国家地理:Is It Real? Life on Mars 火星生命（在线收听） |
| Believe it or not, astrobiologist Penny Boston is searching for life on Mars by dropping deep into this heart of darkness. This is a lava tube, a subterranean cave formed by underground lava flows during volcanic eruptions that occurred thousands of years ago. And Boston has someone she wants us to meet. Sometimes they are in crevices. Sometimes they are kinda hard to see. Is this one, the scary monster reveals itself? Ah! There is one. Actually no. This is an extremophile. We are looking for what we astrobiologyists call extremophiles in this environment. That means that they are organisms that are living in very difficult conditions. In this particular case, these organisms are living in a very cold cave right around freezing. They are making their living without benefit of sunlight and there is almost nothing to eat in this cave. In recent years, scientists have discovered tenacious microorganisms living in all forms of extreme environments. So if on Earth, why not on Mars? We think that Mars is covered with lava tubes. We believe that by looking at organisms that live in these extreme circumstances on Earth, we can learn a lot about what to look for on Mars; and that, similar Martian organisms may be able to persist on Mars in places very similar to this lava tube. To find out, Dr. Boston has created her own little Mars environment biospheres, essentially exposing a range of microscopic Earth life forms to various elements to be expected on Mars. They have been subjected to Mars-like levels of high ultraviolet radiation, and Mars-like temperature cycles. We have given them atmosphere compositions from very low levels of carbon dioxide with nothing else to, perhaps, 1/10 the density of Earth's atmosphere, and tested them under those conditions. And so far, she's isolated 36 different strains of organism that thrive quite happily. So in theory at least, life could survive the harsh conditions of Mars except for one problem. There is one thing for sure that we know, and that is that all forms of life on our planet require liquid water. We don't know if that's going to be true on other planets. But we think that where there is going to be life, there is going to have to be water. astrobiologist: one who specializes in astrobiology, one who studies life on celestial subterranean: existing, occurring, or done under the earth's surface extremophile: microorganism that lives in extreme environmental conditions tenacious: persisting in existence |
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