The Mid-Infrared Instrument (MIRI) is one of Webb’s four scientific instruments. MIRI provides imaging and spectroscopy capabilities in the mid-infrared. As the only mid-infrared instrument, astronomers rely on MIRI to study cooler objects like debris disks, which emit most of their light in the mid-infrared, and extremely distant galaxies whose light has been shifted into the mid-infrared over time. MIRI was developed through a collaboration between the European Consortium (EC) and the Jet Propulsion Laboratory (JPL).
MIRI Components Cameras capture two-dimensional images of regions of space. Spectrographs spread light out into a spectrum so that the brightness of each individual wavelength can be measured. Coronagraphs are opaque disks used to block the bright light of stars in order to detect the much fainter light of planets and debris disks orbiting the star. An integral field unit (IFU) is a combination of camera and spectrograph used to capture and map spectra across a field of view in order to understand variation over space.
MIRI Wavelength Range MIRI is designed to capture light ranging in wavelength from 4.9 to 28.8 microns (mid-infrared).
MIRI Field of View An instrument’s field of view is the amount of sky that it can observe at any given point in time. (The actual area that can be observed depends on the distance of the object being observed.) In this graphic, a Hubble Space Telescope image of the Whirlpool Galaxy (M51) is shown for scale. The image covers an area of 9.6 × 6.6 arcminutes. (The full Moon has a diameter of about 31 arcminutes across the sky.) MIRI’s main field of view is 1.2 × 1.9 arcminutes. The fields of view of its coronagraphs and IFU are smaller.
MIRI Imaging Modes Standard Imaging is the equivalent to basic digital photography and involves capturing pictures of a wide variety of objects and materials in space that emit or reflect infrared light. Coronagraphic Imaging (sometimes called high-contrast imaging) involves using a coronagraph to block the light of a star in order to reveal the much dimmer light of nearby objects, such as exoplanets and debris disks. Time-Series Imaging involves capturing a series of images at regular intervals in order to measure changes over time. Time-series can be used to track changes in the brightness of a star or can be combined with coronagraphic imaging to track the motion of a planet.
MIRI Spectroscopy Modes Single-Object Slitless Spectroscopy involves capturing the spectrum of a single bright object like a star in a field of view. Slitted Spectroscopy provides the ability to capture the spectrum of a single object—a single star, a single exoplanet, or a single distant galaxy—in a wide field of view. Single slit spectroscopy is also used to analyze the spectrum of a small area of an object that is large in the field of view, such as a galaxy or planet. Integral Field Unit Spectroscopy (IFU) involves a combination of imaging and spectroscopy. During an IFU observation, the instrument captures an image of the field of view along with individual spectra of each pixel in the field of view. IFU observations allow astronomers to investigate how properties—such as composition, temperature, and motion—vary between different objects such as stars in a crowded star field, or from place to place over a large region of space such as a galaxy or nebula. Time-Series Spectroscopy involves capturing the spectrum of an object or region of space at regular intervals in order to observe how the spectrum changes over time. Time-series spectroscopy is used to study planets as they transit their stars.
Credits
Illustration
NASA, ESA, Andi James (STScI)
