In recent weeks, the Sun has become so noisy that the Earth has been repeatedly bombarded with radiation and particles emitted by solar plasma eruptions.
But Earth is not the only planet affected by solar storms. Mars, at a distance of only 1.5 times Earth’s distance from the Sun, was also hit by huge bursts of particles ejected from 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 registered 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 event of solar energetic particles that MAVEN has ever seen,” says physicist Christina Lee of the University of California, Berkeley. “There have been several solar events in the past few 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 outbursts of solar plasma and magnetic fields that sometimes coincide with solar flares—were spewed our way.
The result was a spectacular array of aurora colors, seen at latitudes not normally privy to such objects, as solar particles became entangled in Earth’s magnetic field and rained down into Earth’s atmosphere, where interactions with its particles created a stunning light show.
The sunspot region responsible for these eruptions subsequently turned away from the Sun, but our host star wasn’t done with its mirages. On May 20, there was an absolutely massive eruption on the far side of the Sun, estimated at X12, which would make it one of the most powerful solar flares ever recorded. A CME erupted immediately afterwards – and Mars was in the firing line.
Light from the eruption arrived first, flooding Mars with solar X- and gamma rays. CME particles travel significantly slower than the speed of light, so they arrived a bit later and triggered the auroras in the Martian atmosphere.
Mars does not have a global magnetic field like Earth. It does not have the operational internal workings – the dynamo – to produce it. On Earth, the magnetic field accelerates solar particles to the poles, where they rain down into the ionosphere. Therefore, aurora activity is concentrated in higher latitudes.
Because Mars doesn’t have a magnetic field to do this, auroras tend to be global there. But there is a catch. The resulting “light shows” are in ultraviolet light – meaning we wouldn’t be able to see them with the naked eye.
Fortunately, we have satellites orbiting the red planet that can. MAVEN captures the ongoing ultraviolet fluctuations in the Martian atmosphere as wave after wave of solar particles slam into it.
Rovers on the surface also measured the influx of radiation from the eruption. Earth’s atmosphere blocks the most energetic light from reaching the surface, but the volume of the atmosphere surrounding Mars is less than 1 percent of Earth’s. they leave almost no protection from the sun’s rays.
frameborder=”0″ allow=”accelerometer; automatic playback; clipboard-write; encrypted media; gyroscope; picture in picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>
After the giant eruption, Curiosity’s Radiation Assessment Detector recorded a radiation increase of up to 8,100 micrograys — the equivalent of 30 chest X-rays at once and the largest increase recorded by the rover. Such an onslaught wouldn’t be fatal, but it wouldn’t exactly be great for one’s health.
Curiosity’s black-and-white images taken during the storm are actually filled with “snow” — static electricity produced by charged particles interacting with the camera.
The measurement gives scientists working on Mars mission development a key data point for understanding what kind of radiation environment the explorers might be entering, which can help design strategies to avoid or protect against surges.
“Cliffs or lava tubes would provide additional shielding 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, even more storms are forecast as we enter the most active phase of the solar cycle. Hassler adds, “I wouldn’t be surprised if this active region on the Sun continues to erupt, meaning even more solar storms on Earth and Mars in the coming weeks.”