第二篇 火星上有无生命
版本一：将火星上有不有生物的。前几段分析了一下火星的环境，大气啊，地上水流腐蚀的痕迹，火山什么的。还有问最后dry了的原因。最后说人类考察了火星上几个地方，那里土壤如何如何，稀薄大气无法阻挡太阳有害的射线，生物根本没法活。但是发现了一些化学成分，这些成分是生物必须的。。。
版本二：
火星表面有没有生命体。跟之前讲的差不多，手机快没电了，老师你看下自己总结的就知道了啦
版本三：
第一段说，如火星上有生命就怪了，因为条件太恶劣了。后面有拿地球与火星作对比，探究火星上有没有水这个事，有一个证据，多年前对火星上某个区域的照片，经研究那个区域曾经出现过水，因为有被侵蚀的痕迹还有河床神马的……
但是下面又有一个观点说，没有谁，是很久以前美国的宇航员登上去看的……
最后一段说，也许火星上有生命体可以存活的条件，但是现在绝对不行……
Atmosphere of Mars: Methane
Trace amounts of methane in the atmosphere of Mars were discovered in 2003 and verified in 2004.[ Mumma, M. J.; Novak, R. E.; DiSanti, M. A.; Bonev, B. P., "A Sensitive Search for Methane on Mars" (abstract only). American Astronomical Society, DPS meeting #35, #14.18.] [Michael J. Mumma. "Mars Methane Boosts Chances for Life". Skytonight.com. http://www-mgcm.arc.nasa.gov/MGCM.html. Retrieved February 23, 2007.] [ V. Formisano, S. Atreya T. Encrenaz, N. Ignatiev, M. Giuranna (2004). "Detection of Methane in the Atmosphere of Mars". Science 306 (5702): 1758–1761. Bibcode 2004Sci...306.1758F] [ V. A. Krasnopolskya, J. P. Maillard, T. C. Owen (2004). "Detection of methane in the martian atmosphere: evidence for life?". Icarus 172 (2): 537–547.]As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,[ Vladimir A. Krasnopolsky (February 2005). "Some problems related to the origin of methane on Mars". Icarus 180 (2): 359–367.] but asteroid impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as serpentinization are possible, the lack of current volcanism, hydrothermal activity or hotspots are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. However, research published in December 2009, ruled out this possibility.[ Court, R. and M. Sephton. 2009. Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere. Earth and Planetary Science Letters]
The existence of life in the form of microorganisms such as methanogens is among possible but as yet unproven sources. If microscopic Martian life is producing the methane, it likely resides far below the surface, where it is still warm enough for liquid water to exist.[ Steigerwald, Bill (January 15, 2009). "Martian Methane Reveals the Red Planet is not a Dead Planet". NASA's Goddard Space Flight Center (NASA). http://www.nasa.gov/mission_pages/mars/news/marsmethane.html. Retrieved January 24, 2009.]
Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and in vitro experiments testing growth of methanogenic bacteria on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% perchlorate salt.[ T. Goodhart, K.L. Howe and P. Gavin., T.A. Kral (2009). "CAN METHANOGENS GROW IN A PERCHLORATE ENVIRONMENT ON MARS?". 72nd Annual Meteoritical Society Meeting (2009). Lunar and Planetary Institute. http://www.lpi.usra.edu/meetings/metsoc2009/pdf/5136.pdf. Retrieved January 19, 2010.] The results reported indicate that the perchlorates discovered by the Phoenix Lander would not rule out the possible presence of methanogens on Mars.
A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.[ METHANE PRODUCTION BY METHANOGENS IN PERCHLORATE-SUPPLEMENTED MEDIA.". 40th Lunar and Planetary Science Conference (2009).]
BBC News: Ammonia on Mars could mean life[ http://news.bbc.co.uk/2/hi/science/nature/3896335.stm][ Written By Dr David Whitehouse]
Researchers say its spectral signature has been tentatively detected by sensors on board the European Space Agency's orbiting Mars Express craft.
Ammonia survives for only a short time in the Martian atmosphere so if it really does exist it must be getting constantly replenished.
There are two possible sources: either active volcanoes, none of which have been found yet on Mars, or microbes.
Suite of molecules
"Ammonia could be the key to finding life on Mars," one US space agency (Nasa) scientist told BBC News Online.
Spectral evidence for the gas was seen by the Planetary Fourier Spectrometer (PFS) on Mars Express.
Professor Vittorio Formisano, principal investigator for the instrument, is expected to release details of new findings from the PFS at an international conference being held next week in Paris.
The PFS is sensitive to radiation in the spectral region of 1.2-5 microns and 5-50 microns - a region rich with important molecules such as water and carbon dioxide. Ammonia has a spectral line at 10 microns.
Although Mars Express has been in orbit around Mars since December 2003, scientists have so far only analysed a fraction of the data the PFS has produced.
Researchers say this is because they are still coming to terms with the complexities of the PFS as well as coping with some nagging power problems on Mars Express.
So far the PFS has observed a depletion of carbon dioxide and an enrichment of water vapour over some of the large extinct volcanoes on Mars.
But it is the detection of minor compounds, possible in the sensors high-resolution mode, which are causing excitement.
The tentative detection of ammonia comes just a few months after methane was found in the Martian atmosphere. Methane is another gas with a possible biological origin.
Ammonia is not a stable molecule in the Martian atmosphere. If it was not replenished in some way, it would only last a few hours before it vanished.
One possibility the scientists have had to rule out is that the ammonia comes from the air bags of the failed Beagle 2 mission. Analysis has revealed that the suspected ammonia's distribution is not consistent with this explanation.
Life on Mars?
The importance of ammonia is that it is a compound of nitrogen and hydrogen.
Nitrogen is rare in the Martian environment but because no form of terrestrial life can exist without it, the presence of ammonia may indicate that Martian microbial life is hoarding it.
"There are no known ways for ammonia to be present in the Martian atmosphere that do not involve life," the Nasa scientist said.
The twin US rovers that landed on the Red Planet in January will be unable to answer the question of the ammonia's origin as they are designed for geological work.
But future missions could include sensors to analyse the ammonia to determine if it has a biological or volcanic origin. Lava deposited on to the surface, or released underground, could produce the gas.
But, so far, no active volcanic hotspots have been detected on the planet by the many spacecraft currently in orbit.