Probe to explore riddle of Mars’ missing air

The New York TimesNovember 16, 2013 


An undated rendering of the Mars Atmosphere and Volatile Evolution probe in orbit over Mars. The spacecraft, called MAVEN for short, is scheduled to launch Monday, Nov. 18, 2013, from Cape Canaveral, Fla., beginning its 10-month journey to Mars, searching its atmosphere for clues of whether the planet could have been, perhaps four billion years ago, a friendly place for life. (NASA/GSFC via The New York Times) -- NO SALES; FOR EDITORIAL USE ONLY WITH STORY SLUGGED MARS MISSING AIR BY KENNETH CHANG. ALL OTHER USE PROHIBITED.


NASA’s next mission to Mars aims to answer one question: What happened to the air that once made the surface habitable?

That is the latest piece in the scientific exploration of whether Mars could have been, perhaps 4 billion years ago, a place friendly for life.

The answer may come from a space probe known as Mars Atmosphere and Volatile Evolution, or MAVEN for short, which is ready for the launching pad at Cape Canaveral, Fla., and poised to lift off Monday at 1:28 p.m. After a 10-month journey, the spacecraft is to enter orbit around Mars and spend at least a year observing Mars’ atmosphere.

“It’s clear that major questions about the history of Mars center on the history of its climate and atmosphere, and how that’s influenced the surface, the geology and on the possibility for life,” Bruce M. Jakosky, a professor of geological sciences at the University of Colorado who is MAVEN’s principal investigator, said at a NASA news conference last month.

Planetary scientists believe that young Mars was blanketed with a thick layer of air - heat-trapping carbon dioxide, in particular - that kept it warmer and wetter. Ancient channels on Mars look as if they were carved by flowing water.

Sometime between then and now, the atmosphere went away, and Mars today is an airless, frigid desert with average surface temperatures of minus 64 degrees Fahrenheit.

The once-bountiful air molecules must have either gone up, escaping into space, or down, transformed by chemical reactions into rock. Hydrogen, the lightest of gases, can simply float away from gravity’s grasp. Heavier molecules like oxygen and carbon dioxide might have been knocked out by particles and radiation streaming from the sun.

“As the solar wind sweeps by, it is able to strip off the atmospheric gas,” Jakosky said. “It’s actually stripped away, molecule by molecule, atom by atom.”

To figure out the puzzle of the missing atmosphere, MAVEN will measure the wisps that remain.

The spacecraft - which will widen to the length of a school bus after it fans out its solar arrays - will loop Mars in an elliptical, 4.5-hour orbit, climbing 3,860 miles above the planet and then swooping down to within 93 miles to the surface.

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