In May 2024, Earth was hit by the biggest solar superstorm recorded in over 20 years, which also hit Mars.
What happens when a solar superstorm hits Mars? Fortunately, ESA’s two Mars Orbiters – Mars Express and ExoMars Trace Gas Orbiter (TGO) – were in the right place at the right time, with a radiation monitor aboard TGO picking up a dose equivalent to 200 ‘normal’ days in just 64 hours.
A new study has now detailed this phenomenal event in more detail, recording how the storm affected Mars’ atmosphere.
“The impact was remarkable: Mars’s upper atmosphere was flooded by electrons,” stated ESA Research Fellow Jacob Parrott, lead author of the study. “It was the biggest response to a solar storm we’ve ever seen at Mars.”
To study Mars’s atmosphere, ESA’s two Mars orbiters make use of a technique called ‘radio occultation’. Credit: European Space Agency
Sudden perils of space weather
The superstorm caused a dramatic increase in electrons in two distinct layers of Mars’s atmosphere at altitudes of around 110 and 130km, with numbers rising by 45% and a whopping 278%.
“The storm also caused computer errors for both orbiters – a typical peril of space weather, as the particles involved are so energetic and hard to predict,” Parrott said.
“Luckily, the spacecraft was designed with this in mind and built with radiation-resistant components and specific systems for detecting and fixing these errors. They recovered fast.”
Using radio occultation to measure impacts of the solar superstorm
To investigate the superstorm’s impact on Mars, Jacob and colleagues used a technique currently being pioneered by ESA known as radio occultation.
Firstly, Mars Express beamed a radio signal to TGO as it was disappearing over the Martian horizon.
As TGO vanished, the radio signal was bent by the various layers of Mars’s atmosphere before being picked up by the orbiter, allowing scientists to glean more about each layer.
Colin Wilson, ESA project scientist for Mars Express and TGO, and co-author of the study, explained: “This technique has actually been used for decades to explore the Solar System, but using signals beamed from a spacecraft to Earth.
“It’s only in the past five years or so that we’ve started using it at Mars between two spacecraft, such as Mars Express and TGO, which usually use those radios to beam data between orbiters and rovers. It’s great to see it in action.”
Understanding how different worlds result in different weather
The solar superstorm was experienced very differently on Earth and Mars, highlighting the differences between the two worlds.
On Earth, the response of the upper atmosphere was more muted, thanks to the shielding effect of Earth’s magnetic field.
As well as deflecting a lot of solar storm particles away from Earth, the magnetic field also diverted some towards Earth’s poles, where they caused the sky to light up with auroras.
While their differences can make it tricky to compare planets directly, understanding space weather forecasting is very important.
On Earth, solar storms can be dangerous and damaging for astronauts and equipment up in space, and can disrupt our satellites and systems (power, radio, navigation) further down.
Overcoming the difficulties of observing space weather
However, studying space weather is difficult because the Sun emits radiation and material erratically, making targeted measurements largely opportunistic.
“Fortunately, we were able to use this new technique with Mars Express and TGO just 10 minutes after a large solar flare hit Mars. Currently, we’re only performing two observations per week at Mars, so the timing was extremely lucky,” Parrott commented.
Together, these events sent fast-moving, energetic, magnetised plasma and X-rays flooding towards Mars. When this barrage of material hit the planet’s upper atmosphere, it collided with neutral atoms and stripped away their electrons, causing the region to fill up with electrons and charged particles.
Wilson concluded: “The results improve our understanding of Mars by revealing how solar storms deposit energy and particles into Mars’s atmosphere.
“This is important as we know the planet has lost both huge amounts of water and most of its atmosphere to space, most likely driven by the continual wind of particles streaming out from the Sun.”