科學(xué)60秒:火星的大氣層哪兒去了？
來源：滬江聽寫酷
2011-05-25 00:02
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The clues are adding up to give a picture of a distant Martian past, when the planet had a thick atmosphere that was warm enough for water to stream on the surface. But now the water’s gone, and the atmosphere is so thin that any water would ____1____.
In fact, the vestigial atmosphere is still slowly dissipating into space. Why? Well, researchers believe that solar wind and radiation is ____2____, and they’re planning a mission to find out, called MAVEN: Mars Atmosphere and Volatile Evolution Mission.
The solar wind is a stream of electrically-charged particles. ____3____. We on Earth have protection in the form of a magnetic shield. But that shield is dead on Mars, gone for billions of years.
Instead, the solar wind and the sun’s UV radiation give an electric charge to atoms and particles in Mars outer atmosphere. Then electric fields generated by the solar wind ____4____ the charged particles. So the atmosphere becomes even thinner.
Maven is scheduled to reach the red planet in 2014. Which will allow researchers to measure how much water and atmosphere are ____5____.
The clues are adding up to give a picture of a distant Martian past, when the planet had a thick atmosphere that was warm enough for water to stream on the surface. But now the water’s gone, and the atmosphere is so thin that any water would ____1____.
In fact, the vestigial atmosphere is still slowly dissipating into space. Why? Well, researchers believe that solar wind and radiation is ____2____, and they’re planning a mission to find out, called MAVEN: Mars Atmosphere and Volatile Evolution Mission.
The solar wind is a stream of electrically-charged particles. ____3____. We on Earth have protection in the form of a magnetic shield. But that shield is dead on Mars, gone for billions of years.
Instead, the solar wind and the sun’s UV radiation give an electric charge to atoms and particles in Mars outer atmosphere. Then electric fields generated by the solar wind ____4____ the charged particles. So the atmosphere becomes even thinner.
Maven is scheduled to reach the red planet in 2014. Which will allow researchers to measure how much water and atmosphere are ____5____.
boil away
behind the theft
It continuously flows from the sun out into space
sweep away
gone with the solar wind
諸多線索綜合起來為我們描繪出一幅畫面：那是火星遙遠(yuǎn)的過去，那時的火星還有著一層厚厚的大氣層，令這顆星球溫?zé)崤?，從而使水能夠在火星表面流淌。但如今，地表的水消失不見，而大氣層變得如此之薄，任何水分都會蒸發(fā)掉。
事實(shí)上，殘余的大氣層仍在緩慢地消散于太空中。為什么呢？唔，研究人員認(rèn)為太陽風(fēng)和輻射是“幕后黑手”，他們打算開展一項(xiàng)任務(wù)來找出原因何在。這項(xiàng)任務(wù)名為MAVEN——火星大氣與揮發(fā)物演化任務(wù)（Mars Atmosphere and Volatile Evolution Mission）。
太陽風(fēng)是一股帶點(diǎn)粒子流。它由太陽不斷發(fā)出，流入太空中。我們在地球上受到磁場屏蔽的保護(hù)，而火星的電磁場早在億萬年前就已經(jīng)消失了。
這樣，太陽風(fēng)和太陽的紫外輻射賦予火星外層大氣中的原子和粒子一個電荷，然后由太陽風(fēng)產(chǎn)生的電場將帶電粒子一掃而空。因此，火星的大氣層變得越來越薄。
預(yù)計(jì)Maven將于2014年抵達(dá)這顆紅色星球。屆時，研究人員將能測出究竟有多少水和大氣隨太陽風(fēng)而逝。