Key Insights
This September, the US launched three new missions into space, all of which are designed to monitor the impacts of space weather.
Space weather arises from solar flares and coronal mass ejections.
These solar phenomena pose a risk to ground- and space-based infrastructure and astronauts, so understanding and predicting such events is vitally important.
In August 1972, off the coast of Vietnam, dozens of naval mines exploded simultaneously. To the US Air Force pilots flying overhead, the explosions seemed spontaneous; no ship was near enough to flip the mines’ magnetic triggers. Ultimately, the US Navy attributed the detonations to a source nearly 150 million km away: a solar flare and its accompanying coronal mass ejection (CME).
Dubbed the seahorse flare based on its swirling, marine-creature-esque appearance, it was the first space-age solar event that would have exposed any astronauts in space to extraordinary levels of radiation. Luckily, the crew of Apollo 17 were safely on the ground preparing for their December takeoff.
A powerful flare was captured in August 1972 by the Big Bear Solar Observatory in California. It was called the seahorse flare after the shape of its brightest regions. Since then, the optics used for solar telescopes have improved greatly.
Credit:
NASA
As the US makes plans to send astronauts back to the moon, space technology expands, and more of the earthbound population relies on satellites for basic needs, it has become vitally important to understand and predict the hazards hurled at Earth from our nearest star. In a press conference on Sept. 21, Nicky Fox, the associate administrator of NASA’s Science Mission Directorate, pointed to the seahorse flare as a reminder of the power of space weather.
That’s why NASA and the US National Oceanic and Atmospheric Administration launched three new space-weather missions on Sept. 24: the Interstellar Mapping and Acceleration Probe (IMAP), Carruthers Geocorona Observatory, and the Space Weather Follow On–Lagrange 1 (SWFO-L1).
“This is the ultimate cosmic carpool,” said Joseph Westlake, director of NASA’s heliophysics division, during a second press conference, about the science goals of the missions.
But what are solar flares and CMEs? And can scientists predict when they’ll hit?
How the sun causes space weather
“It’s all about magnetic fields on the sun,” says solar astrophysicist Maria Kazachenko, a professor at the University of Colorado Boulder and the US National Solar Observatory. “Here on Earth, we care about gravity. We throw anything and it just falls down. On the sun, everything follows the magnetic field loops.”
Video images captured by scientists using advanced solar optics at the Goode Solar Telescope at Big Bear Solar Observatory in California show how plasma follows magnetic fields on the sun, either as it rains back to the solar surface (left) or twists and dances up from it (right).
Credit: Schmidt et al./NJIT/NSO/AURA/NSF
The sun’s magnetic field likely arises from the roiling plasma that forms the star. The unique state of matter is made up of ionized gases and their freed electrons. Because the charged particles are moving, they create magnetic fields; the plasma both carries and creates the magnetic fields in the solar atmosphere, Kazachenko says.
Particularly active regions can arise on the solar surface when magnetic energy bubbles up from within the star. And as different parts of plasma move on the solar surface, the associated magnetic fields become taught and tangled. “When these magnetic field lines become too tangled, they can snap,” explains Madhulika “Lika” Guhathakurta, an astrophysicist who helped build and lead NASA’s Living with a Star initiative. “Think of it like stretching a rubber band until it breaks.”
Once they’re broken, those magnetic lines rapidly rearrange in a process called magnetic reconnection. The process releases a tremendous amount of energy and triggers a solar flare.
“This is like a cosmic short circuit, releasing all its energy at once. It’s instantaneous,” Guhathakurta says. The result is an explosion of photons that have energies across the electromagnetic spectrum, from radio waves to gamma rays, that sends radiation throughout the solar system before slowly fading away, she says.
The massive release of energy also acts as a particle accelerator. And if the flare is pointed toward Earth, our planet is bombarded not only with electromagnetic radiation but also a shower of protons, electrons, and ions from the sun.
But solar flares are only one part of space weather. If enough energy is released through magnetic reconnection, a portion of the solar corona—the outermost part of the sun’s atmosphere—can explode into space as a CME.
“The outermost, fastest layer that’s pushing particles ahead of it, pushing through space, arrives here at Earth with a punch,” says Shawn Dahl, a space weather forecaster at NOAA’s Space Weather Prediction Center. When the shock front slams into Earth’s magnetic field, it pushes the field around, which “immediately spins up [magnetic] activity,” he says.
Space weather comes from the sun
The sun is responsible for the space weather experienced by every living thing on Earth. Although a solar wind of charged particles constantly blows out from the sun, sometimes the star is even more active as areas of its magnetic field become strained and tangled. These areas are often marked by sunspots—visibly dark regions on the sun’s surface. Ultimately, the tangled magnetic fields can snap and release energy in the form of a solar flare, coronal mass ejection, or both. When one of these solar events is directed at Earth, the associated charged particles and magnetic field interact with the planet’s magnetic field. Large flares can disrupt communications, and large coronal mass ejections can cause power-grid blackouts and spectacular displays of aurora.
A graphic shows half of an orange sun on the left and the entire planet Earth on the right. The sun has sunspots on its surface, a solar flare in the form of a white star shape, and a coronal mass ejection drawn a loop of orange coming off the surface. The solar wind is indicated with dashed orange lines pointing toward Earth. The planet’s magnetic field is shown.
Credit:
Yang H. Ku/C&EN
Then, the bulk of the CME arrives, carrying its own magnetic field. “We get really concerned about the orientation of that magnetic field in space,” Dahl says. Its strength and orientation in relation to Earth’s magnetic field determines the intensity of the resulting geomagnetic storm.
