NASA finds surprises about Martian atmosphere

Written by admin on 14/11/2018 Categories: 长沙桑拿

New NASA  research is shedding light on how and why Mars is the barren planet we know today.

Mars was once believed to have an ocean of water as well as flowing streams. But the Mars we have come to know today is a lifeless, barren, and dry world (though there is mounting evidence that Mars does indeed have water).

And that’s because it has very little atmosphere and almost no magnetic field to speak of.

NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, which has been orbiting the red planet since Sept. 21, 2014, has found evidence that challenges previously held beliefs about how Mars lost its valuable atmosphere.

This artist’s concept depicts the early Martian environment (left) – believed to contain liquid water and a thicker atmosphere – versus the cold, dry environment seen at Mars today (right).

NASA's Goddard Space Flight Center

Some of the interesting elements that the studies revealed are:

Powerful solar events, such as a coronal mass ejection —; an outpouring of particles from the sun that is carried along the solar wind —; have contributed to the stripping of the planet’s valuable atmosphere. This produced magnetic rotations that resulted in “rope-like tendrils” reaching up to 5,000 km into space and moving much faster than anticipated.

“Today’s planet is a cold, dry, desert-like environment, the atmosphere is thin, it’s not capable of holding liquid water at the surface today,” said Bruce Jakosky, MAVEN principle investigator. However, the Mars of millions of years ago was wet and quite possibly habitable. So what happened?

Unlike Earth, Mars’s has no global magnetic field, and because of that if a solar wind is strong enough, it able to strip it of the ions in the atmosphere (however, the particles don’t reach the surface of Mars). The ions are accelerated to escape velocity, thereby ripping the atmosphere from the planet.

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“It’s like a quarter pound of atmosphere escaping per second,” said Dave Brain, MAVEN co-investigator at theh Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, Boulder.

The solar wind interacts with the Mars upper atmosphere, but is deflected past Earth by a global magnetic field (artist’s concept).

NASA GSFC

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“I can’t help but think of hamburgers flying out of the atmosphere.”

Though it was believed that this was the case, MAVEN provided the first observational evidence of the process during a solar storm in March.

Could it happen here on Earth?

“Yes, Earth is losing atmospheric particles, but…Earth has a big global magnetic field to help [it],” said Brain.

He also included that in a long time, Earth’s magnetic field may one day shut off (it goes through shifts every few hundred years), but that won’t happen for a long time.

Bruce Jakosky, MAVEN principal investigator at the LASP stressed that Mars lost its atmosphere during the early life of the solar system when the solar wind was more powerful. In fact, they believe that it took place about 4.2 to 4.5 billion years ago.

A solar storm approaches Mars (artist’s concept). The Red Planet is thought to have lost much of its atmosphere to such extreme space weather.

NASA GSFC

The early Martian magnetic field did initially protect the planet from the solar wind, but when the magnetic field “turned off” it allowed the stripping of the atmosphere to take place. Today, the Martian atmosphere is about one per cent that of Earth’s.

Other findings include:

MAVEN detected carbon dioxide, argon and nitrogen dioxide in the planet’s upper atmosphere and higher amounts of oxygen than expected. The density of the elements also varied in each orbit. As well, researchers believe that the weak magnetic field is not only triggered by the solar wind but also Mars’ crust.Mars has aurora (northern lights in the northern hemisphere; the southern lights in the southern hemisphere), some of the lowest seen in our solar system, at an altitude of just 60 km (for comparison, Earth’s is anywhere from 80 km to higher than 600 km). But with Mars’ paltry magnetic field, these aurora are diffuse and driven by the magnetic field in the crust of Mars.

There are two types of auroras on Mars: one that is similar to Earth’s that occur at the poles, but weaker; the second one —; discovered by MAVEN —; in part of the atmosphere in regions that don’t have magnetic fields at all. The new auroras were seen in ultraviolet light, though they may be visible to the naked eye.

Dust has been found as high as 150 to 1,000 km in the atmosphere. Since no known process can lift dust that high into the atmosphere, it’s believed that the dust is of interplanetary origin.

The findings are important to helping scientists understand how planets interact with their host stars including exoplanets, or planets orbiting other stars.

The new findings appear in a special edition of the journal Science.

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