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James Webb, Halley's Comet may be set for cosmic dust-up

Comet debris is right in JWST's path, and could further damage its sensitive mirror

The James Webb Space Telescope is predicted to pass through Halley's Comet's debris trail next year, meaning that particles could further endanger its sensitive primary mirror.

JWST's mirror is exposed to the vacuum of space, and while that means it produces images with far more clarity than Hubble, it also has nothing to shield it from sand grain-sized debris traveling at 10km/second, or 6.2 miles/second (over 22,300mph). 

Small debris can cause serious damage, such as the May impact on Webb's mirror that caused irreparable harm, but which NASA was able to correct for.

Halley's Comet itself won't be back in the inner solar system until 2061, but the bright tail trailing out behind it is filled with dust, debris and ice shed by the comet. It's that debris field that JWST is predicted to enter in 2023 and 2024. 

Webb wasn't built to last

According to Nature, meteor shower dust like that left behind by Halley only constitutes around 5 percent of the impact risk to Webb, while the rest is from random hits from stray dust. Scientists have long planned for such hits during Webb's lifetime, but May's unexpected impact has had scientists re-evaluating the potential for serious damage and developing custom meteor shower forecasts at Lagrange point 2, where Webb sits in space.

With those forecasts, the space telescope's operators can reposition the telescope to avoid incoming dust, but such forecasts still leave Webb exposed to unpredictable hits from single micrometeoroids, as was the case in May.

Hubble, by contrast, which sits in low earth orbit and is encased within a tube, is still operating after more than 30 years. 

Webb gets around Hubble's primary limitation of having a limited observational wavelength in a couple of ways: It doesn't lock its mirror in a tube, and it sits far enough from the Sun that it can offset heating that limits wavelengths. While those elements make Webb a better observer of the cosmic condition, it also means it's not serviceable once deployed and is exposed to lots of potential damage. 

NASA said the minimum baseline for JWST's mission duration is five years, with the agency hoping to get a decade out of the telescope. The fuel in JWST is enough to keep it in position and transmitting data for longer than a decade, NASA said, but that's if a grain of sand doesn't turn Webb into a $10 billion lesson in protecting sensitive equipment. ®

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