This illustration shows the cold side of the Webb Telescope, where the mirrors and instruments are located. Credit: Northrop Grumman
Recently, NIRISS, one of the four primary science instruments on NASA’s James Webb Space Telescope, completed its post-launch preparations and was declared science-ready. Now the second of Webb’s four main science instruments, known as the Mid-Infrared Instrument (MIRI), has also completed its post-launch preparations and is now ready for science.
“We are thrilled that MIRI is now a working, state-of-the-art instrument with better-than-expected performance in all its capabilities.” — Gillian Wright and George Riecke
MIRI’s coronagraphic imaging capability, which uses two different styles of masks to intentionally block starlight from hitting its sensors when trying to make observations of the planets orbiting the star, was the last MIRI mode to be ticked off. These custom masks allow scientists to directly detect exoplanets and study dust disks around their host stars in a way that has never been done before.
Along with Webb’s three other instruments, MIRI was initially cooled in the shadow of Webb’s tennis court-sized sun shield to about 90 Kelvin (minus 298 degrees Fahrenheit or minus 183 degrees Celsius). To do what the science intended, that meant lowering it to less than 7 kelvins — just a few degrees above the lowest temperature matter can reach — by using an electrically powered cryocooler. These extreme operating temperatures allow MIRI to deliver mid-infrared images and spectra with an unprecedented combination of sharpness and sensitivity.
Webb MIRI spectroscopic animation: The light beam coming from the telescope is then shown in deep blue, entering the instrument through the measurement mirror located at the top of the instrument and acting as a periscope. A series of mirrors then redirects the light to the bottom of the instruments, where an array of 4 spectroscopic modules resides. Once there, the light beam is split by optical elements called dichroics into 4 beams corresponding to different parts of the mid-infrared region. Each beam enters its own integral field unit; these components split and reformat light from the entire field of view, ready to be dispersed into spectra. This requires the light to be bent, reflected and split many times, making this possibly one of Webb’s most complex light paths. To complete this incredible journey, the light of each beam is scattered by gratings, creating spectra that are then projected onto 2 MIRI detectors (2 beams per detector). An incredible feat of engineering! Credit: ESA/ATG medialab
“We are thrilled that MIRI is now a working, state-of-the-art instrument with better-than-expected performance in all its capabilities.” Our multinational commissioning team did a fantastic job getting MIRI ready in just a few weeks. We now celebrate all the people, scientists, engineers, managers, national agencies, the European Space Agency (ESA) and NASA who have made this instrument a reality as MIRI begins to explore the infrared universe in ways and to depths never seen before,” said Gillian Wright , MIRI European Principal Investigator at the UK Astronomical Technology Centre, and George Riecke, MIRI Scientist at the University of Arizona. MIRI was developed as a partnership between NASA and ESA (the European Space Agency), with NASA’s Jet Propulsion Laboratory leading the US effort and a multinational consortium of European astronomy institutes contributing to ESA.
After NIRISS and MIRI commissioning activities are completed, the Webb team will continue to focus on verifying the remaining two modes of its other instruments. NASA’s James Webb Space Telescope, a partnership with ESA (European Space Agency) and CSA, will release its first full-color images and spectroscopic data on July 12, 2022.
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