Soon, MIRI will monitor Saturn’s poles.
The supercold camera MIRI on the James Webb Space Telescope is now again operating in full science mode after a technical issue with its grating disc led researchers to stop some observations.
Astronomers can select which wavelengths of light to use to examine the surrounding universe using the grating wheel on the Mid-Infrared Instrument (MIRI) of the Medium Resolution Spectrometer (MRS) on the James Webb Space Telescope. The mission team was forced to halt observations in the impacted mode in August after the wheel, which is only utilised in one of MIRI’s four observing modes, began to exhibit signs of friction.
Engineers studied the issue remotely for weeks before coming to the conclusion that “increased contact forces between the wheel central bearing assembly’s sub-components under certain conditions” were to blame, according to a statement from the Space Telescope Science Institute (STScI) in Baltimore, which is in charge of Webb’s operations (opens in new tab).
The engineers have now given the go-ahead for the impacted spectroscopic mode to start operations and are creating a list of guidelines for using the impacted wheel safely, according to STScI in the release.
On November 2, 2022, “an engineering test demonstrating updated operational parameters for the grating wheel mechanism was successfully completed,” according to STScI. “In order to take advantage of a rare opportunity to see Saturn’s polar regions, MIRI is resuming MRS science observations. In order to prepare MIRI’s MRS mode for a return to full science scheduling, the JWST team will plan more MRS science observations, initially at a highly coordinated cadence with extra trending measurements to monitor the new operational regime of the mechanism.”
When in MRS mode, MIRI instead records light spectra, which are effectively light absorption fingerprints that show the chemical compositions of the objects being seen.
The MRS outage has not affected MIRI’s three other observation modes, imaging, coronagraphic imaging, or low-resolution spectroscopy. The famed Pillars of Creation were captured in one of the spectacular photographs taken by the supercold camera, which displayed the delicate dusty formation in unsettling detail.
Of all Webb’s sensors, MIRI, which specialises in detecting mid-infrared wavelengths, needs the coldest temperatures to function well. The telescope’s location and its massive sunshield are all that are needed for the other three instruments, NIRCam, NIRSpec, and FGS/NIRISS, to maintain temperatures of minus 369.4 degrees Fahrenheit (minus 223 degrees Celsius). However, MIRI needs additional cryocoolers to reach minus 447 degrees F. (minus 266 degrees C). That is just seven degrees Celsius (12 degrees Fahrenheit) above the point at which atoms cease to move. Any additional heat would reduce the sensitivity of MIRI’s observations because infrared light, which is essentially heat, is what the instrument measures.