VOA标准英语10月-Snow Falling From Martian Atmosphere（在线收听）

Soil sample taken from informally named 'Snow White' trench at NASA's Phoenix Mars Lander work site produced minerals that indicate evidence of past interaction between the minerals and liquid water

Icy snow falls through the atmosphere of Mars. That finding was beamed back to Earth by the space probe Phoenix, which has been continuously monitoring the weather on the red planet since it landed four months ago.

Jim Whiteway is lead scientist for NASA's Phoenix meteorologist mission. "The ice crystals would be starting out at about a height of about four kilometers. And by the end of the measurement, in this case, they have fallen all the way down to about to 2.5 kilometers," he said. "So that is snow is falling from the clouds and we are going to be watching very closely over the next month for evidence that snow is actually landing on the surface."

Snow, which began falling about a month ago, is not the only surprising finding announced this week by managers of NASA's Phoenix mission.

The space probe discovered materials in the Martian soil that can only be produced through the interaction with water. These include a silicate mineral and calcium carbonate, according to senior project scientist William Boynton.

"Carbonates are very common minerals on Earth," he said. "They commonly form by the interaction of liquid water with carbon dioxide gas. And that is just what we think is going on in the surface of Mars. Another form in which people are familiar is just common chalk that you use for writing on black boards."

The Phoenix mission was undertaken because scientists believed there was ice just below the surface of the northern planes of Mars, something that was confirmed by the space probe shortly after it landed.

NASA principal investigator Peter Smith says the evidence points more and more to the conclusion that there was once life on Mars.

Smith notes that Mars was probably a much warmer planet millions of years ago because an unstable spin placed Mars' northern pole more directly toward the Sun. A warmer climate suggests the presence of liquid water and the existence of life, according to Smith.

"Is this a habitable zone on Mars? Well, I think we are approaching that hypothesis," he said. "We understand though that Mars has many surprises for us and we have not finished our investigation and so it is too soon to be sure of this, but we are certainly finding a lot of the indicators that we proposed to find at the beginning of this mission."

With the approaching winter and freezing temperatures, Phoenix is not expected to continue its research mission for many more weeks to learn, among other things, whether snow crystals reach the ground. But NASA investigators hope to jump start the space probe once Martian daylight returns.