Mars' upper atmosphere is slowly leaking out into the cosmos, according to new data gathered from NASA's MAVEN spacecraft. The cause of this great escape is our Sun; solar winds from the star constantly slam into Mars and strip away the atmosphere's outer layers.

NASA scientists figured this out after studying how a solar storm impacted Mars earlier this year. The solar particles from the storm energized the gases in the upper atmosphere, causing them to streak out into space. The researchers also studied the types of atoms and molecules being lost from Mars' atmosphere, which included hydrogen, oxygen, and carbon dioxide. All of these findings and more were published today in a swath of studies in both Science and Geophysical Research Letters, based on the data gathered by MAVEN over the past year.

It may explain why Mars is so different from the planet it used to be

This solar interaction may explain why Mars is so different from the planet it used to be, according to NASA scientists. Researchers believe that Mars had a thick atmosphere over 4 billions years ago, filled with enough gasses to warm up the planet and foster large, liquid oceans on the surface. Now, Mars is a cold, ocean-less planet with a thin atmosphere that's a hundredth the pressure of Earth's. These new observations from the MAVEN mission suggest the Sun has likely been the source of this atmosphere loss. Solar winds have been slowly chipping away at the atmosphere over time, allowing gases — and water from the ancient oceans — to escape the planet.

"One of the major questions is where did the water go?" said Bruce Jakosky, MAVEN's principal investigator at the University of Colorado's Laboratory for Atmospheric and Space Physics. "MAVEN is trying to understand what role the escape of the atmosphere has played in the change of the climate."

NASA's MAVEN spacecraft launched aboard an Atlas V rocket in November 2013 and inserted itself into orbit around Mars in September 2014. Since then, the probe has been diving periodically into the atmosphere to figure out what's going on inside. MAVEN — or the Mars Atmosphere and Volatile Evolution mission — is equipped with eight instruments, including solar wind analyzers and a magnetometer, to characterize how the various particles around Mars interact.

The research team used these instruments to see what happened to Mars' atmosphere during a coronal mass ejection on March 8th. A coronal mass ejection is a huge burst of charged gas that shoots out periodically from the Sun. When the solar winds hit Mars in March, they wrapped around the planet, heating up the atmospheric gases and causing them to shoot outward. Overall, the solar storm significantly amplified the amount of gasses that the atmosphere lost. "We saw the loss rate go up by a factor of 10 or 20," said Jakosky.

A primitive ocean on Mars held more water than Earth's Arctic Ocean. (NASA)

These coronal mass ejections are likely to blame for significantly altering the Red Planet. NASA researchers believe that about 4.3 billion years ago, Mars had huge oceans, with enough water to cover the planet's entire surface in a liquid layer 450 feet deep. That's more water than what's found in Earth's Arctic Ocean. Such huge bodies of water would have required Mars to have a much thicker and denser atmosphere than it does now.

At some point in Mars' history, there was a dramatic climate shift

That means at some point in Mars' history, there was a dramatic climate shift. Jakosky says this was likely triggered by the loss of Mars' magnetic field. Mars once had a swirling, molten iron core — just like Earth does today — and the movement of this electrically conducting material generated a magnetic field around the planet. This field, called a magnetosphere, protected Mars from damage by solar winds, just as Earth's magnetosphere protects us now. The field deflects incoming particles from the Sun and redirects them toward areas where the magnetic field is weakest — the planet's poles.

But billions of years ago, Mars' iron core froze and the strong, intrinsic magnetic field was lost. Mars still has a magnetic field today, but it’s puny, and stems from magnetized rocks in the planet’s southern hemisphere. Mars’ current magnetosphere is about 40 times weaker than Earth's, making Mars much more susceptible to damage from solar flares. "So the turn off of Mars' magnetic field triggered the turn on of the solar wind stripping away the atmosphere," said Jakosky.

As Mars lost more of its atmospheric gases — such as heat-trapping carbon dioxide — the planet grew colder and could no longer support such huge amounts of liquid on its surface. This explains why we don't see abundant oceans anymore, but researchers have been confused about where all that water went. Scientists know that there's frozen water in the polar ice caps and there is some water bound up in the Martian soil, as well as small amounts of liquid water on the surface. But the vast majority of the water is missing.

Mars seemingly has a global aurora

MAVEN has also solved that mystery: the water escaped out into space along with the rest of the atmosphere. During one of its dives, the spacecraft detected significant amounts of oxygen in Mars' upper atmosphere. Since hydrogen has also been observed in this region before, MAVEN researchers think that Mars' oceans must have evaporated and then slowly leaked out into space over billions of years. "It's consistent with the loss of water — measuring both hydrogen and oxygen in this reservoir," said MAVEN scientist Stephen Bougher, a planetary scientist at the University of Michigan.

One interesting side effect of all this atmosphere loss is that Mars seemingly has a global aurora, similar to the ones near Earth's poles. Since there's no big magnetic field to stop incoming particles, solar winds bombard the atmosphere all over the planet's surface, glowing brightly, according to new MAVEN data. "It's just a shame there's no astronaut lying in some Martian lawn chair to watch these aurorae," said Nick Schneider, the lead scientist for MAVEN’s instruments at the University of Colorado.

So Mars' atmosphere may be thin and inhospitable, but it makes for one great view.

NASA's MAVEN spacecraft observes Mars' aurora. (NASA)

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