Scientists believe they have finally found out what happened to the water on Mars

How did Mars lose its water? It is one of the solar system’s most enduring mysteries on one of its most intriguing planets.

Now, thanks to NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, scientists have gained a richer understanding of the Martian atmosphere, getting to the heart of how the planet works – and they believe they have an answer for it. ‘enigma.

To figure out where Martian water was going, scientists looked up – just over 92 miles, or 150 kilometers above the Martian surface, to be precise. What they found is detailed in a new study published Thursday in the journal Science.

Shane Stone is a planetary scientist at the University of Arizona and one of the authors of the new study. Looking at that specific part of the planet’s atmosphere, rather than its surface, was key to scientists’ new understanding of what happened to its water, he says. Reverse.

“This is the part of the atmosphere where we move from atmosphere to space. It’s not a hard edge, but a smooth transition, ”says Stone.

All planets with an atmosphere, including Earth, have this transient space. The Earth is known as the exosphere. This is where starlight breaks down neutral molecules into their constituent parts, like carbon dioxide into carbon and hydrogen.

And it was in this transitional space that Stone’s team found traces of water.

“It’s a real surprise and has important implications for understanding the escape of water from the planet,” says Stone.

Dust devils – Dust storms rising from the Martian surface appear to have slowly sucked water from the planet over millions of years, sweeping up water molecules on a wild journey through the atmosphere, new data shows. . This also happens on Earth – evaporated water molecules travel upward until they condense from gas to liquid, becoming rain-filled clouds. Where this process occurs is known as hygropause.

“On Mars, hygropause doesn’t work as efficiently as it should, not as efficiently as Earth’s hygropause,” Stone says. As a result, as water moves through Mars’ upper atmosphere, it reacts with molecules in the atmosphere and breaks down into hydrogen and oxygen – the hydrogen can then escape entirely from the Martian atmosphere, the study suggests – and is ultimately lost in space forever.

The findings shed light on the evolution of the Red Planet from a humid world, perhaps similar to Earth, to the desert world we know today. Scientists believe that if the Martian surface is riddled with ancient lake and river beds, the only remaining water may be trapped underground.

Martian weather – MAVEN can conduct research during Martian dust storms. While most other satellites take circular orbits, meaning they are looking at the same part of Mars at the same time of day, over and over again, MAVEN “continually samples different conditions on Mars, in terms of hours. of the day, longitude and latitude, ”Stone said.

The Red Planet regularly experiences regional dust storms, but in 2018 the planet was overtaken by a global dust storm. Stone describes the event as “very lucky” for the team, as it provided an unprecedented view of how the entire planet is responding to a storm.

Not everyone would call the storm of 2018 “lucky”. While MAVEN was busy staring at the sky, NASA Opportunity rover patrolled the Martian surface. Dust storms have set in Opportunitythe rover’s solar panels, blocking the sun’s rays and depriving it of energy – ultimately putting an end to the rover’s historic journey.

“We were absolutely thrilled when we had this dust storm… give and take,” says Stone.

Abstract: Mars has lost most of its once abundant water in space, leaving the planet cold and dry. In standard models, molecular hydrogen produced from water in the lower atmosphere diffuses into the upper atmosphere where it is dissociated, producing atomic hydrogen, which is lost. Using observations from the neutral gas mass spectrometer on the Mars Atmosphere and Volatile Evolution spacecraft, we demonstrate that instead, water is transported directly to the upper atmosphere and then dissociated by ions to produce atomic hydrogen. . The abundance of water in the upper atmosphere varied seasonally, peaking in the southern summer and increasing during dust storms, including the global dust storm of 2018. We calculate that this transport of water dominates the current loss of atomic hydrogen in space and has influenced the evolution of the climate of Mars