NASA Releases a Year's Worth of Data About the Habitability of Mars
MAVEN gathers data on Mars's atmosphere that could reveal more habitable times on the Red Planet.
Artist's impression of MAVEN. Image: NASA/Goddard Space Flight Center
Was Mars once habitable? That's the million-dollar question probed further by a NASA announcement on Thursday of important new findings from its MAVEN orbiter.
MAVEN, full name the Mars Atmosphere and Volatile Evolution Mission, started orbiting Mars just over a year ago with the goal of gathering data about the Martian atmosphere. Researchers are looking for evidence of how Mars's climate has changed over time—in particular, how the planet has lost so much of its atmosphere, and with it so much of the water we believe used to be there.
Thursday saw the release of almost 50 new research papers from the MAVEN mission, published in the journals Science and Geophysical Research Letters, all of which add to the data about Mars's atmosphere and what that might tell us about the evolution of its climate.
In an introductory paper led by Bruce Jakosky at the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder, the authors explain MAVEN is "the first spacecraft devoted to studying the Mars upper atmosphere and ionosphere, its interactions with the Sun and the solar wind, and the consequent escape of atmospheric gases to space."
Stephen Bougher, a co-investigator on the MAVEN mission and a research professor at the University of Michigan, characterised the orbiter as a natural counterpart to observations of water on the Martian surface, which recently led to the strongest evidence yet of flowing (albeit salty) water on Mars.
Water, naturally, is a key indicator of habitability, which is why so many space missions set out to look for it.
"MAVEN is the other half of the story, where we're looking at where the water might have gone if it escaped the top of the atmosphere," he said in a phone interview.
Bougher was restrained in speculating on the potential for life on Mars, but said that the MAVEN mission followed NASA's general "follow the water" strategy. "If you know how much water would have been lost over time then you have some idea of how thick the atmosphere would have been, and that ups the chances that life, if it did form, could have formed," he said.
"Obviously we haven't discovered it yet, any extant or existing life, but we're looking," he added.
Bougher summarised the mission as "trying to find out how Mars turned out to be quite a bit different than the Earth has come to be."
The atmosphere on Mars is cold, dry, and thin. It's less than one percent that of Earth, hence the cold temperatures and lack of protection against radiation from the Sun. But research suggests it wasn't always that way, and that the Red Planet could once have more closely resembled our Blue Planet.
Mars is more vulnerable to gas escaping from its atmosphere because it doesn't have a strong magnetic field like Earth to protect it from solar winds and has less gravity owing to its smaller size—"so it's a lot easier to escape species from the atmosphere than it is from Earth," explained Bougher, "species" here referring to types of gases and ions.
With the current set of papers, the researchers are looking at how these are lost from Mars's atmosphere today in order to then "extrapolate back in time" to find out what it could have been like in the past.
How did the climate of Mars change over time and how did the loss of water change over time on Mars?
One paper led by Jakosky found a dramatic increase in ions escaping the Mars atmosphere during a solar storm, or interplanetary coronal mass ejection (ICME). The researchers took measurements during a solar event on March 8 this year and found that ion loss was increased by about an order of magnitude.
As it's thought that these solar events were more prevalent earlier on in the Solar System, they write that "the inferred climate change on Mars may have been driven to a large extent by these solar storms."
Another paper, led by Bougher, characterises the structure and variability of Mars's upper atmosphere, and Bougher said there were some surprises. For instance, they found that temperatures varied more from orbit to orbit than you would expect based on ultraviolet radiation, which is thought to largely control temperatures at that level.
"This large orbit-to-orbit variability implies that dayside thermospheric temperatures are not controlled exclusively by solar EUV forcing, as models might predict," the authors write.
"It means there's variability that can happen over time at Mars that we didn't expect," said Bougher. The paper suggests this variability could be driven by gravity waves.
Other papers look at interplanetary dust in Mars's atmosphere, planetary auroras, and a host of other features that all feed into this understanding of what Mars's atmosphere is like now, and what it was like in the past.
Bougher said the next step is to incorporate all the new data into models for Mars's atmosphere loss, validate them by reproducing results consistent with present-day measurements, then effectively take them back in time to track the changes in atmosphere, climate, and ultimately water. "That's what we're looking for here: How did the climate of Mars change over time, how did the loss of water change over time on Mars?" he said.
MAVEN has only been up there for half a Mars year (one Earth year) so the team will keep gathering data and keeping an eye out for more unpredictable opportunities for study such as dust storms and solar storms.
Bougher said he had been looking forward to a mission like MAVEN for his whole career, and that MAVEN was the first to quantify the "escape rates" of Mars's atmosphere.
"I tell my students, if our models are anywhere close to the reality of the atmosphere, I would be tickled," he said. "Often they're not, and if they're not you're going to learn something—so either way it's a win situation."