NASA

Mars owes its dry and dusty appearance

to its wispy atmosphere, less than 1 percent of the thickness of the Earth's. But it wasn't always that way: The Red Planet formerly had a much thicker atmosphere that probably allowed for liquid water on the surface, an atmosphere that was depleted when the planet's magnetic field faded away. What the heck happened? Planetary scientists have been wondering for years, but NASA is hoping to use tools aboard a new orbiting spacecraft called MAVEN to figure out what changed on Mars, and why it lost the water we now know it had as a younger planet.

Researchers once hoped that they'd find evidence that Mars' water had gone down into the planet's crust, but results have been scarce. Instead, scientists now think Mars lost its global magnetic field, which would have surrounded the entire planet the way Earth's does today, billions of years ago, allowing the water to disappear in another direction entirely. Without the protection of the magnetic field, much of the atmosphere dissipated into the vacuum of space. All that's left are patches of magnetic field, which create pockets of atmosphere.

NASA scientists wager that if they can study the effect of solar winds on the unprotected spots, they can analyze just how much damage the winds have caused over time—and perhaps paint a picture of the atmosphere Mars had before losing its magnetic field.

Starting later this year, the Mars Atmosphere and Volatile Evolution mission (MAVEN) will carry a highly sensitive magnetic-field instrument to study the Martian upper atmosphere. This magnetometer, described by mission co-investigator Jack Connerney as "like an electric compass" that can measure both the strength and direction of a magnetic field, is made up of a series of coils, each containing a magnetic ring wrapped around a metal core. The sensors, called "fluxgates," become saturated more quickly the closer they are to a magnetic field, causing an imbalance that reveals the field's presence.

The magnetometer is so sensitive that researchers worried the magnetic field of the spacecraft itself might set it off. To be safe, the device is located on the very farthest tip of the craft's solar array.

NASA

"The MAVEN magnetometer is key to unraveling the nature of the interactions between the solar wind and the planet," says MAVEN principal investigator Bruce Jakosky from the University of Colorado at Boulder's Laboratory for Atmospheric and Space Physics. And with that information, researchers hope to better understand the climate—both of the present and of billions of years in the past—of our closest planetary neighbor.

"A lot of the measurements from the Mars missions over the past couple of decades have shown good evidence that the planet had water at some time, but the climate today is too thin, cold, and dry to support it," Jakosky tells PM. "We're trying to answer the question of where the water went."

Eight instruments in total will measure the energy input to the planet from the sun and solar winds, how that energy effects the atmosphere, and the escape path of ions into space. If they can see how fast gas is escaping now, they can project that backward to find answers. "If we can find out how much gas has escaped from the atmosphere over time," Jakosky says, "we can figure out if that was, in fact, the driving process in changing the planet's climate."

"That's what we're really getting at—climate change." Jakosky says. "We won't be able to answer that overarching question of whether there was life on Mars, but we will understand how it lost what habitability it once had."

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