Beyond the Northern Lights: How Solar Flares Spread Across the Solar System

The sun is currently extremely active, seeding the biggest solar storms on Earth in 20 years. Here’s what it’s doing to the rest of the solar system.

If you happened to be looking up at the sky a few nights in May 2024, chances were you saw something spectacular. For those at relatively low latitudes, it was a rare chance to see the flickering red, pink, and green glow of our planet’s aurora borealis.

A powerful solar storm had sent blasts of charged particles hurtling toward Earth, and as they bounced around in our planet’s atmosphere, they unleashed spectacular displays of the northern and southern lights. The dazzling displays of the aurora borealis were visible much further south than they would normally be – and much further north in the case of the aurora australis, thanks to the power of the geomagnetic storm, the strongest in two decades.

But while this spike in solar activity left many on Earth mesmerized by the light show it produced, it has had a profound effect elsewhere in the solar system. While most of us have marveled at the colors dancing across the night sky, astronomers have looked far beyond it to see the strange ways such intense bursts of particles affect other planets and the space between them.

“The sun can shoot material out in any direction, like a garden sprinkler,” says Jim Wild, a professor of space physics at Lancaster University in the United Kingdom. “The effects are felt all over the solar system.”

Our sun is heading towards, or has already reached, its solar maximum – the point in an 11-year cycle when it is most active. This means the sun is producing more flashes of radiation and particles from solar flares and events known as coronal mass ejections (CMEs). If these are sprayed in our direction, they can supercharge Earth’s magnetic field, creating magnificent aurorae but also causing problems for satellites and electricity grids.

“It does seem like things are really improving now,” said Mathew Owens, a space physicist at the University of Reading in the U.K. “I think we’re pretty much at solar maximum now, so we could see more of these storms in the next few years.”

Several spacecraft around the sun are observing this increase in activity up close. One of them, the European Space Agency’s (ESA) Solar Orbiter, has been studying the sun since 2020 in an orbit that brings it within the path of Mercury. Currently, the spacecraft is “on the other side of the sun as seen from Earth,” says Daniel Müller, project scientist for the Solar Orbiter mission at Esa in the Netherlands. “So we see everything that the Earth doesn’t see.”

The storm that hit Earth in May was sparked by an active region of solar flares and sunspots, bursts of plasma and spinning magnetic fields on the sun’s surface known as the photosphere. Solar Orbiter was able to see “several of the flares from this monstrous active region that had spun out of Earth’s view,” Müller says, bright flashes of light and darkened areas called sunspots on the sun’s surface.

One of Solar Orbiter’s goals is “to connect what’s happening on the sun with what’s happening in the heliosphere,” Müller says. The heliosphere is a vast bubble of plasma that envelops the sun and the solar system’s planets as it travels through interstellar space. Müller and his colleagues hope to learn more about where the solar wind — the constant stream of particles streaming from the sun across the solar system — “is blowing into the interstellar medium,” he says. “So we’re particularly interested in anything that’s energetic on the sun that we can find in the turbulence of the solar wind.”

This particular cycle, cycle 25, appears to be “significantly more active than people predicted,” says Muller, with the relative number of sunspots – an index used to measure activity across the visible surface of the sun – that exceeds the peak of the previous solar cycle. “We predicted a maximum number of sunspots of 120 [a day]”, Mueller said. “We had a high of 270 last month.”

The effects of these changes in solar activity extend far across the solar system, however. Earth is not the only planet affected by solar storms as they sweep through interplanetary space. Mercury, the closest planet to the sun, has a much weaker magnetic field than Earth—about 100 times weaker—and lacks a substantial atmosphere. But solar activity can cause the planet’s surface to glowing with x-rays while the solar wind is raining down. Venus also has no substantial magnetic field, but the planet still creates auroras while the solar wind is interacts with the planet’s ionosphere.

On Mars the effect of solar activity is more pronounced. Here is a Nasa spacecraft called Connoisseur (Mars Atmosphere and Volatile Evolution) has been studying the planet’s atmosphere from orbit since 2014. “We were on the declining side of solar cycle 24 [then]”, said Shannon Curry, a planetary scientist at the University of Colorado, Boulder in the US and the leader of the mission. “We are now approaching the peak of Cycle 25, and this latest wave of active regions has produced the strongest activity that Maven has ever seen.”

