Webb has a suite of four powerful instruments that will investigate the cosmos. They are located in the Integrated Science Instrument Module, behind the primary mirror. MIRI is the only instrument on the telescope that is capable of operating at mid-infrared wavelengths. It will 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 is a versatile instrument offering a wide set of modes: imaging, coronagraphy and different flavours of spectroscopy. To observe the cosmos in the mid-infrared, MIRI must be kept more than 30 degrees cooler than the other instruments in the Webb observatory. This is accomplished by the use of an innovative cooling system known as a cryocooler, which will act as an extra refrigerator for the MIRI instrument. MIRI will provide imaging, coronagraphy and spectroscopy over the 5 µm ̶ 28 µm wavelength range. It will operate at –266°C (compared with –233°C for the rest of the observatory). This is barely seven degrees above absolute zero, the lowest temperature possible according to the laws of physics.

Webb has a suite of four powerful instruments that will investigate the cosmos. They are located in the Integrated Science Instrument Module, behind the primary mirror. A spectrograph is used to disperse light from an object into its different wavelengths, forming a spectrum, similarly to how a rainbow is formed when light passes through a prism. Any object that absorbs or emits light can be studied with a spectrograph to determine characteristics such as its temperature, density, chemical composition, and velocity. Webb’s images will tell us what something looks like, while the spectrograph data tell us what it is and what it’s made of. The NIRSpec instrument is the workhorse near-infrared spectrograph on board Webb, and is provided entirely by ESA. The primary goal of NIRSpec is to enable large spectroscopic surveys of astronomical objects such as stars or distant galaxies. This is made possible by its powerful multi-object spectroscopy mode, which makes use of microshutters. This mode is capable of obtaining spectra of up to nearly 200 objects simultaneously, over a 3.6×3.4 arcminute field of view – the first time this capability has been provided from space. This mode makes for very efficient use of Webb’s valuable observing time. An arcminute is a unit of angular measurement equal to one sixtieth of one degree and is used in astronomy to communicateangles. For example, the angular diameter of the Moon is around 30 arcminutes. NIRSpec also offers integral-field and fixed-slit spectroscopy viewing modes that will allow detailed studies of individual astronomical objects. [NIRSpec Light path graphic - to be added later once we have it] Caption: This figure shows the path followed by light from an astronomical object as it travels through the NIRSpec components and onto the detector. Six filter and grating combinations provide high-resolution and medium-resolution spectroscopy over the wavelength range 0.7 µm – 5.2 µm. The prism yields lower-resolution spectroscopy over the range 0.6 µm – 5.3 µm

Webb’s NIRCam is the observatory’s primary camera, and will simultaneously image the cosmos in two different infrared ranges. Taking advantage of Webb’s exquisite image quality and large primary mirror, the instrument will acquire some of the deepest (i.e. farthest away) near-infrared images ever obtained, detecting light from the first stars and galaxies. NIRCam also has coronagraphic and spectroscopic capabilities, which will, for example, be used to characterise exoplanets. NIRCam will also be the primary tool for alignment of the telescope. It was provided by the University of Arizona.

NIRISS is an innovative instrument that will support operations in three observing modes. It has a camera that will be usable in parallel with the NIRCam camera to provide additional imaging capabilities for Webb. It features a slitless spectrograph, where all the light falling on the camera will be dispersed into its spectrum. Unlike in an ordinary spectrograph, the light source in a slitless spectrograph is not a narrow slit. NIRISS also offers a spectroscopic mode that is specially designed for exoplanet characterisation using transit spectroscopy, a technique that allows Webb to study the chemical composition of an exoplanet’s atmosphere when it passes in front of its host star. The instrument’s accompanying fine guidance sensor will allow Webb to remain steadily locked on or pointed, with very high precision, at a specific celestial target – even a moving one. This high precision means that it can obtain high-resolution images and spectra. With NIRISS, astronomers will study whether or not the spectra of distant planets show lines characteristic of molecules such as water, carbon dioxide, methane and oxygen in their atmospheres – key to the search for life-friendly conditions. NIRISS was provided by the Canadian Space Agency