[DOC] [TLE] CSI: AliensAstronomers Prep to Detect Cryptic Exoplanet Biosignals [PAR] May 12, 2015 ... Investigators eager to learn whether any exoplanets harbor life ... This spectrum 
can reveal the chemicals in the exoplanet's atmosphere and, sometimes, on its 
surface. Earth, for example, would look green from all the photosynthesizing ... 
gas might obscure smaller amounts of other gases being created. [DOC] [TLE] Alien Atmospheres - Methane, CFCs and Signs of Extraterrestrial ... [PAR] Jul 25, 2014 ... How the search for industrial pollutants could narrow the search for alien ... is an 
excellent candidate as a first clue that life exists on other planets. On Earth, and 
perhaps elsewhere in the Universe, methane (CH4) is both a ... gases in the 
atmosphere, or failing to, would help us discern if life was likely there. [DOC] [TLE] Alien Atmospheres: The Search for Signs of Life - Space.com [PAR] Jan 5, 2016 ... Hunting for signs of alien life means knowing just what living things do to their ... 
Astronomers have discovered nearly 2,000 exoplanets to date. ... radon  life 
produces every gas available in Earth's atmosphere, she added. [DOC] [TLE] When Will Mankind Achieve First Contact with Extraterrestrial Life ... [PAR] advanced intelligent life forms that exist in our solar system, we must look ... and 
increasingly polluted atmosphere is the astronomer's single greatest impedi- ..... 
For example, specific chemicals or gases which, on Earth, are detectable in 
either ..... the matter is converted to a very large amount of energy (it is this 
energy from. [DOC] [TLE] Atmosphere of Mars - Wikipedia [PAR] The atmosphere of Mars is the layer of gases surrounding Mars. It is composed 
mostly of ... Mars's atmospheric mass of 25 teratonnes compares to Earth's 5148 
... before the lakebed in the crater was formed; afterwards, large amounts of .... In 
2011, NASA scientists reported a comprehensive search using ..... Astronomy... [DOC] [TLE] Oxygen is not definitive evidence of life on habitable extrasolar planets [PAR] Sep 10, 2015 ... The Earth's atmosphere contains oxygen because plants continuously ... can 
supply significant amount of abiotic oxygen on habitable more ... of science to 
promote astrobiology in the search for life on extrasolar planets. ... 17 million 
miles away are giving astronomers fresh clues to how that gas might... [DOC] [TLE] Unit 1 : Many Planets, One Earth - Annenberg Learner [PAR] Astronomers have discovered dozens of planets orbiting ... Next we briefly survey 
the evolution of life on Earth from simple life forms through ... Instead they contain 
large amounts of iron, silicates (silicon and oxygen), ... As we will see in Unit 2, "
Atmosphere," CO2 is a greenhouse gas that traps heat ...... Methane (CH4). [DOC] [TLE] Institute for Planets and Life - STScI [PAR] Europa is one of the most enticing targets in the search for life beyond Earth. ... 
electron donors and acceptors in hydrothermal systems (e.g. H2 + CH4 and CO2) 
that .... especially Super-Earths with atmospheres that retain substantial amounts 
of .... composition, formation, and habitability of these alien worlds is still sketchy. [DOC] [TLE] 2009 May Symposium Talks - STScI [PAR] Hydrothermal systems produce volatiles, such as H2, H2S, CH4, CO, CO, and 
trace ... provide clues about the kinds of reactions that initiated the chemistry of 
life. ... Yet, as we learned from the Viking and Phoenix missions, the search for 
life signs ... Tools used routinely to detect life on Earth are not likely to detect 
alien life. [DOC] [TLE] The Colors of Exobiology - Centauri Dreams [PAR] Jun 22, 2007 ... The most obvious signature for life itself is the presence of unusual ... examples 
of extrasolar planetary spectra from terrestrial-class worlds to look at. ... in higher 
concentrations of biogenic gases CH4, N2O, and CH3Cl. .... They concluded that 
the large amount of O2 and the simultaneous presence of CH4... [DOC] [TLE] More Details from Hubble Reveal Strange Exoplanet is a Steamy ... [PAR] GJ1214b, shown in this artist's view, is a super-Earth orbiting a red dwarf star 40 
... light is filtered through the planet's

Question: A clue for alien astronomers looking for life on Earth is the large amount of this gas, CH4, in the atmosphere
Answer: methane