MIRI (Mid-Infrared Instrument)

MIRI, or Mid-Infrared Instrument, is an instrument on the planned James Webb Space Telescope. MIRI is a camera and a spectrograph that observes mid infrared radiation from 5 microns to 28 microns. It also has coronagraphs, especially for observing exoplanets.

Whereas most of the other instruments on Webb can see from the start of Near-infrared, or even as short as orange visible light, MIRI can see longer wavelength light where the other instruments leave off. MIRI uses silicon arrays doped with Arsenic to make observations at these wavelengths. The imager is designed for wide views but the spectrograph has a smaller view. Because it views the longer wavelengths it needs to be cooler than the other instruments (see Infrared astronomy), and it has an additional cooling system. The cooling system for MIRI includes a Pulse Tube precooler and a Joule-Thomson Loop heat exchanger. This allows MIRI to be cooled down to 7 kelvin during operations in space.

The spectrograph can observe wavelengths between 4.6 and 28.6 microns, and it has four separate channels, each with its own gratings and image slicers. The field of view of the spectrograph is 3.5 by 3.5 arcseconds.

The imager has a plate scale of 0.11 arcseconds/pixel and a field of view of 1.7 by 1.3 arcmin. The imaging channel has ten filters available and the detectors are made of arsenic-doped silicon (Si:As). The detectors have a resolution of 1024x1024 pixels, and they are called Focal Plane Modules or FPMs.

During 2013 and finishing in January 2014, MIRI was integrated into the Integrated Science Instrument Module (ISIM). MIRI successfully passed Cryo Vac 1 and Cryo Vac 2 tests as part of ISIM in the 2010s. MIRI was developed by an international consortium.

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