英语听力:自然百科 行星旅行指南:火星 Mars—17(在线收听

 It is chemically impossible for methane to survive for long in the Martian atmosphere, so it must have been released recently. 

 
Now what makes methane? Cows make methane? Probably not cows. Oh, microbes, various sorts can release methane, there are a variety of geographical processes, volcanoes can release methane, so the mere fact that there is methane doesn’t say life, but either way, the methane says that Mars is an active planet. It is either biologically active or it is geologically active or both. 
 
The methane release appears to be seasonal and links to areas of suspected subsurface ice, ice found exposed in fresh craters, has proven that water lurks not only near the poles but also much closer to the equator, it is pretty clear, that if the Viking Lander had dug just 4 inches deeper, they would have reached this ice and perhaps a totally different conclusion about life on the red planet. 
 
So if Mars has any life at all, whether it is so small you can only see with a microscope, or they had a mammoth, it wouldn’t matter to me, it’s the whole question of : is there life at all on Mars. 
 
Either way, there certainly will be life on Mars, the moment the first human traveler arrives. 
 
The fact that there are no scheduled flights to Mars hasn’t stopped people from preparing for the trip, and for a flight like this, planning is everything. And there we go. 
 
In 2009, 6 men walked into a series of connected rooms inside a warehouse in the Moscow suburbs and shut the door behind them for 3 months, they took all their food with them and drank recycled water, the only communication with the outside world was electronic, with a 20-minute/ delay. They were trying to simulate a flight to Mars.
  原文地址:http://www.tingroom.com/lesson/zrbaike/2012/260588.html