A Micrometeoroid Hit The James Webb Space Telescope’s Primary Mirror

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NASA’s James Webb Space Telescope (JWST) is on the verge of beginning its science operations, so the recent news that it has suffered a micrometeoroid impact is concerning. The space observatory is the long-awaited successor to Hubble, and it could serve as our window to the wider universe for the next 20 years, provided it doesn’t get pelted by too many space rocks. Thankfully, NASA says the impact, which occurred between May 23th and 25th did not cause any serious damage. Webb should be right as rain after a realignment. 

The JWST has been 20 years and more than $10 billion in the making, but it finally launched at the end of 2021. While the engineering and construction process was plagued by delays, the observatory has performed perfectly in space. The launch went so well that Webb was able to save enough fuel to double its expected lifespan, and the early test images suggest the optics are literally flawless. Well, they were. NASA says the micrometeoroid hit was larger than those it modeled during the design and testing phase, and it impacted one of Webb’s primary mirror segments. 

Webb sports a huge array of hexagonal mirror segments, poking up above the spacecraft bus like a sunflower. Webb has a total mirror area of 273 square feet versus just 43 square feet for Hubble. That’s a lot of surface area that could invite impact by tiny space rocks. However, NASA says it designed Webb to withstand this kind of abuse. While a micro-meteoroid only weighs a fraction of a gram, it can be moving so fast that it can cause damage. 

Webb was kept ultra-clean on the ground to ensure it had the best reflectivity and overall sensitivity, which is one of the reasons astronomers are so excited about what it will do. That gives the telescope a little leeway when it comes to degradation over time. “With Webb’s mirrors exposed to space, we expected that occasional micrometeoroid impacts would gracefully degrade telescope performance over time,” said Lee Feinberg, Webb optical telescope element manager at NASA Goddard.

Because it uses a segmented Korsch-style mirror, NASA will be able to adjust the affected panel to minimize the effect of the impact. Currently, NASA believes this impact will not affect the telescope’s capabilities at all. The agency has also formed a dedicated team to investigate additional methods to mitigate future micrometeoroid impacts. 

We expect Webb to begin its science operations soon. By operating in the mid-infrared, Webb will be able to peer through clouds of dust and gas that would have blocked Hubble and larger ground-based telescopes. Some of the first targets will be exoplanets, which are too small and dim to appear in Hubble’s scopes. This is just the beginning of what could be a 20-year mission for the most advanced optical instrument ever built, micrometeoroids be damned.

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