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  3. Time was when the solar system had two watery worlds. (46)Directly next door to the warm. wet, loamy Earth was the warm, wet, lo

Time was when the solar system had two watery worlds. (46)Directly next door to the warm. wet, loamy Earth was the warm, wet, lo

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问题     Time was when the solar system had two watery worlds. (46)Directly next door to the warm. wet, loamy Earth was the warm, wet, loamy Mars, both planets covered with oceans and running with rivers-and both possibly teeming with life. Billions of years ago, however, the low-gravity Mars had both its air and water leak away, causing the planet to become the dead, freeze-dried place it is today.
    That is what the prevailing thinking has been. Now, it appears that thinking may be wrong. (47)Recently, NASA released new images from the Mars Global Surveyor spacecraft that suggest water may be flowing up and streaming onto the Martian surface-dramatically increasing the likelihood that at least part of the planet is biologically alive. "If these results prove true," says Ed Weiler, associate administrator of NASA’s Office of Space Science, "they have profound implications for the possibility of life."
    Finding liquid water on Mars’ surface has never been easy-because it simply can’t exist there. The modern-day Martian atmosphere has barely 1 percent the density of Earth’s, and its average temperature hovers around-67 degrees Fahrenheit (-19 degrees Centigrade). In an environment as harsh as this, water would either vaporize into space or simply flash-freeze in place. (48)Scientists studying Martian history have always looked for clues the planet’s ancient water left behind-tracks where vanished rivers once flowed, basins where vanished seas once stood.
    (49)The approximately 65,000 images the Surveyor orbiter has beamed home in the nearly three years it has been circling Mars are full of this kind of expected hydro-scarring. But some of the pictures took scientists by surprise. The older a formation is, the more likely it is to have been distorted over the eons-smoothed by periodic windstorms or gouged by the occasional incoming meteor. However, a few of the newly discovered water channels look fresh. That discovery has lead astonished researchers to conclude that these channels may have been recently formed.
    (50)Planetologists have long assumed that if underground water was going to bubble up on Mars, it would have to be somewhere in the balmy equatorial zones: where temperatures at noon in midsummer may reach 68 degrees Fahrenheit (20 degrees Centigrade). Almost all the new channels, however, were discovered at the planet’s relative extremes-north of 30 degrees north latitude and south of 30 degrees south latitude-and all were carved on the cold, shaded sides of slopes.

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答案研究火星史的科学家们一直在寻找这个星球上古远的水曾经留下的线索—消失的河流曾经流淌过的印迹，或者是消逝的海洋曾经覆盖的盆地。
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