The prime suspect is the sun, which has been peeling away the planet's atmosphere, molecule by molecule, for billions of years. (Agencies)
Exactly how that happens is the goal of NASA's new Mars Atmosphere and Volatile Evolution Mission, or MAVEN, which is scheduled for launch at 1:28 pm EST/1828 GMT on Monday from Cape Canaveral Air Force Station in Florida.
Upon arrival in September 2014, MAVEN will put itself into orbit around Mars and begin scrutinizing the thin layer of gases that remains in its skies.
"MAVEN is going to focus on trying to understand what the history of the atmosphere has been, how the climate has changed through time and how that has influenced the evolution of the surface and the potential habitability - at least by microbes - of Mars,' said lead scientist Bruce Jakosky, with the University of Colorado at Boulder.
Specifically, MAVEN will look at how much and what type of radiation is coming from the sun and other cosmic sources and how that impacts gases in Mars' upper atmosphere.
Scientists have glimpsed the process from data collected by Europe's Mars Express orbiter and NASA's Curiosity rover, but never had the opportunity to profile the atmosphere and space environment around Mars simultaneously.
"We'll get a window on what is happening now so we can try and look backward at the evidence locked in the rocks and put the whole story together about Martian history and how it came to be such a challenging environment," said Mars scientist Pan Conrad, with NASA's Goddard Space Flight Center in Greenbelt, Maryland.
The prime suspect is the sun, which has been peeling away the planet's atmosphere, molecule by molecule, for billions of years.