Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.astrosociety.org/abh/pdf/ABH01transcript.pdf Дата изменения: Fri Jun 4 02:53:13 2010 Дата индексирования: Mon Oct 1 23:09:54 2012 Кодировка: Поисковые слова: mars polar lander

ASTRONOMY BEHI ND THE HEADLI NES A podcast for Infor mal Science Educator s from the Astr onomi cal Society of the Pacifi c www.astr osociety.or g/ abh Episode 1: ASTROBIOLOGY with guest Dr. Chris McKay fr om NASA Ames Research Center Written by Caroly n Collins Peters en Music by GEODESI UM Producer: Astronomic al Society of the Pacific Narrator: Welcome to Astronomy Behind the Headlines, a podcast from the Astronomic al Society of the Pacific. In this epis ode, we're going to talk about astrobiology and the searc h for life in the univ erse. Planet Earth has a complex web of lif e that manages to survive in some v ery interesting environments --plac es that we wouldn't ordinarily expect to be comfortable for living things ­ like hot springs, or near underwater volcanoes, or hidden beneath the Antarctic ice pack, or even inside rocks. Could life exist in those same kinds of places on other planets? When we look for signs of life on ot her worlds, what would we look for? How do we search it out ? And, how would we know if what we find is caused by living things -- or some other physical proc ess? These are all questions that the scienc e of astrobiology tries to ans wer. Astrobiology is the study of the origin, ev olution, and distribution of life in the univers e. It looks at where life IS, where it might have existed in the past, and where it could aris e in the fut ure. Astrobiology is an important tool in the search for life ­ and the conditions that support it ­ not just in our own solar system, but also on planets around other stars.
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In our own solar system, Mars is one of the most obvious places where astrobiologists searc h for life. Starting wit h the Viking landers in t he 1970s, through the more recent rovers, landers, and mapper missions, scientists have been studying the Mars environment to find out whether it could support liv ing things -- or if it ever has. The res ult is a good news/bad news scenario. The good news is that Mars has had water in the past. In fact, it has water now, although mostly in froz en form. The bad news is that, so far as we know right now, there is no ev idence that lif e exists on Mars. We've found no fossils of ancient Mars life yet, and if it did exist, it may have been limited to microbes. So, the search for past Mars inhabitants could well be a searc h for the remains of very tiny organis ms. What would those remains look like? We asked Dr. Chris Mc Kay, a planetary scientist at the NASA Ames Res earch Center in Calif ornia. Chris, what are we s earc hing for on Mars that would tell us if life ev er existed there -- or if it exists now? CHRI S McKay: Well, the evidence that's interesting about Mars is that it had wat er early in its history, and that's what mak es us optimistic that it may hav e had a separate origin of life -- separate and independent of Eart h life. To my mind, that's what we're looking for on Mars. We're looking for a second genesis. And what this means that it is not enough to just find life on Mars. We hav e to show that that the lif e that we find there is different from Earth lif e. And, showing this is n't easy. Fossils, which is what people often talk about as a target for a searc h for life on Mars can't be used to determine if Martian life was the same as Earth life. A fossil is just a form of life, it's not an actual organis m. To demonstrate that life on Mars is different from life on Earth requires that we actually have the biological remains of a Martian organis m . I think the best plac e to search for such remains is in the ancient frozen terrain near the polar caps. So, an analogy is frozen mammoths in Siberia on Eart h, where we find ancient,organis ms -- in this case, mammoths -- frozen in the ic e. The same idea on Mars -- just much, muc h older and much, muc h s maller.
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Narrator: Based on our experience in the search f or life on Mars, what can we carry forward as we look for habitable planets and life elsewhere? CHRI S: Well, looking at the Earth and looking at Mars, we realiz e that liquid water is the key environmental requirement for life. And, henc e the notion of "follow the wat er." So, when we look at planets around other stars we're interest ed in is planets with surf ace temperatures in the range to allow liquid water. But, there's another point that we learn by comparing Earth and Mars I think that's equally important. And that is that Earth kept its water and Mars did not. The differenc e is due to size. Earth is almost 10 times bigger than Mars, more massive -- and yes, folks, size matters. This means that when we look at other planets we want to determine not just that their surfac e temperatures are suitable for liquid water, but also that their size is suitable to maintain the s ort of activities -- plate tectonics, volcanis m, and magnetic fields -- that maintain the habitability of the planet . And, we think a planet must be at least half the size of earth to keep its liquid water over geological time. Mars is too s mall, Earth's fine, somet hing may be half the siz e of the Earth would be all right. Narrator: Astronomers have been finding planets around other stars since the late 20th century. Ev entually, they 'll develop tools to det ect the presence of life on thes e exoplanets -- if it exists. Today, the Kepler mission is searching for Eart h-like planets that liv e in the habitable zones near their stars. These worlds could well have environments wit h liquid water, where life might possibly ex ist. They will help astrobiologists underst and the many factors that influenc e the origin and evolution of life, and where it can survive and flouris h. You'll find more information about astrobiology and the search for life on other worlds at the Astronomical Society of the Pacific's Astronomy from the Ground Up webs ite. Surf on ov er to www.astros ociety.org/abh. Thanks for listening!

Astronomy Beh ind the Headlines Episode 1: ASTROBIOLOGY

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