<P> 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 / CH ratios (less than approximately 40) indicate that life is likely present and active ." </P> <P> Sulfur dioxide in the atmosphere is thought to be a tracer of current volcanic activity . It has become especially interesting due to the long - standing controversy of methane on Mars . If methane on Mars were being produced by volcanoes (as it is in part on Earth) we would expect to find sulfur dioxide in large quantities . Several teams have searched for sulfur dioxide on Mars using the NASA Infrared Telescope Facility . No sulfur dioxide was detected in these studies, but they were able to place stringent upper limits on the atmospheric concentration of 0.2 ppb . In March 2013, a team led by scientists at NASA Goddard Space Flight Center reported a detection of SO in Rocknest soil samples analyzed by the Curiosity rover . </P> <P> As reported by the European Space Agency (ESA) on September 29, 2013, a new comparison of spacecraft data with computer models explains how global atmospheric circulation creates a layer of ozone (O 3) above Mars's southern pole in winter . Ozone was most likely difficult to detect on Mars because its concentration is typically 300 times lower than on Earth, although it varies greatly with location and time . The SPICAM--an UV / IR spectrometer--on board Mars Express has shown the presence of two distinct ozone layers at low - to - mid latitudes . These comprise a persistent, near - surface layer below an altitude of 30 km, a separate layer that is only present in northern spring and summer with an altitude varying from 30 to 60 km, and another separate layer that exists 40--60 km above the southern pole in winter, with no counterpart above the Mars's north pole . This third ozone layer shows an abrupt decrease in elevation between 75 and 50 degrees south . SPICAM detected a gradual increase in ozone concentration at 50 km until midwinter, after which it slowly decreased to very low concentrations, with no layer detectable above 35 km . The reporting scientists think that the observed polar ozone layers are the result of the same atmospheric circulation pattern that creates a distinct oxygen emission identified in the polar night and also present in Earth's atmosphere . This circulation takes the form of a huge Hadley cell in which warmer air rises and travels toward the south pole before cooling and sinking at higher latitudes . Mars is on a quite elliptical orbit and has a large axial tilt, which causes extreme seasonal variations in temperature amongst the northern and southern hemispheres . Mars's temperature difference greatly influences the amount of water vapor in the atmosphere, because warmer air can contain more moisture . This, in turn, affects the production of ozone - destroying hydrogen radicals . </P> <P> In early 2016, Stratospheric Observatory for Infrared Astronomy (SOFIA) detected atomic oxygen in the atmosphere of Mars . This was the first time in forty years it was detected, the last time being the Viking and Mariner missions in the 1970s . </P>

Mars atmosphere is 90 times the density of earths