The JWST Mid-Infrared Instrument (MIRI) provides imaging and spectroscopic observing modes from ~5 to 28μm.  

The JWST Mid-Infrared Instrument (MIRI) provides imaging and spectroscopic observing modes from 4.9 to 27.9 μm. These wavelengths can be utilized for studies including, but not limited to: direct imaging of young warm exoplanets and spectroscopy of their atmospheres; identification and characterization of the first galaxies at redshifts z > 7; and analysis of warm dust and molecular gas in young stars and proto-planetary disks.

To achieve these goals MIRI offers a very broad range of observing modes, including: 

• imaging 
• low-resolution fixed slit and slitless spectroscopy
• medium-resolution integral field unit (IFU) spectroscopy
• coronagraphy 

Observational capabilities

MIRI offers 4 different observing modes, including (1) imaging with 9 photometric bands, (2) coronagraphic imaging with 4 different filters, (3) low-resolution spectroscopy with a slit or slitless configuration, and (4) medium-resolution spectroscopy with 4 different IFUs. Each mode has its own template in the Astronomer's Proposal Tool (APT). Note that MIRI can also be used effectively for parallel observations with other instruments.

Table 1. Properties of MIRI observing modes

Optical elements

Imager

The major optical elements in the MIRI imager include an 18-station filter wheel, coronagraphic masks, and a single 1k × 1k pixel mid-infrared detector:

• Filter wheel—the 18-station filter wheel includes imaging filters, LRS prism, and coronagraphic filters.
   
• Coronagraphic masks—in addition to a classical Lyot coronagraph at the telescope focal plane, MIRI incorporates the 4-quadrant phase mask coronagraph technology (4QPM; Rouan et al. 2000) to provide the smallest possible inner working angle (IWA) of ~1λ/D at 10–16 μm.
   
• Slit—in addition to the coronagraphic masks, the LRS slit is also located at the telescope focal plane.
   
• Detectors—in contrast to other JWST instruments, which use HgCdTe infrared detector arrays, MIRI uses 3 arsenic-doped silicon (Si:As) IBC arrays, each with 1k × 1k pixels. The MIRI detectors were developed specifically for JWST sensitivity requirements; MIRI, being most sensitive to thermal background of all the JWST instruments, is also the coldest instrument, actively cooled to its operating temperature of 7 K by a cryocooler. Since the cryocooler uses a 2-stage closed-cycle design, there is no expendable cryogen.

Medium-resolution spectrometer (MRS)

The major optical elements in the MRS include 2 gratings/dichroic wheels and 4 integral field units (IFUs). The MRS also has 2 mid-infrared detectors of the same type used in the imager.

Sensitivity and performance

Wright et al (2023) summarizes the in-flight performance of MIRI as measured during JWST commissioning; for pre-launch estimates, Glasse et al. (2015) provides a good overview. The instrument's performance is continually being monitored and updated over the course of the mission, so observers preparing MIRI proposals should always use the JWST Exposure Time Calculator (ETC) to obtain detailed performance estimates. Up-to-date information on the use and applicability of the ETC can be found on the ETC website and in the ETC Documentation.

Figure 7. MIRI sensitivity plot for various instrument modes

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Data calibration and analysis

Information about calibration is available in the article JWST Calibration Status; links in the article point to content about absolute astrometric, flux, and wavelength calibration, as well as information on calibration reference files.

Details about the data can be found in the JWST Science Data Overview article. The JWST pipeline is described in JWST Science Calibration Pipeline and some information about post-pipeline processing can be found at JWST Post-Pipeline Data Analysis.

References

Glasse, A., et al. 2015, PASP, 127, 953
The Mid-Infrared Instrument for the James Webb Space Telescope, IX: Predicted Sensitivity

Rouan, D., et al. 2000, PASP, 112, 1479
The Four-Quadrant Phase-Mask Coronagraph. I. Principle

Wright, G.S. et al., 2023, PASP, 135 1046
The Mid-infrared Instrument for JWST and Its In-flight Performance

Additional MIRI links and documents

Papers

Peer-reviewed and conference papers are listed on the MIRI Technical Library page. They are also collected in an ADS Public Library, from which you can generate convenient citation links. 

External MIRI websites

STScI MIRI Website

UK Astronomy Technology Centre; The Royal Observatory, Edinburgh MIRI Site

NASA MIRI Site 

European Space Agency (ESA) MIRI Site

Lectures

JWST Community Lecture Series - The Mid-Infrared Instrument (MIRI) for JWST (G. Rieke)

Acknowledgements

MIRI development was an equal collaboration between European and US partners. 

The MIRI optical system was built by a consortium of European partners from Belgium, Denmark, France, Germany, Ireland, the Netherlands, Spain, Sweden, Switzerland, and the United Kingdom. They were led by Gillian Wright, the European Principal Investigator, and Alistair Glasse, Instrument Scientist.

EADS-Astrium (now Airbus Defence and Space) provided the project office and management. The full instrument test was conducted at Rutherford Appleton Laboratory.

The Jet Propulsion Laboratory (JPL) provided the core instrument flight software, the detector system, including infrared detector arrays obtained from Raytheon Vision Systems, collaborated with Northrop Grumman Aerospace Systems on the cooler development and test, and managed the US effort.

The JPL Instrument Scientist is Michael Ressler and the MIRI Science Team Lead is George Rieke.