The first data from NASA’s MAVEN mission to Mars suggest solar bursts enhanced early atmospheric loss. It’s shedding new light on the Red Planet’s cold climate and how it’s changed over billions of years.
It's always the same story with Mars: scientists are desperate to find life there. Every little bit of research leads us that little bit closer to an answer, such as the recent finding of salt-rich water in a crater.
But we're still so far off from knowing the full story about the Red Planet. And that's what makes it so fascinating.
NASA's Maven probe has been orbiting Mars since September 2014. It's been collecting data about the upper atmosphere, ionosphere and magnetosphere.
The first batch of data from Maven has been analysed and the results published across four studies in a special edition of "Science."
And while the main take-home message may at first sound as dry as the Martian climate itself - it is incredibly significant.
Early Martian atmospheric loss
Today, Mars is a very cold and dry planet. We have little reason to consider it a habitable environment.
Scientists believe, however, that one of the keys to the question about life on Mars lies in the level of carbon dioxide (CO2) in its atmosphere. On Earth, CO2 is vital to life.
It's thought early Mars had a very thick CO2 atmosphere. The atmosphere would have to have been thicker than today to support the presence of water. Evidence of flowing water on Mars was revealed in September.
The question is: where did the CO2 go?
There are two options: it either goes down into the crust of the planet where it forms carbon-bearing minerals. Or it rises to the upper atmosphere to be stripped away and lost in space.
Bruce Jakosky, one of the lead researchers working on MAVEN, told "Science," as there was no evidence of carbon-bearing minerals in the crust, it had to be the latter. That's why they have focused on the upper atmosphere - any gases lost to space have to pass through it.
The current escape rate is about 100 grams per second globally, but the rate is variable. It varies depending on the state of the sun, and "it increases dramatically during a solar storm event when a coronal mass ejection hits Mars."
Jakosky and his colleagues studied data collected by MAVEN during an interplanetary coronal mass ejection on March 8, 2015, to gauge the effects of the sun on Mars' atmosphere.
"The variability we're seeing suggests that the escape rate must have been greater in the past when the sun was more active and more intense," says Jakosky. "So we think we're seeing pretty good evidence that loss to space was a significant player in changing the Mars climate."
MAVEN dipper and the magnetic field
In a second paper, Stephen Bougher and colleagues describe how MAVEN "dipped" into the upper atmosphere to gain readings on Mars' thermosphere and ionosphere.
They found higher amounts of oxygen than estimated. They also detected a "steady mixing of carbon dioxide, argon, and nitrogen dioxide."
The density of these elements varied as MAVEN completed each orbit. The scientists say this variability may have been caused by gravity wave interactions with wind and low-level mixing processes.
Other variations determined in the magnetic field and ion layers suggest the crust of Mars may contribute to Mars' weak and scattered magnetic field.
To the northern lights
MAVEN has also collected data on a newly discovered aurora in Mars' northern hemisphere.
The probe spotted the aurora during a solar energetic particle burst, using an Imaging Ultraviolet Spectrograph to render UV light.
Nick Schneider and his colleagues say the Martian aurora is similar to Earth's Northern Lights - with an exception.
The Northern Lights are tied to the magnetism of the Earth's poles, whereas Mars' aurora may be tied to the "remnant magnetic field of the crust."
The fourth paper by Laila Andersson and colleagues handles the discovery of dust particles at orbital altitudes of about 150 to 300 kilometers.
It's not known where the dust originates, but the authors believe it is interplanetary.
Getting to the bottom of this question may explain a fundamental process in the Martian atmosphere.
Together with the work being done by the Curiosity and Opportunity rovers on the ground, the scientists hope to forge ahead with new Martian discoveries over the next year and beyond.
"We have a science team that is about 125 people, and everybody is just beside themselves with the quality of the data and the results we’re getting," says Jakosky.
MAVEN has enough fuel for about a decade, which means there is the potential to study a full solar cycle and see what impact that has on Mars.
For now, though, MAVEN's mission has been extended for just another year. But given that one Martian year is two on Earth, the scientists have only just seen half the story so far.