Those storms have a scale. A G1 event is the most minor but may still cause very weak, easily managed power fluctuations on some power grids. In contrast, a G5 event can cause power grids to fail, make radio navigation impossible, interfere with satellite functions, and send auroral displays down to midlatitudes. Or, as back in the 1970s, possibly trigger naval mines to explode.
Predicting flares and CMEs
The active regions that spark solar flares and CMEs are often marked by sunspots, planet-size areas of the sun that appear darker than their surroundings at visible wavelengths.
First recorded thousands of years ago by Chinese astronomers peering at the sun with naked eyes, telescopic observations and data collection of sunspots began in the 1600s. A pattern has emerged from the hundreds of years of data: a cycle of solar activity that peaks every 11 years. The sun is currently at or near its solar maximum.
Today, scientists still map sunspots in detail. “We’re looking at each single sunspot group and what their magnetic structure is,” Dahl says. Operationally, it’s currently impossible to predict exactly when a solar flare will occur, but he says researchers can model the probability of a flare occurring in the next 3 days based on the data provided by these observations.
The energy from the most powerful flares can obliterate high-frequency (HF) radio wave signals, so flare forecasts are important to industries, such as aviation, that use HF radio for communication. But because most of that energy comes from photons and X-rays traveling at the speed of light or charged particles traveling near the speed of light, “when we see a solar flare, the effect is already ongoing in the outer atmosphere of our planet,” Dahl says.
An image of the sun shows a bright flash of light and plasma loops in the corona, tinted yellow, and the extremely hot material in flares, tinted blue.
On Feb. 21, 2024, NASA’s Solar Dynamics Observatory captured an ultraviolet image of a solar flare. Scientists can’t yet precisely predict when a flare will occur, only its probability.
Credit:
NASA/Solar Dynamics Observatory
When a CME erupts from the sun, earthlings have a bit more time to prepare because the bubble of plasma travels more slowly than a flare.
Forecasters such as those at NOAA and other members of the International Space Environment Service can use satellite and ground-based measurements to determine the CME’s trajectory and whether it’ll hit Earth. But “we know nothing about the dynamics and the structure of that CME whatsoever until it arrives 1 million miles away from Earth where we have a few satellites,” Dahl says. At an average speed, a CME will crash into Earth 45–60 min after hitting those satellites. “At their quickest, they can be here in 10 to 15 minutes,” Dahl adds.
Because CMEs can cause blackouts, “the power grid needs as much advance notice of these storms as they can possibly get,” Dahl says. So his team has taken strides to send out a warning of a potentially hazardous CME before it even reaches a satellite.
To initiate the warning, Dahl hops on the phone. “It’s called the NERC hotline,” he says. “NERC stands for North American Electric Reliability Corporation. That’s who controls the power grid for all the southern Canadian provinces and all the 48 mainland United States.”
In the last 2 years, scientists have recorded many G4 events and one G5 event. And through the storms, the power stayed on in the US.
Improving flare models
Some researchers are hoping to improve solar flare models with new observations. For example, advanced telescope optics recently allowed researchers in CU Boulder’s Kazachenko group to capture images of a recent flare in extraordinary detail using the most powerful solar telescope on Earth: the Daniel K. Inouye Solar Telescope.
The images produced show light emitted by hydrogen atoms in the plasma of the solar surface and atmosphere during a large solar flare (Astrophys. J. Lett. 2025, DOI: 10.3847/2041-8213/adf95e). Fine loops of darker plasma outline the structure of the magnetic field immediately after reconnection, while bright ribbons of orange show where accelerated particles smash into the solar surface.
With advanced optics, researchers such as Maria Kazachenko can now capture very-high-resolution images of solar flares using light emitted by hydrogen ions in the plasma. The bright ribbons of orange light visible on the sun’s surface show the foot of arching, invisible magnetic field lines. The scale of this image is about 4 Earth-diameters on each side.
Credit:
NSF/NSO/AURA
“We are trying to understand the enigma of how solar flares happen,” Kazachenko says. The new images may hold a missing piece of the puzzle.
“There is a promise that these fine structures would be able to tell us the full story of magnetic reconnection,” Kazachenko says. A better understanding of magnetic reconnection could help researchers better predict flares. After all, you can’t forecast what you don’t understand, she adds.
By reanalyzing solar spectra, a group of scientists led by solar physicist and applied mathematician Alexander Russell at the University of St. Andrews also recently revealed new insights into the temperature of the plasma at the heart of solar flares.
Scientists can determine these temperatures in a few ways, Russell says. X-ray blackbody radiation, elements’ ionization states, and emission-line ratios from specific elements are all related to the temperature of electrons in a flare. Each of these measures has independently pointed to those electrons being about 10 million–15 million °C, Russell says.
But ever since the first solar space missions recorded spectra, it has been clear that spectral emission lines “are much broader than you would expect based on the electron temperature,” Russell says. “The question has been, why?”
By combining an up-to-date understanding of solar flares densities with data from recent space physics missions and supercomputer simulations, Russell came up with an answer: magnetic reconnection heats ions far more efficiently than electrons. Ion temperatures can reach as high as 60 million–100 million °C, he says, more than 6.5 times as hot as the electrons in the flare (Astrophys. J. Lett. 2025, DOI: 10.3847/2041-8213/adf74a).
“A lot of our models that we use to try and predict solar flares and understand them have been founded on the idea that the ions and electrons have the same temperature,” Russell says. But if ions are preferentially heated, those models need to be updated, he says.
Together, new ground-based observations, calculations, and dedicated space weather satellite missions all aim to help scientists understand solar flares and CMEs. That understanding will feed into predictive models like those used at NOAA’s Space Weather Prediction Center. “We’re focused on keeping society safe with actionable space weather information. That’s what we’re doing,” Dahl says. “The aurora is just part of the sideshow.”
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