the existence of Martian life. |
45. 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. |
46. Which might be the best title for the passage?
A.Water on Mars too Salty for Earth Life | B.Curiosity rover; The ultimate guide |
C.Mysteries of Mars to be Unveiled | D.The Salty Water of Life |