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The discovery of life on Mars would excite just about everyone. But scientists looking for it would probably be happy, regardless of the outcome of their research – whether life is extinct, dormant or existing. They would even think that finding no evidence of life is an important discovery. But, as the saying goes, the lack of evidence is not evidence of the absence and it will take several decades of detailed exploration of Mars to be reasonably sure that the life has always been absent.
Mosaic of the hemisphere Valles Marineris of Mars projected in perspective, similar to what we would see of a spaceship. The distance is 2,500 km from the surface of the planet. The mosaic is composed of 102 images of Mars from Viking Orbiter. The center of the stage shows the entire system of Valles Marineris canyons, with a length of over 2,000 km and a maximum depth of 8 km, in the extension of Noctis Labyrinthus, the arched system from the graben to the west, up to the chaotic ground. to the east. Many old river canals run from the chaotic terrain of the north-central canyons to the north. The three Tharsis volcanoes (dark red spots), with a height of about 25 km each, are visible in the west. South of Valles, Marineris is a very old ground covered with many impact craters. Image credit: NASA / JPL-Caltech.
Until now, no direct observations of living organisms or fossils have been observed. But there are other types of evidence.
One of the most frequently cited cases is the controversial detection of methane in the planet's atmosphere, first in 2004 and again in 2014. This may have been produced by a past or present microbial life form. However, the abundance is so low that the data remains uncertain.
And in 2018, the team behind Trace Gas Orbiter of the European Space Agency said it had not discovered methane.
Now a new article, published in the journal Nature Geoscience, reports a new detection of methane in the atmosphere of the planet, as well as a theory on its origin. But given the difficulty of making reliable measurements of this gas, what confidence can we have in the results?
Double detection
The new research uses archival data acquired between 2012 and 2014 by the Fourier planetary spectrometer aboard Mars Express, which studies the composition of the planet's atmosphere through reflected and emitted infrared radiation from the planet. It is the same instrument that detected for the first time low concentrations of methane in the atmosphere of Mars in 2004.
The difference between the two sets of observations comes from the operating mode of the spectrometer. In 2004, the data was acquired by the instrument that traveled the atmosphere to the surface as Mars Express gravitated around the planet. In the new study, the instrument was pointed at a single surface and followed it while the spacecraft was in orbit.
The importance of the data stems from the characteristic that the team has chosen to follow: the crater Gale. This, of course, is the site where the Curiosity mobile is running – and where the onboard Curiosity tunable laser spectrometer has detected high levels of methane in 2014.
The Mars Express spectrometer tracked the Gale crater before, during, and after Curiosity detection. Interestingly, he has also detected high levels of methane in the region – a first simultaneous detection of methane on the surface and in the atmosphere. This may make the new measurement more reliable than previous detections.
The researchers also attempted to locate the source of methane using a grid mapping technique. They created computer models of emissions scenarios in each grid and also examined the geological features of each location to see if there were any potential sources of methane. They concluded that the methane had been released in an area east of Gale Crater and that the most likely source of the gas was a seepage of faults in the ice below the surface.
Finding where methane comes from is only one step in determining how it is formed. It is important to note that many mechanisms other than living organisms could have produced it, such as geological processes. For example, a geological event may have fractured ice containing methane bubbles to release it into the atmosphere.
But the new study does not attempt to draw conclusions about the origin of methane. However, the authors note that their results, particularly those that corroborate the Curiosity data, suggest that methane emissions are more likely to be due to small brief events rather than large episodic expirations. In fact, one might assume that smaller events are more likely than larger ones if Mars turns out to have experience of earthquakes (similar to an earthquake) that the Insight mission is programmed to detect.
So, whatever the source, it seems that there may be methane on Mars after all. However, we will need additional confirmation to be completely safe. Fortunately, new discoveries are likely to be available soon. The team that has failed to discover methane with Trace Gas Orbiter has been analyzing new data for several months.
As it has an extremely sensitive detector for on-board methane, it is expected that continuous data collection over the next few years will give a much better idea of the presence of seasonal or episodic methane variation atmospheric. Or it could reveal that it is only an illusionary wisp.
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Marco Giuranna et al. Independent confirmation of a peak of methane on Mars and a source area east of Gale Crater. Nature Geoscience, published online April 1, 2019; doi: 10.1038 / s41561-019-0331-9
Author: Monica Grady, Professor of Planetary and Spatial Sciences, The Open University.
This article was originally published on The conversation.
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