Between May 14 and 20, the spacecraft discovered exceptionally strong solar activity Reaching Mars, including a X8.7 – solar flares are ranked B, C, M and X in order from weakest to strongest. Results from the event have yet to be studied, but Curry noted that an earlier X8.2 burst had resulted in “a dozen papers” published in scientific journals. Another burst on May 20, later estimated to be an even larger X12, hurled X-rays and gamma-rays toward Mars before a subsequent coronal mass ejection launched a barrage of charged particles in the same direction.

Images sent back by NASA’s Curiosity rover on Mars just revealed a lot of energy hitting the Martian surface. Streaks and dots caused by charged particles hitting the camera’s sensors caused the images to “dancing with snow“, according to a NASA press release. Meanwhile, Maven captured glowing aurora as the particles hit the Martian atmosphere, bathing the entire planet in an ultraviolet glow.

The flares can cause the temperature of the Martian atmosphere to “increase dramatically,” Curry says. “In the upper atmosphere, the temperature can actually double. The atmosphere itself swells. The entire atmosphere expands tens of kilometers — exciting for scientists, but harmful for spacecraft, because as the atmosphere expands, there’s more drag on the spacecraft.”

The expanding atmosphere could also cause degradation of the solar panels on spacecraft orbiting Mars. increase in radiation“The last two eruptions have caused more damage than normally occurs in a third of a year,” Curry said.

While Mars has lost most of its magnetic field, it still has “crustacean remnants of magnetic fields, little bubbles all over the southern hemisphere,” Curry says. During a solar event, charged particles can light up and excite the particles. “The entire day side lights up in what we call a diffuse aurora,” Curry says. “The whole sky glows. That would probably be visible to astronauts on the surface.”

By the time solar storms move further out into the solar system, they have usually dissipated, but they can still affect the planets they encounter. Jupiter, Saturn, Uranus and Neptune all have aurorae which are partly driven by charged particles from the sun interacting with their magnetic fields.

But one of the most important effects of solar activity on interplanetary space that astronomers are eager to study is something that ‘slow solar wind“, a slower but denser stream of charged particles and plasma from the sun. Steph Yardley, a solar astronomer at Northumbria University in the United Kingdom, says solar wind is “generally classed as being around 500 km/s (310 miles/s),” but slow wind falls below that. It also has a lower temperature and is generally more volatile.

Recent work by Yardley and her colleagues, using data from Solar Orbiter, suggests that the Sun’s atmosphere, its corona, plays a role in the speed of the solar wind. Regions where the magnetic field lines, field direction, and charged particles are “open”—extending out into space without looping back—provide a highway for solar wind to reach high speeds. Closed loops above some active regions—where the magnetic field lines have no beginning or end—can occasionally snap, producing a slow solar wind. The variability in the slow solar wind appears to be driven by the unpredictable plasma flow in the suncausing the magnetic field to become extremely chaotic.

The X-class flares and coronal mass ejections seen in May transformed the interplanetary medium as they hurled material through the solar system. Solar Orbiter a huge peak in ions detected that are moving at thousands of kilometers per second immediately after the May 20 flare. Computers aboard other spacecraft – the BepiColombo Studywho is currently on a seven-year journey to Mercury, and Mars Expressorbiting the Red Planet – both saw a dramatic increase in the number of memory errors caused by the high-energy solar particles hitting the memory cells.

Increased solar activity is a boon for scientists. “If you keep track of the number of papers that solar physicists write, you can almost see an 11-year cycle,” Owens says. “We’re all more scientifically productive when there’s a lot of activity to study.”

As the sun continues its solar maximum, the solar system will see more and more activity streaming from its surface. But while all planets witness at least some of the activity, our planet bears the brunt of the burden more than most. “Earth is somewhat unique in that space weather can have interesting effects on human technologies,” Wild says. “There’s an extra dimension here on Earth.”

Perhaps someday those anthropogenic effects will be felt elsewhere. “If you’re going to fly to Mars and you’re going to have a six-month flight through the interplanetary environment, you’re going to potentially soak up a lot of space weather events,” Wild says. “How you protect your astronauts is an interplanetary problem that we have to get our heads around.”

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