The Mid-Infrared Instrument (MIRI) reached -266°C on April 7, just over three months after its launch on Christmas day in 2021.
Along with Webb’s three other instruments, MIRI initially cooled off in the shade of Webb’s tennis-court-size sunshield, dropping to about -183°C, but further temperature drops required an electrically powered cryocooler.
Analyn Schneider, project manager for MIRI, said: “The team was both excited and nervous going into the critical activity. In the end it was a textbook execution of the procedure and the cooler performance is even better than expected.”
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. So do other warm objects, including Webb’s own electronics and optics hardware. Cooling down the four instruments...