What happened to Mars? A planetary mystery

NASA’s MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft, inside a payload fairing, is hoisted to the top of a United Launch Alliance Atlas V rocket at the Vertical Integration Facility at Cape Canaveral Air Force Station’s Space Launch Complex 41. The move and hoisting operations mark another major milestone for the launch team as everything proceeds on schedule to launch Nov. 18, when the Atlas V will lift MAVEN into space and on to Mars. The two-hour launch window extends from 1:28 to 3:28 p.m. EST. MAVEN is the first spacecraft devoted to exploring and understanding the Martian upper atmosphere. It will orbit the planet in an elliptical orbit that allows it to pass through and sample the entire upper atmosphere on every orbit. The spacecraft will investigate how the loss of Mars’ atmosphere to space determined the history of water on the surface. Credit: NASA

Billions of years ago when the planets of our solar system were still young, Mars was a very different world. Liquid water flowed in long rivers that emptied into lakes and shallow seas. A thick atmosphere blanketed the planet and kept it warm. In this cozy environment, living microbes might have found a home, starting Mars down the path toward becoming a second life-filled planet next door to our own. But that’s not how things turned out.

Today, Mars is bitter cold and desiccated. The planet’s thin, wispy atmosphere provides scant cover for a surface marked by dry riverbeds and empty lakes. If Martian microbes still exist, they’re probably eking out a meager existence somewhere beneath the dusty Martian soil. What happened? This haunting question has long puzzled scientists. To find the answer, NASA is sending a new orbiter to Mars called MAVEN (Mars Atmosphere and Volatile Evolution).

“The goal of MAVEN is to figure out what processes were responsible for those changes in Martian climate,” says Bruce Jakosky, Principal Investigator for MAVEN at the University of Colorado at Boulder.

Scheduled for launch in Nov. 2013, and due to arrive in Sept. 2014, MAVEN is bristling with instruments to study Mars’ upper atmosphere. That’s where many researchers believe the answer lies.

The only way Mars could have been wet and warm 4 billion years ago, is if it also had a thick atmosphere. CO2 in the Martian atmosphere is a greenhouse gas, just as it is in our own atmosphere. A thick blanket of CO2 and other greenhouse gases would have provided the warmer temperatures and greater atmospheric pressure required to keep liquid water from freezing solid or boiling away.

Something caused Mars to lose that blanket. One possibility is the solar wind. Unlike Earth, Mars is not protected by a global magnetic field. Instead, it has “magnetic umbrellas” scattered around the planet that shelter only part of the atmosphere. Erosion of exposed areas by solar wind might have slowly stripped the atmosphere away over billions of years. Recent measurements of isotopes in the Martian atmosphere by Mars rover Curiosity support this idea: light isotopes of hydrogen and argon are depleted compared to their heavier counterparts, suggesting that they have floated away into space. Via What happened to Mars? A planetary mystery.

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