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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 1.0 wt% perchlorate
salt. The results reported indicate that the perchlorates discovered by the Phoenix
lander would not rule out the possible presence of methanogens on Mars.
It was suggested that both phenomena - methane production and degradation -
could be accounted for by ecology of methane-producing and methane-consuming
microorganisms.
In June 2012, scientists reported that measuring the ratio of hydrogen and
methane levels on Mars may help determine the likelihood of life on Mars.
According to the scientists, low H
2
/CH
4
ratios (less than approximately 40) indicate
that life is likely present and active (Oze et al.
2012
). Other scientists have
recently reported methods of detecting hydrogen and methane in extraterrestrial
atmospheres.
In contrast to the findings described above, studies by Kevin Zahnle, a planetary
scientist at NASA's Ames Research Center, and two colleagues conclude that there
is as yet no compelling evidence for methane on Mars. They argue that the strongest
reported observations of the gas to date have been taken at frequencies where
interference from methane in Earth's atmosphere is particularly difficult to remove
and are thus unreliable. Additionally, they claim that the published observations
most favorable to interpretation as indicative of Martian methane are also consistent
with no methane being present on Mars (Zahnle et al.
2011
).
The Curiosity rover, which landed on Mars in August 2012, is able to make
measurements that distinguish between different isotopologues of methane; but even
if the mission is to determine that microscopic Martian life is the seasonal source
of the methane, the life forms probably reside far below the surface, outside the
rover's reach. The first measurements with the tunable laser spectrometer (TLS) in
the Curiosity rover indicated that there is less than 5 ppb of methane at the landing
site at the point of the measurement. On July 19, 2013, NASA scientists published
the results of a new analysis of the atmosphere of Mars, reporting a lack of methane
around the landing site of the Curiosity rover. On September 19, 2013, NASA again
reported no detection of atmospheric methane with a measured value of 0.18
˙
0.67
ppbv corresponding to an upper limit of only 1.3 ppbv (95 % confidence limit) and,
as a result, concluded that the probability of current methanogen microbial activity
on Mars is reduced.
India's Mars Orbiter Mission, launched on November 5, 2013, will search for
methane in the atmosphere of Mars using its Methane Sensor for Mars (MSM).
The orbiter is scheduled to arrive at Mars on September 24, 2014. The Mars Trace
Gas Mission orbiter planned to launch in 2016 would further study the methane, if
present, as well as its decomposition products such as formaldehyde and methanol.
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