A robotic detective of sorts is being dispatched to Mars to try to crack a long-standing mystery of why a planet that seems to have once been Earth's twin, with oceans, rivers, rain and snow, ended up a cold desert.
"We know for a fact that it used to be very different. Mars used to have a wet climate ... but over billions of years that changed," said astronomer Michelle Thaller, with NASA's Goddard Space Flight Center in Greenbelt, Md.
Scientists believe the climate change happened because Mars lost its magnetic shield, leaving the planet vulnerable to solar and cosmic radiation. Over time, the ionizing rays took apart what was believed to have been a thick, protective atmosphere which kept Mars warm and wet.
NASA's Curiosity rover and other probes have given scientists a glimpse of ancient Mars by analyzing its rocks. The new scout, called MAVEN, will study what remains of Mars' atmosphere to learn about processes that are going on today.
"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 Pan Conrad, a deputy principal scientist on the Curiosity mission.
MAVEN, an acronym for Mars Atmosphere and Volatile Evolution Mission, is designed to spend at least on year circling Mars, focusing not on the planet's surface but on the thin layer of gases that remains in its skies.
Scientists want to know how cosmic rays and high-energy particles from the sun, which blast out into space during solar flares and powerful storms, peel away Mars' atmosphere and how often the damage occurs.
One of MAVEN's three science instruments is a near-copy of one of Curiosity's gas analyzers, allowing the spacecraft to inhale the atmosphere and reveal its chemical composition.
The information should help scientists home in on the time in Mars' history when conditions were most suitable for life.
"If live arose on Mars it probably did so early, within about 500 million years," of its formation, Conrad said.