In recent weeks, the sun has become so noisy that Earth has been repeatedly bombarded with radiation and particles emitted by bursts of solar plasma.
But Earth isn’t the only planet affected by solar storms. At just 1.5 times Earth’s distance from the Sun, Mars is also being buffeted by the massive outpourings of particles emitted 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 recorded those effects — and now we can use that data to understand the radiation environment on Mars, and how it could affect future human explorers.
“This was the largest solar energetic particle event 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 saw wave after wave of particles hitting Mars.”
Here on Earth, the biggest impacts were seen in early May, when eruptions known as coronal mass ejections (CMEs) – huge bursts of solar plasma and magnetic fields that sometimes occur along with solar flares – were spewed in our direction.
The result was a spectacular array of polar colors seen at latitudes where such sights are not normally seen, as solar particles became entangled in Earth’s magnetic field and rained down into Earth’s atmosphere, where interactions with the particles created a stunning produced a light show.
The sunspot region responsible for these outbursts then turned away to the far side of the Sun, but our host star wasn’t done with its tricks yet. On May 20, an absolutely massive eruption occurred on the far side of the Sun, an eruption estimated at X12, which would make it one of the most powerful solar flares ever detected. Immediately afterwards, a CME spewed out – and Mars was in the line of fire.
The light from the solar flare arrived first, flooding Mars with X- and gamma-rays from the Sun. The CME particles travel significantly slower than the speed of light, so they arrived slightly later, creating auroras in the Martian atmosphere.
Now Mars does not have a global magnetic field like Earth. It does not have the operational internal activity – a dynamo – to produce it. On Earth, the magnetic field accelerates solar particles toward the poles, where they rain toward the ionosphere. That is why aurora activity is concentrated at higher latitudes.
Because Mars doesn’t have a magnetic field that can do this, auroras there tend to be global. But there’s a catch. The resulting ‘light shows’ are in ultraviolet, meaning we wouldn’t be able to see them with the naked eye.
Fortunately, we have satellites orbiting the red planet that can do that. MAVEN has captured the constant ultraviolet fluctuations in Mars’ atmosphere as wave after wave of solar particles crash into it.
Rovers on the surface also measured the influx of radiation from the eruption. Earth’s atmosphere blocks most energetic light from reaching the surface, but the volume of the atmosphere around Mars is less than 1 percent of Earth’s volume. which means there is virtually no protection against the sun’s rays.
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After the massive eruption, Curiosity’s Radiation Assessment Detector recorded a radiation wave of up to 8,100 microgray – the equivalent of 30 chest X-rays at once and the largest wave recorded by the rover. Such a wave wouldn’t be fatal, but it wouldn’t be particularly good for health either.
In fact, Curiosity’s black-and-white images taken during the storm are filled with “snow”: static electricity produced by charged particles interacting with the camera.
The measurement gives scientists working on developing the Mars mission an important data point for understanding what kind of radiation environment explorers might enter, which could help design strategies to avoid or be protected from spikes.
‘Cliffs or lava tubes would provide an astronaut with additional protection against such an event. In orbit around Mars or in deep space, the dose rate would be significantly higher,” said physicist Don Hassler of the Southwest Research Institute.
Meanwhile, as we enter the most active phase of the solar cycle, even more storms are forecast. Hassler added, “I wouldn’t be surprised if this active region on the Sun continues to erupt, meaning even more solar storms on both Earth and Mars in the coming weeks.”