James Webb Runs Colder Than Deep Space Itself

To see the oldest light in the universe, this telescope has to stay colder than almost anything humans have ever operated.

James Webb hunts infrared light, which is really heat. A warm telescope would blind itself with its own glow, so it must stay below minus 223 degrees Celsius.

To pull that off, engineers gave it a sunshield the size of a tennis court, five paper-thin layers blocking the Sun, Earth, and Moon at once. On the sunny side, temperatures soar past 100 degrees Celsius. A few meters away on the shaded side, the mirror sits near minus 235. It orbits a point a million miles from Earth, where the Sun, our planet, and the Moon all stay behind that shield at once.

There is no going back to fix it. Unlike Hubble, Webb is far too distant for any astronaut to reach. It has to survive alone in the cold and dark, working perfectly, as long as its fuel lasts.

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