Every weekday, Kerry Lee and his team watch the sun. At 8:30 in the morning, Houston time, one of seven space environment officers takes their place in front of a bank of computer screens in a back room of NASA’s Johnson Space Center. From there, they keep track of the sun’s moods: angry eruptions, stewing sunspots, stretches of calm and quiet.
They’re watching for one kind of solar tantrum in particular: eruptions that send high-energy particles hurtling toward Earth and its neighbors. Their charges include the crewmembers aboard the International Space Station, who could face health risks from this kind of radiation, depending on where they and the station are when the outburst comes.
“Most of the time, we’re calming people down as opposed to alerting them,” says Lee, who leads the operations team for NASA’s Space Radiation Analysis Group. When the sun is quiet, and when no one is on a spacewalk, the solar sentries are on duty four hours a day.
But their job is poised to become much more time-consuming. As NASA prepares to send astronauts back to the moon for the first time since 1972, Lee and his fellow officers are preparing for the extra radiation risks these space travelers will encounter. During the crewed Artemis missions, they’ll be “on console” 24 hours a day.
They will be on duty because particle storms stand to wreak far more havoc on missions that leave the umbrella of Earth’s magnetic field. As humans prepare to make their way deeper into space in the coming decades, scientists are hard at work on the tricky task of predicting solar weather.
“This is a significant challenge,” says Rami Qahwaji, a computer scientist who studies space weather forecasting at the University of Bradford in the U.K. “In order to protect future generations of human explorers, we need to get this right.”
Humans have been keeping an eye on the sun for a long time. Records of sunspots, the blotches that periodically speckle the solar surface, date back centuries, Qahwaji says. But compare that time to the 4.6 billion-year life of the sun: “It’s like me trying to understand everything about you just by spending two seconds with you.”
One thing we do know, he says, is that the sun’s temperament largely follows an 11-year cycle, moving from quiet to active and back again. More sunspots dot the surface at the peak of the cycle, according to the Space Weather Prediction Center of the National Oceanic and Atmospheric Administration.
These spots, with their roiling and reconnecting magnetic fields, are often the location of solar eruptions: blasts of electromagnetic radiation in the form of solar flares and belches of plasma known as coronal mass ejections. When they reach Earth, coronal mass ejections can mess with the planet’s magnetic field, in some cases making the power grid and navigation systems go haywire. Large solar flares, meanwhile, can cause blackouts in high-frequency radio communication.
The waves of radiation that Lee’s team worries about are rarer, but when they do happen, they often come alongside these eruptions. Charged particles like protons get swept up and careen toward Earth and its orbiting astronauts. This kind of radiation is known to cause acute sickness in people who are exposed to a lot of it all at once — though modeling studies have shown that spacecraft shielding goes a long way toward preventing vomiting, skin rash and other symptoms. But even lower doses over a long period of time can raise the risk of cancer and other illnesses by damaging DNA. The goal of the space environment officers, Lee says, is to keep astronauts’ exposures as low as possible while they carry out their missions.
Most of the time, the astronauts aboard the International Space Station are protected from onslaughts of particles by Earth’s magnetic field. When the space station is within that protective region and the astronauts are inside, Lee says, “the sun can do whatever it wants.” Still, his team is on duty whenever an astronaut leaves the shelter of the station or a particle storm passes through.
The space environment officer on duty can make a few recommendations to the mission’s flight surgeon if the space station crew risks being exposed. This could be the case if a particle storm happens while the station is traveling near Earth’s magnetic poles, where shielding is feebler. The officer might advise that astronauts stay away from parts of the station with thinner walls, like the connector between the U.S. and Russian sections.
On rare occasions, an officer might recommend that crew members actively shelter in the most heavily shielded parts of the station; Lee says the U.S. lab and the polyethylene-padded U.S. crew quarters offer extra protection. To his knowledge, this has happened only twice in the space station’s history, both before he became an officer.
That’s the “luxury” of low-Earth orbit, Lee says: “It takes a relatively extreme event at the right time” to warrant that kind of action. “When we go to the moon, we’re not going to have a geomagnetic field,” he says. “We’re going to be exposed to the solar energetic particles at all times” whenever a storm is happening.
