Key Takeaways on the Van Allen Belts:
In 1958, James Van Allen discovered far fewer cosmic rays than expected using a cosmic-ray detector and suggested that a belt of strong radiation may have damaged the device. The belts were therefore named in honor of Van Allen.
Van Allen belts are a big, energetic stew of charged particles that encircle Earth. The particles of the outer belt come from the sun by means of solar wind and are trapped by Earth’s magnetic field, or magnetosphere. The particles in the inner belt originate when cosmic rays interact with Earth’s atmosphere.
This intense radiation makes space travel tricky. Astronauts must pass through the Van Allen belts to get to outer space. To do this safely, they must plot their route so they will pass through the weakest part of the belts and spend as little time as possible in this region.
Explorer 1, the first U.S. satellite (launched in 1958, three months after the U.S.S.R. launched Sputnik), found a big surprise in space: the Van Allen belts, rings of radiation that to this day are still being studied and are still complicating space travel.
The satellite carried a cosmic-ray detector designed by physicist James Van Allen of the University of Iowa. The team included the detector because they expected to encounter cosmic rays, which they had recently discovered through balloon measurements.
When Van Allen’s device detected far fewer cosmic rays than had been expected, Van Allen hypothesized that a belt (or two, as it turned out) of strong radiation may have damaged the device. Another satellite, launched two months later, confirmed this. The belts were named in honor of Van Allen.
What Are the Van Allen Belts?
Shaped like two enormous donuts, the Van Allen belts are a big, energetic stew of charged particles that encircle Earth. The particles of the outer belt come from the sun by means of solar wind and are trapped by Earth’s magnetic field, or magnetosphere, explains Mary Hudson, a space physicist at Dartmouth University. The particles in the inner belt originate when cosmic rays interact with Earth’s atmosphere.
“When the cosmic rays strike the atmosphere, they actually have nuclear collisions,” she says. “They collide with the nuclei of atoms and kick out neutrons, and neutrons decay into protons and electrons, on average, 15 in 15 minutes.”
How Astronauts Can Pass Through the Belts
This intense radiation makes space travel tricky. Astronauts must pass through the Van Allen belts to get to outer space. To do this safely, they must plot their route so they will pass through the weakest part of the belts and spend as little time as possible in this region.
NASA’s Apollo 8 was the first crewed mission to pass through the Van Allen belts on its way to orbit the moon in 1968. The next year, Apollo 11 put humans on the moon for the first time. In that historic trip, the astronauts plotted their trip so that they spent only 52 minutes in the Van Allen belts, absorbing far less radiation than the maximum considered safe.
Read More: How Does Earth’s Magnetic Field Work?
Why the Van Allen Belts Matter for Space Travel
The Van Allen belts aren’t the only issue when it comes to staying safe from radiation in space. Solar storms are also dangerous.
“There was an enormous solar particle event in August of 1972 that happened to occur between two Apollo missions,” recalls Hudson, whose specialty is space weather and solar activities. “If it had occurred during one of the Apollo missions, that would have been very hazardous for the astronauts.”
Hudson is on a National Academies of Sciences committee that is studying how best to send people to the moon to do science experiments. She points out that now that we’re planning to send astronauts back to the moon, we’re going to have to give some attention to how solar storms might affect these astronauts. And because they will be much longer, missions to Mars will take even more careful weather calculations.
“I think we have much better forecast capability now than we did during the Apollo days,” she says. “So I think that's perfectly doable.”
Van Allen Belts and the Safety of Satellites
The Van Allen belts aren’t a problem just for space exploration. They can damage satellites, too, and we’re putting up a lot of satellites these days. Satellites are generally set in low Earth orbit, below the heart of the radiation belts.
But communications companies in some countries, Hudson says, are putting up satellites that spend a lot of time in locations that are dangerous to satellites. This means they will deteriorate faster, create more space debris, and need to be replaced more frequently.
But satellites in low Earth orbit can be problematic, too. “The ones down in low Earth orbit, like Starlink satellites, likely have a planned lifetime that's a lot less than 25 years, just because they're at such low altitude,” Hudson says.
Understanding the Van Allen belts and space weather in general is essential for safe space travel. And it’s turning out that it’s essential for communications down here on Earth, too.
Read More: Solar Flares are Stunning but are They Dangerous? Here's What to Know
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
The University of Iowa. James Van Allen, Space Pioneer
NASA. Explorer 1 Overview
Avery Hurt is a freelance science journalist. In addition to writing for Discover, she writes regularly for a variety of outlets, both print and online, including National Geographic, Science News Explores, Medscape, and WebMD. She’s the author of Bullet With Your Name on It: What You Will Probably Die From and What You Can Do About It, Clerisy Press 2007, as well as several books for young readers. Avery got her start in journalism while attending university, writing for the school newspaper and editing the student non-fiction magazine. Though she writes about all areas of science, she is particularly interested in neuroscience, the science of consciousness, and AI–interests she developed while earning a degree in philosophy.
