On June 8, NASA announced that its new powerful space observatory, the James Webb Space Telescope, now has a small dent in one of its primary mirrors after it was bombarded by a larger-than-expected micrometeoroid in space. The news came as a bit of a shock, given that the impact came just five months into the telescope’s tenure in space — but such impacts are simply an inevitable aspect of space travel, and more impacts are sure to come.
Contrary to what the name might suggest, space isn’t exactly empty. Within our solar system, tiny particles of space dust whiz through the regions between our planets at tremendous speeds that can reach tens of thousands of kilometers per hour. These micrometeoroids, no larger than a grain of sand, are often small pieces of asteroids or comets that broke away and are now orbiting the Sun. And they are everywhere. A rough estimate of the small meteoroids in the inner solar system puts their total mass at about 55 trillion tons (if they were all combined into one rock, it would be about the size of a small island).
So if you send a spaceship into space, your hardware is sure to get hit by one of those little space rocks at some point. Knowing this, spacecraft engineers will design their vehicles with specific protections to shield them from micrometeorite impacts. They often contain a so-called Whipple shield, a special multi-layer barrier. When the shield is hit by a micrometeoroid, the particle penetrates the first layer and shatters further, striking the second layer with even smaller particles. Such shielding is typically used around sensitive spacecraft components for added protection.
But with NASA’s James Webb Space Telescope, or JWST, it’s more difficult. The telescope’s gold-coated mirrors must be exposed to the space environment to properly collect light from the distant universe. And while these mirrors are built to withstand some impacts, they’re more or less easy prey for larger micrometeorite impacts like the one that hit JWST in May. Although the micrometeoroid was still smaller than a grain of sand, it was larger than NASA anticipated – enough to damage one of the mirrors.
Spacecraft operators are modeling the micrometeoroid population in space to better understand how often a spacecraft might be hit in a particular part of the solar system — and what particle size their hardware might be hitting. But even then, it’s not a foolproof system. “Everything is probable,” says David Malaspina, an astrophysicist at the University of Colorado who focuses on the effects of cosmic dust on spacecraft The edge. “All you can say is, ‘I have this chance of being hit by a particle that size.’ But whether you ever do it or not is up to chance.”
Micrometeoroids have a wide range of formation histories. They may be the remnants of high-speed space collisions that pulverize space rocks into tiny pieces. Asteroids and comets are also bombarded by space particles and photons from the Sun over time, causing tiny pieces to break off. An asteroid can also get too close to a large planet like Jupiter, where the strong gravitational pull tears off rocks. Or an object can get too close to the sun and get too hot, causing the rock to expand and break into pieces. There are even interstellar micrometeoroids just zipping through our solar system from more distant cosmic neighborhoods.
How fast these particles travel depends on which region of space they are in and the path they take around our star, averaging about 45,000 miles per hour, or 20 kilometers per second. Whether they hit your spaceship or not also depends on where your vehicle is in space and how fast it is moving. For example, NASA’s Parker Solar Probe is currently the closest man-made object to the sun, moving at a top speed of more than 400,000 miles per hour. “It goes to the 4-yard line compared to Earth, which is entirely in an end zone,” says Malaspina, who has focused on studying micrometeorite impacts on Parker Solar Probe. It also moves through the densest part of a region called the zodiacal cloud, a thick disk of space particles that permeates our solar system. So the Parker Solar Probe is sandblasted more often than JWST – and it hits these particles at incredibly high speeds than it would hit the telescope.
The Parker Solar Probe gives us a better understanding of micrometeoroids around the Sun, but we also have a pretty good understanding of the populations around the world. Whenever a micrometeoroid hits the upper atmosphere around our planet, it burns up and produces meteoric smoke – fine smoke particles that can be measured. The amount of this smoke can tell us how much dust hits the earth over time. In addition, experiments have been conducted on the International Space Station, attaching materials to the outside of the orbiting laboratory to see how often they are bombed.
While JWST lives about 1 million miles from Earth, that’s still relatively close. Scientists also have an idea of what’s out there based on other missions that have been sent into an orbit similar to JWST. And most things hitting the telescope aren’t that big of a deal. “Spaceships get hit by little ones all the time,” says Malaspina. “By little, I mean fractions of a micron — much, much, much smaller than a human hair. And for the most part, spacecraft don’t even notice them.” In fact, JWST had been hit by small micrometeoroids four times before being hit by the larger micrometeoroid in May.
NASA modeled the micrometeoroid environment before launching JWST, but given the recent impact, the agency has convened a new team to refine their models and better predict what might happen to the telescope after future impacts. Current micrometeoroid modeling will try to predict things like debris propagating through an orbit when an asteroid or comet breaks apart. This type of debris is more dynamic, Malaspina says, making it harder to predict.
Ultimately, however, the prediction will simply give you more knowledge about it if a spaceship could be hit by a large speck of dust. One-off charges like this are simply inevitable. JWST will continue to be blown up over time, but it was a contingency NASA was always prepared for. “You just have to live with the likelihood that at some point you’ll be hit by a dust particle that size, and you’re just doing the best you can with the technology,” says Malaspina.