For missions deeper into space, he says, one contingency plan is to cobble together a radiation shelter using materials onboard. In this scenario, passengers would yank equipment out from hollow bays beneath their seats, climb down into those bays, and pull the equipment over the openings — hiding themselves away in makeshift dens that are shielded in all directions.
The space environment officers make these recommendations from their mission control room in Houston. The battery of screens projects all manner of data, including portraits of the sun filtered to display different wavelength ranges, like x-rays or ultraviolet. At least once a day — more, if the sun is acting up — Lee’s team is on the phone with someone at NOAA’s Space Weather Prediction Center.
“Just like a regular weather station, we issue alerts and warnings,” says William Murtagh, the center’s program coordinator. “Except we don’t care about hurricanes or blizzards or droughts. Our interests lie in space.”
To protect spacefarers, it helps to know in advance what the weather will be — and Lee’s team works with NOAA to anticipate events as much as possible. At the moment, however, it’s harder to forecast bursts of solar particles than garden-variety thunderstorms. Efforts to model them are still in their “infancy” compared to Earth-based weather, Murtagh says. One of the biggest challenges is the dearth of real-time data from space; the observational network up there is much sparser than the fleet of weather stations and balloons here on Earth.
It doesn’t help that the processes involved in producing a solar particle storm are fiendishly complex.
“It’s this massive system starting at the sun, all the way to wherever you are, with all of these different physical phenomena in the chain,” says Kathryn Whitman, who studies these modeling efforts as part of the Space Radiation Analysis Group. Whether the particles reach you depends on what kind of eruption happens on the sun, but also where that eruption occurs and what else the particles encounter on their journey toward Earth.
“The forecasting of solar particle events is one of the most challenging things in space weather,” says Juha-Pekka Luntama, head of the European Space Agency’s Space Weather Office. “I would call it the holy grail.”
Luntama isn’t extremely worried about traveling to the moon, as long as missions can wait for a tranquil sun. He says that, with current capabilities, scientists can forecast reasonably well that a strong solar particle event is unlikely to happen within the next couple of days. The flight can launch when there are no angry-looking sunspots, and travelers can build a radiation shelter on the lunar surface once the spacecraft lands.
But there is still room for improvement when it comes to forecasting for a short flight to the moon, Luntama says. And the trip to Mars will be much longer — too long to give a reliable all-clear prediction — so it poses a greater challenge. “I think we still have work to do before we are ready for that,” he says.
As for solar particle events, there are a host of models currently in use or being developed. They range from well-tested to brand-new and rely on different approaches to make their predictions.
Several are based on historical statistics: They look at what happened during past particle storms — how strong was the flare? How fast was the coronal mass ejection? — and predict storms according to how the sun is acting now. These kinds of models are nimble and work well for real-time predictions, write the authors of a recent review led by Whitman. But because the more dangerous, high-energy outbursts are rare, statistical models have a harder time capturing those events.
Other models try to replicate the physics of the sun to catch storms brewing, but these are unwieldy, requiring a lot of time and computing power. Still others leverage machine learning to predict solar particle events, as Qahwaji’s system does for flares; they’re similar to the statistical models, with the hope that a computer will discover a pattern humans have missed.
The problem, the authors write, is that only a fraction of these models provide real-time predictions, in part because space-based observations are so meager. Plus, it’s not always clear how well they’re doing — though scientists are working to put them to the test. Validation efforts, like a “scoreboard” developed in part by the Space Radiation Analysis Group, compare how several models-in-the-making are performing.
In the meantime, Lee’s team is in preparation mode. From the Nov. 16 launch of Artemis I until splashdown 25 days later, the space environment officers ran what Lee called a “practice go.” Twenty-four hours a day, seven days a week, an officer was on duty.
While there were no astronauts onboard, the first Artemis mission did carry an instrument that measured the space radiation environment and beamed data back to Lee’s team in Houston. The sun was pretty quiet during the mission. But Lee says the practice run was useful, because it allowed the officers to make sure the onboard measurements matched their models.
Ultimately, he says, forecasting is challenging — but that shouldn’t stop explorers from venturing into deep space.
After all, humans landed on the moon more than half a century ago. “We’re much further along now than we were then. Do you ever have every tool that you want with you when you’re embarking on something unknown? The answer’s no,” he says. “But we accept the risk, and we believe that it’s worth it.”
And when NASA sends humanity back to the moon for the first time in decades, the solar sentinels will be watching.