Time was when the solar system had two watery worlds. 46){{U}} 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{{/U}}. 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){{U}} 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. {{/U}}"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){{U}} 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.{{/U}}
49) {{U}}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{{/U}}. 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){{U}} 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){{/U}}. 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.