A publication in Icarus

MAVEN confirms rapid erosion of Mars atmosphere


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Artist’s rendition of a solar storm hitting Mars and stripping ions from the upper atmosphere.Credit: NASA/GSFC

After 4 years orbiting Mars, the MAVEN probe was able to collect many data. An international scientific team - including Arnaud Stiepen of the Laboratory of Atmospheric and Planetary Physics (LPAP) of the STAR Research Unit - has just analyzed the latest information transmitted by the probe which reveals a very rapid erosion of the Martian atmosphere. These results are the subject of a scientific publication in the journal Icarus (1).

T

he Mars Atmosphere and Volatile EvolutioN (MAVEN) probe, launched by NASA in 2013, has been placed in orbit around Mars to collect data enabling scientists to understand how the Sun was able to strip most of its atmosphere from it, transforming this once potentially habitable planet into a cold and dry desert world. First space mission dedicated to exploring the upper atmosphere of Mars, MAVEN has come to the end of the mission for which it was designed. The data collected by the American probe allow us today to draw the evolution of the atmosphere and climate of Mars, but also its habitability. « The published results are very important because they come from all the instruments on board, says Arnaud Stiepen, researcher at LPAP - STAR Institute and co-author of the publication. And these have clearly determined the rate of escapement from the atmosphere of Mars. »

MAVEN Mars vs Earth Solar Wind (c)NASA

The solar wind interacts with the Mars upper atmosphere, but is deflected past Earth by a global magnetic field (artist's concept). Credit: NASA/GSFC

If the red planet once had (in geological time) a dense atmosphere, potentially favourable to the development of life, today it has become rather tenuous, if not almost non-existent in certain places. Mars no longer has a global magnetic field to protect it from the Sun's attacks, so it is constantly bombarded and its atmosphere is eroding rapidly. We knew this phenomenon existed but we had not yet been able to quantify it. The MAVEN mission analyzed the planet from every angle as the probe "looked at" it for a full Martian year - about 687 Earth days - mapping almost 100% of its surface. « Not only have we been able to quantify the erosion of the atmosphere on Mars, but we have also seen that it is not eroding everywhere in the same way. There are clearly places where erosion is faster (feathers). »

MAVEN Mars Ion Escape (c)NASA

During a solar storm (right), Mars experiences a dramatic increase in atmosphere loss, compared with normal solar wind conditions (left). Artist's concept. Credit: NASA/GSFC

And the first conclusions of the researchers were at the very least unexpected: currently, Mars would lose 2 to 3 kilos of atmosphere... per second! « This rather impressive figure is the result of two things, says the young researcher. First, the amount of atmosphere that remains (the more there is, the faster it can be eroded) and second, the activity of the sun (the more active it is, the greater the erosion will be)". By extrapolating the figures obtained recently from the fact that we know that the erosion suffered by Mars was more important in the past, researchers have come to the conclusion that the planet was able - billions of years ago - to lose up to 150 kilos of atmosphere per second ! These figures make you dizzy but should not lead to hasty conclusions.

Although we now know how to quantify the loss of Mars' atmosphere, we cannot estimate the moment when the planet will be totally deprived of it. « Gaseous compounds escape from below the surface of Mars and can form atmospheric reservoirs, explains Arnaud Stiepen. That is why it is difficult to estimate the net escapement. The day Mars will have no atmosphere, the planet will be comparable to Mercury or the Moon, but we are still far from it. »  What then is the point of continuing to study this planet in decline on which we have little chance of finding traces of life as we know it on Earth? « Because we have always compared it to a little sister, close to the Earth on the scale of the solar system, of similar size (although about half the diameter), with seasonal and daily cycles close to those of the Earth, etc. Studying its evolution allows us to understand why it has gone wrong, concludes the researcher. As if we wished we could anticipate a not very enviable future for the Earth."  The MAVEN probe has fulfilled its mission but remains in working order. The NASA and University of Colorado team, leading this mission, will place it in a circular orbit in the coming years, which will stabilize it but more importantly allow it to continue analysis and serve as a relay antenna between the probes on Mars ground and Earth. 

Scientific reference

(1) Jakosky & al., Loss of the Martian atmosphere to space:  Present-day loss rates determined from MAVEN observations and integrated loss through time, Icarus, juin 2018.

Contact

STAR Institute - Space sciences, Technologies and Astrophysics Research
Laboratory for Planetary and Atmospheric Physics (LPAP) 

Arnaud STIEPEN - Arnaud.Stiepen@uliege.be I +32 4 3669769

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