A team of “planetary chemists” from the US has figured out the process behind Mars’s unexplained loss of water. Billions of years ago, the Red Planet is believed to have resembled a young Earth, with a hot and humid climate, and oceans of liquid water. These conditions have given rise to the theory simple microbial life may have developed on Mars – a theory NASA’s Perseverance rover was launched to explore.
Today, however, Mars is cold and desolate, with the only signs of water found in the form of ice at the south pole and in the form of water vapour in the atmosphere.
Scientists at the University of Arizona have been working on this conundrum under the leadership of graduate student Shane Stone in the UArizona Lunar and Planetary Laboratory.
Since 2014, Mr Shane has been working on the NASA Mars Atmosphere and Volatile EvolutioN or MAVEN mission.
Launched in 2013, MAVEN is a spacecraft designed to investigate the Red Planet’s upper atmosphere.
And it was this instrument that helped the Arizona scientists discover how heat and dust help launch Mars’s water vapour into space.
Mr Shane said: “We know that billions of years ago, there was liquid water on the surface of Mars.
“There must have been a thicker atmosphere, so we know that Mars lost the majority of its atmosphere to space.
“MAVEN is trying to characterise the process responsible for this loss, and one portion of that is understanding exactly how Mars lost its water.”
Mr Shane and his colleagues presented their findings on November 13 in the journal Science.
The scientists described processes by which water vapour near the planet’s surface is carried higher into the atmosphere than anyone expected.
Once the water vapour reaches high enough, it is destroyed by electrically charged gas particles and vented into space.
Mr Shane said: “We were all surprised to find water so high in the atmosphere.
“The measurements we used could have only come from MAVEN as it soars through the atmosphere of Mars, high above the planet’s surface.”
According to the researchers, the phenomenon is just one of several that caused Mars to lose an ocean of water hundreds of feet deep over billions of years.
And in their study they found the newly-described process can account for the loss of a global ocean about 17 inches deep, going one billion years into the past.
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Data collected by MAVEN, paired with observations by the Hubble Space Telescope showed the loss of water varies with the seasons.
The MAVEN orbiter dips into the planet’s atmosphere every four-and-a-half hours.
Instruments aboard MAVEN then measure the levels of charged water particles in the atmosphere, some 100 miles above the planet’s surface.
According to Mr Stone, Mars’s oval-shaped orbit is to blame: when Mars is closest to the Sun, the planet warms and more ice water moves from the surface to the highest reaches of the atmosphere where it is lost to space.
This happens once every Martian year – the equivalent of 687 days.
The process is exacerbated by annual dust storms and every 10 years when planet-wide storms envelop Mars, leading to more heating in the atmosphere.
Mr Stone said: “If we took water and spread it evenly over the entire surface of Mars, that ocean of water lost to space due to the new process we describe would be over 17 inches deep.
“An additional 6.7 inches would be lost due solely to the effects of global dust storms.”
The processes also challenge previously held assumptions about Mars losing its water at a much slower pace, caused by the sun’s rays destroying gaseous water in the lower atmosphere.
Mr Stone said: “The loss of its atmosphere and water to space is a major reason Mars is cold and dry compared to warm and wet Earth.
“This new data from MAVEN reveals one process by which this loss is still occurring today.”
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