Last week, when NASA announced it would reveal some major new findings about the Mars atmosphere, we speculated they would indicate that solar winds were responsible for decimating the air, causing it to be about one percent as thick as Earth’s.
At a news briefing today, the space agency confirmed those predictions, concluding that data gathered from the Mars Atmosphere and Volatile EvolutioN Mission (MAVEN) space probe shows how solar winds — traveling at over a million miles per hour — essentially stripped Mars of particles in the upper atmosphere and led to a major loss in ambient gases — most notably oxygen and carbon dioxide.
As a result of a loss in atmosphere, the vast amounts of water that once covered much of the ancient Martian surface — amounts that could have sustained microbial life — no longer existed in a stable environment that allowed it to exist in a liquid form. A thinner atmosphere means much lower pressures and highly unstable temperatures where water would freeze or vaporize almost instantly.
The planet dried up, and the result is an extremely cold and dry red rock.
MAVEN, orbiting Mars since September of last year, was expressly designed to study the planet’s atmospheric processes under the lens of solar winds. NASA scientists have been sitting on plenty of data for months now, but as Bruce Jakosky, the lead scientist for MAVEN, described at today’s news briefing, the type of instruments fitted by the orbiter “require analysis and calibration” that’s quite time-consuming.
Finally though, at the news briefing and in a papers published today in Geophysical Research Letters and Science, the team of researchers illustrate how the atmosphere was essentially blown away — and took the water with it.
Solar winds emitted from the sun basically give gas ions sitting in Mars’ upper atmosphere enough of an energy kick that they are able to escape the planet’s gravitational pull and leak out into outer space. Thick atmospheres, like the one we have here on Earth, are important for giving aqueous environments the kind of stable temperatures and pressures needed to maintain a liquid state and flow freely.
But solar winds also hit every other planet in the solar system — including Earth. Why hasn’t the blue planet lost its atmosphere and water the way the red planet has?
The answer has to do with magnetic fields. Earth has a magnetic field, created by the poles, that keeps solar winds at bay and protects our planet from being beaten down by intense forces of energy.
Mars, on the other, lost its magnetic field a very long time ago, leaving the atmosphere naked to the effects of the sun. When solar winds hit the planet, they do so like a shockwave — creating a conical shape where by the front of the planet is bludgeoned and the upper atmosphere’s ions are completely exposed to energy effects.
Dave Brain, MAVEN co-investigator for the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, Boulder (where Jakosky is also based) explained at the briefing that Martian atmosphere is currently escaping at a rate of about half a pound per second — most of it oxygen and carbon dioxide.
This actually isn’t a tremendously high rate, but when you scale that over a few billion years, that atmosphere (or lack thereof) adds up quickly.
Brain emphasized “this escape rate is a lower limit,” because it doesn’t take into account neutral particles that might be escaping, and also doesn’t currently demonstrate the exponentially bigger particle loss that happens during more volatile solar events.
About 3.1 billion years ago liquid water on Mars seemed very abundant — with vast lakes and oceans inundating the surface. Jakosky and his team theorize the “loss of the atmosphere occurred in that time frame,” between 4.2 to 3.7 billion years ago. The magnetic field most probably disappeared around then, too.
At the current rate of loss, the atmosphere would completely disappear in a couple billion years. But Jakosky cautioned there’s still gas trapped in the rock and underground. “We think [the atmosphere is] being replenished by these non-atmospheric reservoirs.”
Still, he made it clear that there’s no way to reverse the effects and give Mars a brand new atmosphere capable of sustaining the water the planet once did. “It’s not there anymore…[and] it’s not possible to bring it back,” he said. Nowadays, liquid water on Mars only exists in transient states on the surface or potentially in aquifers below the surface.
The new discovery, of course, raises the big question of whether the Earth is on its way to experiencing a similar fate. Brain confirmed that indeed, “today’s Earth is indeed “losing atmospheric particles” but reiterated that our magnetic field protects us — and will continue to do so as long as the Earth’s core stays hot enough to produce a magnetic field. That could certainly change in the distant future, but it’s definitely nothing to worry about for a long time.
The MAVEN team and other scientists hope to learn in more detail how exactly the loss of the Martian atmosphere occurred.
“We’re trying to piece together an overall picture of what happened to Mars with water,” said Jakosky.
But with the vast bulk of that process having already happened over the last few billion years, it’s difficult to empirically study.
Nevertheless, the new findings are an amazing step forward in answering the big mystery about whether there was or currently is life on Mars. And investigating that question requires a comprehensive look at the planet. The atmosphere is just one factor, but it will help inform researchers who are studying other aspects how they should study the planet.