Heat and dust help launch Martian water into space, scientists say

Scientists using an instrument aboard NASA’s Mars Atmosphere and Volatile EvolutioN, or MAVEN, spacecraft have found that water vapor near the surface of the Red Planet is projected higher into the atmosphere than what we expected. There, it is easily destroyed by electrically charged gas particles – or ions – and lost into space.

The researchers said the phenomenon they discovered was one of many that caused Mars to lose the equivalent of a global ocean of water to hundreds of feet (or hundreds of meters) from depth over billions of years. Report on their discovery on November 13 in the newspaper Science, the researchers said Mars continues to lose water today, as vapor is carried to high altitudes after being sublimated by the frozen polar caps during warmer seasons.

“We were all surprised to find water so high in the atmosphere,” said Shane W. Stone, a doctoral student in planetary science at the Lunar and Planetary Laboratory at the University of Arizona in Tucson. “The measurements we used could only have come from MAVEN as it hovered in the atmosphere of Mars, above the planet’s surface.”

To make their discovery, Stone and his colleagues relied on data from MAVEN’s Neutral Gas Ion Mass Spectrometer (NGIMS), which was developed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The mass spectrometer inhales air and separates the ions that compose it by their mass, this is how scientists identify them.

Stone and his team have tracked the abundance of water ions above Mars for more than two Martian years. In doing so, they determined that the amount of water vapor near the top of the atmosphere about 93 miles, or 150 kilometers, above the surface is highest during summer in the southern hemisphere. During this time, the planet is closest to the Sun, and therefore warmer, and dust storms are more likely to occur.

Hot summer temperatures and strong winds associated with dust storms help water vapor reach the higher parts of the atmosphere, where it can easily be broken down into oxygen and hydrogen. The hydrogen and oxygen then escape into space. Previously, scientists believed that water vapor was trapped near the Martian surface as on Earth.

“Anything that reaches the upper atmosphere is destroyed, on Mars or on Earth,” Stone said, “because that’s the part of the atmosphere that is exposed to the full force of the Sun.”

Researchers measured 20 times more water than usual for two days in June 2018, when a severe global dust storm enveloped Mars (the one that shut down NASA’s Opportunity rover). Stone and his colleagues estimated that Mars lost as much water in 45 days during this storm as during a whole Martian year, which lasts two Earth years.

“We have shown that dust storms interrupt the water cycle on Mars and push water molecules higher into the atmosphere, where chemical reactions can release their hydrogen atoms, which are then lost in the atmosphere. ‘space,’ said Paul Mahaffy, director of the Solar System Exploration division. at NASA Goddard and NGIMS Principal Investigator.

Other scientists have also discovered that Martian dust storms can lift water vapor far above the surface. But no one had realized until now that the water would reach the top of the atmosphere. There are abundant ions in this region of the atmosphere that can break down water molecules 10 times faster than they are destroyed at lower levels.

“What is unique about this discovery is that it provides us with a new path that we didn’t think existed for water to escape from the Martian environment,” said Mehdi Benna, a scientist. planetary researcher of Goddard and co-investigator of the NGIMS instrument of MAVEN. “This will fundamentally change our estimates of how fast water escapes today and how fast it escapes in the past.”