Solar superstorm gave ESA's Mars orbiters a handy science opportunity

Veteran spacecraft overcome computer glitches as atmosphere 'flooded by electrons'

Almost two years ago, a solar storm hit Earth, triggering auroras that were seen as far south as Mexico. The storm also reached Mars and was detected by a pair of ESA spacecraft, Mars Express and ExoMars Trace Gas Orbiter (TGO).

The storm caused computer errors on both spacecraft – "a typical peril of space weather, as the particles involved are so energetic and hard to predict," said ESA Research Fellow Jacob Parrott. "Luckily, the spacecraft were designed with this in mind, and built with radiation-resistant components and specific systems for detecting and fixing these errors. They recovered fast."

However, the storm also presented opportunities, and using radio occultation, scientists were able to investigate its impact on Mars.

Mars Express beamed a radio signal to TGO just as the latter was vanishing over the Martian horizon. As TGO vanished, the radio signal was refracted by the layers of Mars's atmosphere, allowing scientists to gather data on each layer.

"The superstorm caused a dramatic increase in electrons in two distinct layers of Mars's atmosphere at altitudes of around 110 and 130 km, with numbers rising by 45 percent and a whopping 278 percent, respectively," Parrott said. "This is the most electrons we've ever seen in this layer of Martian atmosphere."

Colin Wilson, ESA project scientist for Mars Express and TGO, and co-author of the study published in Nature Communications, said: "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."

The researchers also credited observations from NASA's MAVEN mission to confirm the electron densities. The fate of MAVEN is unclear since the spacecraft has not been heard from since December 6. On March 4, NASA announced that a review board was evaluating recovery efforts for the spacecraft and assessing the probable state of the vehicle.

The two spacecraft are past their primary missions but remain capable of producing valuable science. Mars Express was launched in June 2003 and is now into its third decade of operations. A software update in 2025 meant that controllers could operate the spacecraft while leaving the gyros used for pointing the spacecraft – which are wearing out – deactivated most of the time. A source at ESA explained: "We can run the wheel offloadings now with the gyros fully off thanks to a typically MEX hand-compiled software patch directly to the star tracker RAM."

The change means there is every chance that, from a hardware perspective, Mars Express could endure into the 2030s, and support Japan's Martian Moons Exploration (MMX) mission, which is due for launch in 2026. Such an extension would, however, require a budgetary nod from ESA, which won't come until later this year. ®