Breaking news: Webb’s coldest instrument reaches operating temperature

Credit image: ESA/NASA/C. Gunn - MIRI integration into JWST payload module
Credit image: ESA/NASA/C. Gunn - MIRI integration into JWST payload module

Article by: Andacs Robert Eugen, on 13 April 2022, at 12:43 pm Los Angeles time

The James Webb Telescope's medium-infrared instrument has reached operating temperature and is ready for calibration and Webb's future observations.

According to NASA, Webb will be able to see galaxies that formed after the Big Bang.

Until then, however, all tools must be prepared for successful observations and research. Thus, Webb's tools need to be cooled down a lot.

Recently, Webb's Mid-Infrared Instrument (MIRI) has reached operating temperatures below 7 K (-447 degrees Fahrenheit, or -266 degrees Celsius).

The temperature was reached on April 7, but now the instrument is even colder.

"I am delighted that after so many years of hard work by the MIRI team the instrument is now cold and ready for the next steps. That the cooler worked so well is a major achievement for the mission," said Gillian Wright, European principal investigator for MIRI and Director of the UK Astronomy Technology Centre (ATC).

An electrically powered cryocooler was used for cooling. 

The instrument cooled as much as it could in the shadow of Webb's sunshade, reaching 90 K, but it had to be much lower.

The team that coordinates Webb lowered the temperature until it reached 15 K. Then followed the "clamping point", when the instrument cooled from 15 K to 6.4 K.

Webb has a total of 4 infrared detectors. As all objects outside the Solar System (exoplanets, stars, galaxies) emit infrared waves, the 4 instruments will have to detect them.

Thus, their cooling will allow Webb to make some spectacular observations.

The MIRI instrument detects longer infrared wavelengths than the other 3, so it needs to be even cooler.

Another reason why these instruments need to be cold is because of the so-called dark current or false current.

It is created by the vibration of atoms and is also called false because it mimics a true signal in detectors.

This current gave the false impression that the detectors had been struck by light from an external source.

This confuses astronomers because it is a false impression that can complicate research.

And astronomers want to find real signals, not fake signals.

Cooling the instrument makes the vibrations in the detectors less and does not confuse the research.

"We spent years practicing for that moment, running through the commands and the checks that we did on MIRI," said Mike Ressler, project scientist for MIRI at JPL. "It was kind of like a movie script: Everything we were supposed to do was written down and rehearsed. When the test data rolled in, I was ecstatic to see it looked exactly as expected and that we have a healthy instrument."

"I am immensely proud to be part of this group of highly motivated, enthusiastic scientists and engineers drawn from across Europe and the USA," said Alistair Glasse, MIRI instrument scientist at the ATC in Edinburgh, Scotland. "This period is our 'trial by fire' but it is already clear to me that the personal bonds and mutual respect that we have built up over the past years is what will get us through the next few months to deliver a fantastic instrument to the worldwide astronomy community."

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