On June 8, NASA revealed that its new high-powered space observatory, the James Webb Space Telescope, now shows a small dimple in one of its primary mirrors after being pelted by a larger-than-expected micrometeoroid in deep space. The news came as a shock because the impact occurred in the telescope’s spacecraft just five months ago — but such attacks are simply an unavoidable aspect of space travel, and more booms are sure to come.
Despite what the name implies, the space isn’t exactly empty. Within our solar system, tiny bits of space dust buzz through the regions between our planets at speeds as high as tens of thousands of miles per hour. These micrometeoroids, no bigger than a grain of sand, are often small pieces of asteroid or comet that have broken off and are now orbiting the sun. And they are everywhere. A rough estimate of small meteoroids in the inner solar system puts their combined total masses at about 55 trillion tons (if they were all combined into one rock, it would be about the size of a small island).
That means if you send a spacecraft into deep space, at some point your hardware will definitely be hit by one of these small pieces of space rock. Knowing this, spacecraft engineers will build their vehicles with certain protections to guard against micrometeoroid attacks. They often include something called Whipple shielding, which is a special multi-layer barrier. If the shield is hit by a micrometeoroid, the particle will pass through the first layer and fragment even further, hitting the second layer by 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 trickier. The telescope’s gold-coated mirrors must be exposed to the space environment to properly capture the light from the distant universe. And while these mirrors are built to withstand some shocks, they’re more or less sitting ducks for larger micrometeoroid strikes, like the one that hit JWST in May. Although the micrometeoroid was still smaller than a grain of sand, it was larger than what NASA expected — enough to cause damage to one of the mirrors.
Spacecraft operators are modeling the population of micrometeoroids in space to gain a better understanding of how many times a spacecraft can be hit in a particular part of the solar system — and what sized particles can damage their hardware. But even then, it’s not a foolproof system. “It’s very likely,” said David Malaspina, an astrophysicist at the University of Colorado who studies cosmic dust impacts on spacecraft. The edge† “All you can say is, ‘I have the chance to be hit by this sizeable particle.’ But whether you ever do it or not, that depends on chance.”
Micrometeoroids have a wide variety of origin stories. It could be the remains of high-velocity collisions in space, which pulverize space rocks into tiny pieces. Over time, asteroids and comets are also bombarded by space particles and photons from the sun, breaking off small pieces. An asteroid can also get too close to a large planet like Jupiter, where strong gravitational pull rips apart pieces of rock. Or an object can get too close to the sun and become too hot, causing the rock to expand and break into pieces. There are even interstellar micrometeoroids just passing through our solar system from more distant cosmic neighborhoods.
How fast these particles move depends on the area of space they are in and the path they travel around our star, at an average speed of about 45,000 miles per hour or 20 kilometers per second. Whether they will encounter your spacecraft also depends on where your vehicle lives 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 600,000 miles per hour. “It comes down to the 4-yard line, compared to Earth lying all the way in one end zone,” said Malaspina, who has focused on studying micrometeoroid effects on Parker Solar Probe. It also moves through the densest part of an area called the zodiac cloud, a thick disk of space particles that permeates our solar system. So the Parker Solar Probe gets sandblasted more often than JWST — and it hits these particles at incredibly high speeds than the telescope would be hit.
The Parker Solar Probe gives us a better understanding of micrometeoroids around the sun, but we also have a pretty good understanding of the population around the earth. Whenever a micrometeoroid hits the upper atmosphere around our planet, it burns up, creating 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, there have been experiments on the International Space Station, where materials have been mounted on the outside of the orbiting laboratory to see how often they are bombed.
Even though 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 sent to a similar orbit to JWST. And most things that hit the telescope aren’t that big of a deal. “Spacecraft are constantly being hit by little ones,” Malaspina says. “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 it.” In fact, JWST was hit by small micrometeoroids four times before being hit by the larger micrometeoroid in May.
NASA modeled the micrometeoroid environment before JWST launched, but in light of 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 attempt to predict how debris will spread through orbit if an asteroid or comet breaks apart. That kind of debris is more dynamic, Malaspina says, making it harder to predict.
However, at the end of the day, prediction will simply give you more knowledge about: when a spacecraft can be hit by a large dust particle. One-off effects like these are just unavoidable. JWST will continue to come under attack over time, but it was a possibility NASA was always prepared for. “You just have to live with the chance that you’ll end up being hit by a dust particle of any size, and you’re just doing your best with the engineering,” Malaspina says.
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