Solar Wind Rips Up Martian Atmosphere

Nov 21, 2008
Solar wind blowing against Mars tears atmosphere-filled plasmoids from the tops of magnetic umbrellas. Credit: Graphic artist Steve Bartlett.

Researchers have found new evidence that the atmosphere of Mars is being stripped away by solar wind. It's not a gently continuous erosion, but rather a ripping process in which chunks of Martian air detach themselves from the planet and tumble into deep space. This surprising mechanism could help solve a longstanding mystery about the Red Planet.

"It helps explain why Mars has so little air," says David Brain of UC Berkeley, who presented the findings at the 2008 Huntsville Plasma Workshop on October 27th.

Billions of years ago, Mars had a lot more air than it does today. (Note: Martian "air" is primarily carbon dioxide, not the nitrogen-oxygen mix we breathe on Earth.) Ancient martian lake-beds and river channels tell the tale of a planet covered by abundant water and wrapped in an atmosphere thick enough to prevent that water from evaporating into space. Some researchers believe the atmosphere of Mars was once as thick as Earth's. Today, however, all those lakes and rivers are dry and the atmospheric pressure on Mars is only 1% that of Earth at sea-level. A cup of water placed almost anywhere on the Martian surface would quickly and violently boil away—a result of the super-low air pressure.

So where did the air go? Researchers entertain several possibilities: An asteroid hitting Mars long ago might have blown away a portion of the planet's atmosphere in a single violent upheaval. Or the loss might have been slow and gradual, the result of billions of years of relentless "sand-blasting" by solar wind particles. Or both mechanisms could be at work.

Brain has uncovered a new possibility--a daily ripping process intermediate between the great cataclysm and slow erosion models. The evidence comes from NASA's now-retired Mars Global Surveyor (MGS) spacecraft.

In 1998, MGS discovered that Mars has a very strange magnetic field. Instead of a global bubble, like Earth's, the Martian field is in the form of magnetic umbrellas that sprout out of the ground and reach beyond the top of Mars' atmosphere. These umbrellas number in the dozens and they cover about 40% of the planet’s surface, mainly in the southern hemisphere.

For years, researchers thought the umbrellas protected the Martian atmosphere, shielding pockets of air beneath them from erosion by the solar wind. Surprisingly, Brain finds that the opposite can be true as well: "The umbrellas are where coherent chunks of air are torn away."

Addressing his colleagues at the Workshop, he described how he made the discovery just a few months ago:

Brain was scrolling through archival data from Global Surveyor's particles and fields sensors. "We have measurements from 25,000 orbits," he says. During one of those orbits, MGS passed through the top of a magnetic umbrella. Brain noticed that the umbrella's magnetic field had linked up with the magnetic field in the solar wind. Physicists call this "magnetic reconnection." What happened next is not 100% certain, but Global Surveyor's readings are consistent with the following scenario: "The joined fields wrapped themselves around a packet of gas at the top of the Martian atmosphere, forming a magnetic capsule a thousand kilometers wide with ionized air trapped inside," says Brain. "Solar wind pressure caused the capsule to 'pinch off' and it blew away, taking its cargo of air with it." Brain has since found a dozen more examples. The magnetic capsules or "plasmoids" tend to blow over the south pole of Mars, mainly because most of the umbrellas are located in Mars' southern hemisphere.

Brain isn't ready to declare the mystery solved. "We're still not sure how often the plasmoids form or how much gas each one contains." The problem is, Mars Global Surveyor wasn't designed to study the phenomenon. The spacecraft was only equipped to sense electrons, not the heavier ions which would make up the bulk of any trapped gas. "Ions and electrons don't always behave the same way," he cautions. Also, MGS sampled the umbrellas at fixed altitudes and at the same local time each day. "We need to sample many altitudes and times of day to truly understand these dynamic events."

In short, he told the audience, "we need more data."

Brain is pinning his hopes on a new NASA mission named MAVEN. Short for "Mars Atmosphere and Volatile Evolution," MAVEN is an upper atmosphere orbiter currently approved for launch to Mars in 2013. The probe is specifically designed to study atmospheric erosion. MAVEN will be able to detect electrons, ions and neutral atoms; it will be able to measure both magnetic and electric fields; it will travel around Mars in an elliptical orbit, piercing magnetic umbrellas at different altitudes, angles, and times of day; and it will explore regions both near and far from the umbrellas, giving researchers the complete picture they need.

If magnetized chunks of air are truly being torn free, MAVEN will see it happening and measure the atmospheric loss rate. "Personally, I think this mechanism is important," says Brain, "but MAVEN may yet prove me wrong."

Meanwhile, the Mystery of the Missing Martian Air is shaping up to be a ripping good yarn.

Source: Dr. Tony Phillips, Science@NASA

Explore further: New Horizons spacecraft experiences anomaly

Related Stories

Will we ever colonize Mars?

Jun 01, 2015

Mars. It's a pretty unforgiving place. On this dry, dessicated world, the average surface temperature is -55 °C (-67 °F). And at the poles, temperatures can reach as low as -153 °C (243 °F). Much of ...

Does the red planet have green auroras?

May 14, 2015

Martian auroras will never best the visual splendor of those we see on Earth, but have no doubt. The red planet still has what it takes to throw an auroral bash. Witness the latest news from NASA's MAVEN ...

Why can't we design the perfect spacesuit?

Feb 19, 2015

So far, every spacesuit humans have utilized has been designed with a specific mission and purpose in mind. As of yet, there's been no universal or "perfect" spacesuit that would fit every need. For example, ...

Cassini catches Titan naked in the solar wind

Jan 29, 2015

(Phys.org)—Researchers studying data from NASA's Cassini mission have observed that Saturn's largest moon, Titan, behaves much like Venus, Mars or a comet when exposed to the raw power of the solar wind. ...

First light for MAVEN (w/ Video)

Oct 13, 2014

After 10-month voyage across more than 400 million miles of empty space, NASA's MAVEN spacecraft reached Mars on Sept. 21st 2014. Less than 8 hours later, the data started to flow.

Recommended for you

Uranus' moon Titania

12 hours ago

Like all of the Solar Systems' gas giants, Uranus has an extensive system of moons. In fact, astronomers can now account for 27 moons in orbit around Uranus. Of these, none are greater in size, mass, or surface ...

Image: Europa's blood-red scars

12 hours ago

Jupiter's moon Europa is a bizarre place. There is something undeniably biological about this image, sent back by NASA's Galileo spacecraft – the moon is scarred by deep red gashes, resembling the vibrant ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

ACW
2 / 5 (1) Nov 21, 2008
Ahem. It is obvious that the Martian atmosphere has been stripped away, probably by both of the aforementioned processes. The question is whether we can reverse or slow the process to improve the conditions on Mars.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.