How did Mars get so cold and dry? MAVEN may tell us

The MAVEN spacecraft, an acronym for Mars Atmosphere and Volatile Evolution, sits atop an Atlas rocket at Florida’s Cape Canaveral ready for launch this afternoon. Click to watch live NASA TV broadcast. Credit: NASA/Jim Grossman

At 12:28 p.m. CST today NASA’s MAVEN spacecraft successfully lifted off on a 10-month journey to Mars. Next September it will enter orbit and study the planet’s atmosphere over the course of at least a year.

Artist’s view of MAVEN in orbit come next September. Credit: NASA/GSFC

The key question the probe will attempt to answer is how the Red Planet became so inhospitable. We know from our landers and orbiters that water once flowed in streams and great floods across the now barren landscape.

All the evidence is there: winding river courses, islands eroded into teardrop shapes by powerful currents and water-deposited mineral veins lining cracks inside rocks. Layered clay sediments have been found in Gale Crater, and the Curiosity Rover ran across rocks rounded and tumbled into pebbles by the action of flowing water.


Cool video simulation showing Mars evolving from a wet planet to the current cold desert 

I could go on and on. So what happened to all the water?  In order for water to flow across a planet’s surface you need air or more specifically, atmospheric pressure. If the air’s too thin, there’s not enough pressure pushing down on it to prevent it from simply boiling away. Thin air also means colder temperatures.

Water once flowed in this ancient riverbed on Mars. Credit: NASA

Next time you’re flying in a plane at a typical cruising altitude of 35,000 feet, consider that just outside the door, the temperature is close to 70 below F (-55 C) even on a summer day. That’s because the air thins and pressure drops the higher you go. With fewer molecules bouncing around to create what we feel as heat, it’s darn cold up there. Air at the surface is not only denser (holds heat better) but it’s also warmed by its contact with the ground.

When Mars’ atmosphere went from thick to thin perhaps 2-3 billion years ago, some of the water holed up in the polar ice caps, dust-covered glaciers and underneath the soil. But much of it, along with the Martian air, took another route. Some of the original carbon dioxide became incorporated in the crust as carbonate rocks, but scientists theorize that most of it was stripped away by a steady blast of particles from the sun called the solar wind.

The present atmosphere of Mars is less than 1% the thickness of Earth’s atmosphere. Our blanket of air has protection from a planetary magnetic field that sloughs most of those solar blizzards away. Not so with Mars. The planet possesses no overall magnetic field, so the sun’s flow of high speed electrons and protons can pluck precious atmospheric gases away a molecule at a time until there’s too little left to warm the planet and provide the pressure needed for water to flow.

It’s hypothesized that without a global magnetic field, the solar wind stripped Mars of much of its atmosphere. Credit: NASA

Mars may have lost its magnetic armor when its core cooled down. Within Earth’s core, molten iron rises, cools, sinks and rises again in a process called convection. This movement, coupled with our planet’s spin, generates a magnetic field. Mars likely had a similar field early in its history, but somehow convection stopped in its core. Did the core cool and solidify or was it disrupted by an asteroid impact? We don’t know. For whatever reason, once the air supply dwindled, the water froze or vaporized, water stopped flowing and planet got the chills. The average temperature on Mars today is 81 below zero F (-63 C). Compare that to Earth’s 61 degrees F (16 C).

That’s why MAVEN’s on it way to Mars – to sniff out clues from the atmosphere so we can find out “the rest of the story”.

Going along for the ride is a DVD attached to one of the spacecraft’s solar panels. It contains over 100,000 names of people who signed up for the ride and over 1,000 Japanese haiku verses. The number one haiku vote getter was submitted by Benedict Smith of Great Britain:

“It’s funny, they named/Mars after the God of War/Have a look at Earth.”

Click HERE to watch the launch live.

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