As you read this sentence, your body is being bathed in cosmic radiation. Don’t worry. It’s a small dose, only about five muons per second, but it’s there.
While the Earth’s magnetosphere and atmosphere protect us from an onslaught of cosmic radiation, astronauts, including those aboard the Artemis II mission, don’t have the luxury of our planet’s natural defenses.
For humanity to become a truly interplanetary species, our space organizations need to overcome the dangers of cosmic radiation.
“NASA has known about this space radiation for 40 years and they’ve been studying the most important parts,” said Daniel Cebra, professor and chair of the UC Davis Department of Physics and Astronomy. “The part they haven’t studied is high-energy nuclear collisions and that’s how a high-energy nuclear physicist gets involved.”
Cebra, the UC Davis speaker for the April 2026 Astronomy on Tap event at Sudwerk Brewing Co., discussed galactic cosmic rays, a particularly dangerous form of high-energy cosmic radiation.
“Various objects out there, like supernovae, can emit energetic charged particles that create a flux of radiation in space,” said Cebra, noting that this radiation is constant. “This radiation is a hazard for long-duration missions. It’s a hazard for both personnel and equipment, and data-driven simulations are the best way for NASA to understand how to best protect equipment and astronauts on long-duration missions.”
Solar wind and solar energetic particles from solar flares
Space agencies contend primarily with three different kinds of space radiation, according to Cebra,
The first is solar wind.
“The sun is a boiling, seething mass of plasma and just like watching a pot simmer, there’s stuff that boils off. That’s the solar wind,” he said, noting that these protons are between one to 10 kilo-electron volts of energy and can pass through a few microns of water. “That’s low energy by our standards…so as long as you’re inside your spaceship, you’re fine.”
Solar energetic particles are the second source of space radiation. Emanating from solar flares, solar energetic particles can reach up to a few hundred mega-electron volts of energy and pass through tens of centimeters of water.
Luckily, the Earth’s magnetosphere protects us from most of the radiation from solar wind and solar flares. However, we can still see evidence of this solar radiation when it manifests as the aurora borealis.
In outer space, it’s a different story.
“[Solar energetic particles] will pass through the walls of your spaceship; they will irradiate the astronauts; they will irradiate your electronics,” Cebra said. “Your computers, your instruments will all fail.”
But “we actually know how to shield from the solar flares,” he added. “If you’re in a spacecraft going to Mars and a flare [happens], you orient your spacecraft and you hide behind your water supply. That’s your radiation shelter.”
The third source of space radiation, and by far the most dangerous, are galactic cosmic rays.
What are galactic cosmic rays?
Outpowering both solar winds and solar flares, galactic cosmic rays range in the hundreds of mega-electron volts of energy up to giga-electron volts of energy. They can pass through hundreds of meters of material and even penetrate water shields.
“You can’t stop them and you can’t hide from them,” said Cebra, noting that galactic cosmic rays are coming from events across the galaxy. “We know the elemental composition. We see peaks of carbon, oxygen, silicon and iron. That’s the signature of a supernova, that’s stellar burning.”
Any electronic devices going into outer space consistently undergo radiation hardness testing. UC Davis conducts such testing at the Crocker Nuclear Laboratory.
With NASA’s recent return to the moon and its scheduled future missions, Cebra said the space agency is prioritizing high-energy measurements (those in the giga-electron volts range) as the next area of study for space radiation shielding.
“There are almost no data above the energy of one giga-electron volt,” he said.
That’s where Cebra’s research group can make a difference. They study high-energy nuclear collisions above one giga-electron volt.
Applying high-energy nuclear physics to space travel
Historically, Cebra’s research group has focused on heavy nuclei collisions, specifically using gold, to better understand phase transitions of matter at the quantum level.
Though there isn’t any gold in galactic cosmic rays and spaceships aren’t made of gold, Cebra said the particle accelerators used in his team’s experiments can be tuned to produce other beams of interest, including those that will make a difference to space travel.
“I have installed carbon, aluminum and nickel targets to allow measurements to be made which will be useful to NASA,” he said.
Information gleaned from such experiments can then be used to create data-driven simulations that will help NASA prepare for future long-duration space missions, ensuring both equipment and astronaut safety.
But Cebra’s science currently faces a temporary roadblock.
In February 2026, the Relativistic Heavy Ion Collider, or RHIC, at Brookhaven National Laboratory was shut down for upgrades, resulting in Cebra’s research group being unable to hit their targets of interest.
However, hope is not lost.
“We are still in the game because the RHIC facility is being upgraded to become the Electron Ion Collider,” Cebra said. “I have already proposed that we make these measurements at that new facility when it opens.”
YOU MAY ALSO LIKE THESE STORIES
Hunting for Cosmic Dawn With the James Webb Space Telescope
At the March Astronomy on Tap event at Sudwerk Brewing, Professor Tucker Jones, Department of Physics and Astronomy, describes how the James Webb Space Telescope is being used to pinpoint the cosmic dawn, an early period in the universe’s history when the first stars and galaxies formed.
A New Road Map to Room Temperature Superconductors
The discovery of room-temperature superconductors would open a huge range of applications and new technologies. There are no physical laws that rule out such materials, according to a recent perspectives article by a group of scientists including Warren Pickett, Distinguished Professor Emeritus of physics and astronomy at UC Davis.