The Mid-InfraRed Instrument (MIRI) of the James Webb Space Telescope (Webb) sees light in the mid-infrared region of the electromagnetic spectrum, at wavelengths that are longer than our eyes can see.

To support the whole range of Webb’s science goals, from observing our own Solar System and other planetary systems, to studying the early Universe, MIRI allows scientists to use multiple observing techniques: imaging, spectroscopy and coronagraphy.

To pack all these modes in a single instrument, engineers have designed an intricate optical system in which light coming from Webb’s telescope follows a complex 3D path before finally reaching MIRI’s detectors.

This artist’s rendering shows this path for MIRI’s imaging mode, which provides imaging and coronagraphy capabilities. It also contains a simple spectrograph. We first take a look at its mechanical structure with its three protruding pairs of carbon fibre struts that will attach it to Webb’s instrument compartment at the back of the telescope.

The pick-off mirror, acting like a periscope, receives the light from the telescope, shown in deep blue, and directs it into MIRI’s imaging module. Inside the instrument, a system of mirrors reformats the light beam and redirects it till it reaches a filter wheel where the desired range of mid-infrared wavelengths is selected from a set of 18 different filters each with its own specific function (the beam takes a light blue colour in the animation).

Lastly, another set of mirrors takes the light beam coming out of the filter wheel and recreates the image of the sky on MIRI’s detectors.

MIRI was developed as a partnership between Europe and the USA. The main partners are ESA, a consortium of nationally funded European Institutes, the Jet Propulsion Laboratory (JPL), and Goddard Space Flight Center (GSFC). The European Consortium institutes built the MIRI imager, spectrographs and coronagraph to ESA’s standards, and the detectors and dedicated cooler systems are provided by JPL. 

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