New confirmations of the solar wind role in the loss of Mars’ atmosphere

Artist's concept comparing Mars as it is today and as it was 4 billion years ago (Image NASA’s Goddard Space Flight Center)
Artist’s concept comparing Mars as it is today and as it was 4 billion years ago (Image NASA’s Goddard Space Flight Center)

An article published in the journal “Science” describes a research on the atmosphere of the planet Mars that indicates the Sun’s wind and radiation as the principal culprits of the fact that today that atmosphere is so thin. A team led by Bruce Jakosky, principal investigator of NASA’s MAVEN space probe’s mission, examined the measurements of the existing gases estimating for example that 65% of argon present origininally got lost in space. This research confirms the one published in November 2015.

The MAVEN space probe entered Mars’ orbit in September 2014 exactly with the main goal of studying its atmosphere and see why today is so thin. For some time we’ve known that about 4 billion years ago there was liquid water on the red planet’s surface so there had to be a much thicker atmosphere that ensured temperature and pressure conditions impossible today.

In November 2015, the MAVEN mission team announced the results of the first study, which indicated that the gases in the Martian atmosphere had gone largely lost in space due to solar wind. The measurements from the space probe went on to better understand the mechanisms of this phenomenon and now researchers have presented the results of today’s atmospheric measurements, used to provide an estimate of how much gas got lost over time.

The researchers measured for example two isotopes of argon, which can only be lost by being pushed into the space by solar wind and radiation because it’s a noble gas, so it doesn’t react with other elements that may sequester it in the soil. Argon36 is lighter of Argon38 so is more likely to be brought in the higher layers of Mars’ atmosphere and get lost into space, leaving a greater percentage of the heavier isotope.

The measurement of the amounts of the two isotopes of argon carried out by both MAVEN space probe in the higher layers of the atmosphere and by the Mars Rover Curiosity on the surface make it possible to estimate the percentage of this gas that got lost in the course of time, which was determined around 65%.

This type of estimate can be used to evaluate the loss of other elements and also of molecules. In particular, the scientists were interested in carbon dioxide, a greenhouse gas that 4 billion years ago maybe was critical to have environmental conditions similar to those on Earth.

In the case of carbon dioxide, the problem is that it can be removed from the atmosphere by various processes, so a part might have been sequestered in the soil. As a result, the researchers have confirmed that most of this gas is lost in space due to the solar wind, but this is a minimum estimate.

This study was conducted using in particular the data detected by the MAVEN space probe’s Neutral Gas and Ion Mass Spectrometer (NGIMS) instrument and by the Mars Rover Curiosity’s Sample Analysis at Mars (SAM) instrument. Two independent missions provided useful data in a research for a synergy that has gave us more information about the changes that happened on Mars.

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