In recent weeks, the Sun has become so noisy that Earth has been repeatedly bombarded with radiation and particles emitted from solar plasma eruptions.
But Earth is not the only planet affected by solar storms. At only 1.5 times Earth’s distance from the Sun, Mars has also been buffeted by the massive ejections of particles shot through the Solar System.
The red planet’s magnetic environment and atmosphere are much weaker than Earth’s, so the effects of solar storms look a little different there. But instruments like those on the MAVEN orbiter have recorded these effects—and now we can use that data to understand the radiation environment on Mars and how it might affect future human explorers.
“This was the largest solar energetic particle event that MAVEN has ever seen,” says physicist Christina Lee of the University of California, Berkeley. “There have been several solar events in recent weeks, so we’ve seen wave after wave of particles hitting Mars.”
Here on Earth, the biggest effects were seen in early May, when eruptions known as coronal mass ejections (CMEs)—huge ejections of solar plasma and magnetic fields that sometimes occur alongside solar flares—were ejected into our direction.
The result was an impressive array of auroral colors seen at latitudes not normally accessible to such views, as solar particles became entangled with Earth’s magnetic field and rained down on Earth’s atmosphere, where interactions with its particles created a stunning light show.
The sunspot region responsible for these flares subsequently rotated to the opposite side of the Sun, but our host star was not done with its deceptions. On May 20, an absolutely massive flare occurred on the far side of the Sun, a flare rated at X12, which would place it among the most powerful solar flares ever detected. Immediately afterward, the CME erupted forward—and Mars was in the firing line.
Light from the eruption arrived first, bathing Mars in solar X-ray and gamma radiation. CME particles travel significantly slower than the speed of light, so they arrive a little later, causing auroras in the Martian atmosphere.
Mars does not have a global magnetic field like Earth. There is no operational internal activity – a dynamo – to produce it. On Earth, the magnetic field accelerates solar particles to the poles, where they fall into the ionosphere. This is why aurora activity is concentrated at higher latitudes.
Since Mars has no magnetic field to do this, the auroras there are usually global. But there is a catch. The resulting “light shows” are in the ultraviolet – meaning we won’t be able to see them with the naked eye.
Fortunately, we have satellites in orbit around the red planet that can. MAVEN captures the ongoing ultraviolet fluctuations in Mars’ atmosphere as wave after wave of solar particles slam into it.
Rovers on the surface are also measuring the radiation flux from the eruption. Earth’s atmosphere blocks the most energetic light from reaching the surface, but the volume of the atmosphere around Mars is less than 1 percent of that of Earth. leaves almost no protection from the sun’s rays.
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After the giant eruption, Curiosity’s radiation assessment detector recorded a radiation surge of up to 8,100 micrograms—the equivalent of 30 chest X-rays at once and the largest surge recorded by the rover. Such a jump wouldn’t be lethal, but it wouldn’t be great for health either.
In fact, Curiosity’s black-and-white images taken during the storm are filled with “snow” — static produced by charged particles interacting with the camera.
The measurement gives scientists working on the Mars mission development a key data point for understanding what type of radiation environment the explorers may be entering, which can help develop strategies to avoid or protect against surges.
“Rocks or lava tubes would provide additional protection for an astronaut from such an event. In Mars orbit or in deep space, the dose rate would be significantly higher,” says physicist Don Hassler of the Southwest Research Institute.
Meanwhile, as we enter the most active phase of the solar cycle, even more storms are predicted. Hassler adds, “I wouldn’t be surprised if this active region of the Sun continues to erupt, meaning even more solar storms on both Earth and Mars in the coming weeks.”
