NASA Solar Dynamics Observatory
Mars experienced a sudden rupture in the cosmic order about one year ago. It was almost like the red planet had briefly been transported to another solar system.
Normally in our solar system, the sun is constantly spewing out a stream of charged particles and magnetic fields, called the solar wind.
NASA
This wind washes over the planets and exerts pressure on them that helps hold in their atmospheres. It also interacts with their atmospheres to create aurorae — the colorful northern lights that often appear on Earth.
In December 2022, though, the solar wind suddenly disappeared around Mars, and the planet's atmosphere swelled by thousands of kilometers, as a result.
NASA/JPL
NASA's MAVEN spacecraft, which orbits Mars, observed the whole thing. Scientists announced their discoveries about the event at the fall meeting of the American Geophysical Union, in San Francisco, on Monday.
Scientists determined that the sun had emitted a burst of high-speed solar wind, which swept away a region of the regular solar wind, leaving a void in its wake.
"Each solar storm is different, but this one is extra different," Shannon Curry, principal investigator of the MAVEN mission, said in the briefing.
At Mars, according to MAVEN's data, there was virtually no solar wind — the density of solar particles had dropped by a factor of 100. Mars's atmosphere swelled by thousands of kilometers, as a result.
This unusual type of phenomenon was last seen in 1999, when a NASA satellite observed the solar wind effectively disappear around Earth, causing our own planet's atmosphere to swell five times larger than normal, the NASA scientists said.
NASA/Lacey Young
NASA scientists jumped to study this rare, extreme event for a few reasons.
For one, "solar events are going to be really important to understand for human exploration on Mars," Curry said.
That's because Earth's atmosphere protects us from the sun's shenanigans, but astronauts in space are vulnerable to the extreme radiation that can come with solar eruptions.
NASA plans to send people to Mars one day, which will put them in an extended window of exposure to the solar wind and radiation. The journey would take a total of two to three years, Popular Science has reported. For comparison, NASA astronauts typically only stay on the International Space Station for six months and the longest human spaceflight on record was 437 days.
The vanishing solar wind also offers a clue as to how Mars became such a dry, harsh, lifeless place.
The planet used to be lush with water, and scientists suspect there may have been Martian microbial life at that time. But Mars's atmosphere dwindled away into space, eventually leaving it too cold and exposed for liquid water.
Curry said that powerful barrages of solar wind may have eroded away the Martian atmosphere. To figure out if that's what happened, it helps to study the opposite extreme, when the solar wind vanishes.
There's another alien-life motive to understand the disappearance of the solar wind: The event offers a peek at how rocky planets might look around other, less windy stars.
NASA
The solar wind also interacts with the planet's upper atmosphere to form its magnetosphere — the region of space where Martian magnetic fields dominate.
Just like Earth, the magnetosphere surrounding Mars acts like a bubble that the solar wind must flow around.
But when the solar wind disappeared, the magnetosphere ballooned outward, engulfing the MAVEN spacecraft's full orbit.
As quickly as the solar wind disappeared on December 25, 2022, however, it was back by December 27, 2022, and Mars's atmosphere and magnetosphere shrank back to their regular proportions.
Owen Humphreys/PA Images via Getty Images
The sun is nearing the peak of its 11-year cycle, which means that its bubbling plasma surface is forming more sunspots and emitting more eruptions, floods of solar wind, and other extreme events.
On Earth, we know that solar eruptions and solar storms can create beautiful aurorae, wreak magnetic havoc that messes with compasses, knock satellites out of orbit, and even block radio signals and interfere with power grids.
In the next year, as the sun's activity continues to ramp up to its peak, NASA's MAVEN mission may have even more opportunities to study such solar outbursts from the Martian perspective.
