James Webb Space Telescope's MIRI instrument goes super-cold
JWST will see the first galaxies to form after the big bang, but for that it's instruments needs to cool down
On April 7, Webb’s Mid-Infrared Instrument (MIRI) reached its final operating temperature below 7 kelvins (minus 447 degrees Fahrenheit, or minus 266 degrees Celsius).
Last week, the team passed a milestone called the “pinch point,” when the instrument goes from 15 kelvins (minus 433 F, or minus 258 C) to 6.4 kelvins (minus 448 F, or minus 267 C).
The low temperature is necessary because all four of Webb’s instruments detect infrared light – wavelengths slightly longer than those that human eyes can see.
Distant galaxies, stars hidden in cocoons of dust, and planets outside our solar system all emit infrared light. But so do other warm objects, including Webb’s own electronics and optics hardware.
MIRI detects longer infrared wavelengths than the other three instruments, which means it needs to be even colder.
Requires more cooling
Another reason JWST detectors need to be cold is to suppress something called dark current.
It is created by the vibration of atoms in the detectors themselves. Dark current mimics a true signal in the detectors, giving the false impression that they have been hit by light from an external source.
So by reducing the temperature means less vibration, which in turn means less dark current.
Once MIRI reached a frigid 6.4 kelvins, scientists began a series of checks to make sure the detectors were operating as expected.
The team will conduct these preparations alongside calibration of the other three instruments, delivering Webb’s first science images this summer.