Webb's versatile instruments will work across a wide range of visible-red through mid-infrared colors. Each instrument is uniquely designed to look at particular details. In addition to filters that isolate particular color ranges, the instruments contain a variety of special tools designed to maximize the scientific knowledge gleaned from every observation.
Webb will have a total of four science instruments: the Near-Infrared Camera, Near-Infrared Spectrograph, Mid-Infrared Instrument, and the Fine Guidance Sensor/Near-Infrared Imager and Slitless Spectrograph. Webb's instruments are housed in the Integrated Science Instrument Module, a structure that functions as the heart of the Webb Telescope.
NEAR INFRARED CAMERA (NIRCam)
Webb's Near Infrared Camera (NIRCam) will help scientists answer questions about the early phases of star and galaxy formation. It will yield data about the shapes and colors of faraway, young galaxies, allowing astronomers to determine how galaxies change over time. In addition, NIRCam will help astronomers to determine the ages of stars in nearby galaxies.
Astronomers plan to use NIRCam to create an ultra-deep survey of the distant universe — similar to the famous Hubble deep fields, but in infrared — designed to find some of the most distant objects in space. NIRCam will take a series of pictures using filters that pick up different wavelengths, and use the changes in brightness it detects between these images to estimate the redshifts of the distant galaxies. Redshifting is the stretching of light toward longer wavelengths that occurs as light travels through the expanding universe, and can be used to gauge distance. These NIRCam observations will probe 13 billion years into the universe's past, and reveal more information about the characteristics of the first objects to appear in the universe.
NIRCam is equipped with coronagraphs, instruments that allow astronomers to take pictures of very faint objects around a central bright object, such as a star. NIRCam's coronagraphs work by blocking a brighter object's light, making it possible to view the dimmer object nearby — just like shielding the sun from your eyes with an upraised hand can allow you to focus on the view in front of you. Using coronagraphs, astronomers hope to determine the characteristics of planets orbiting nearby stars.
NIRCam also will help ensure the perfect alignment and shape of Webb's primary mirror segments. NIRCam is equipped with special optics that can capture the image of a single, bright star and deliberately place it out of focus, spreading out its light. Astronomers then analyze that out-of-focus image, looking for patterns that are consistent with all the mirrors being in alignment, or indicative of a problem.
NIRCam will be Webb's primary imager at wavelengths 0.6-5 microns.
NIRCam is being built by the University of Arizona and Lockheed Martin. For more information, visit NASA's NIRCam page.
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NEAR INFRARED SPECTROGRAPH (NIRSpec)
The Near-Infrared Spectrograph (NIRSpec) is the Webb telescope's primary spectrograph, unraveling the light of faint objects and their components. A spectrograph is an instrument that spreads light into its various wavelengths, allowing them to be analyzed. This helps scientists determine which elements the object contains, the velocity of various parts of the object, and its redshift.
NIRSpec will be used to measure accurate redshifts to distant galaxies and to measure their chemical evolution. NIRSpec will also study how gas and dust clump together to form new stars and planets.
A unique capability of NIRSpec will be its ability to study the light of more than 100 objects at once. This is made possible by the Micro Shutter Assembly (MSA). The MSA consist of arrays of thousands and thousands of tiny shutters that can be opened in the pattern of objects on the sky, allowing only the light from objects of interest into the instrument. This will allow NIRSpec to perform a spectroscopic survey of many distant galaxies at a variety of ages. The observations can reveal the star formation rate in each galaxy. They will also help measure the chemistry of galaxies, and study how stars change with a galaxy's age, answering questions like: what kinds of stars are forming in these galaxies, when does star formation stop, and what causes it to stop. With this information, scientists can determine how galaxies over time take on the properties we see in them today.
NIRSpec will be the Webb's primary spectrograph at wavelengths 0.6-5 microns.
NIRSpec is being built by the European Space Agency, with the detectors and multi-shutter array provided by Goddard Space Flight Center/NASA. For more information, visit NASA's NIRSpec page.
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MIRI's sensitive camera and spectrograph will be able to see far away in time and space, back to a time when galaxies were young. MIRI is the only instrument on Webb that can see objects like these early galaxies, which appear in long mid-infrared wavelengths.
Because the universe is expanding, the light from stars similar to our Sun in these galaxies has been redshifted to mid-infrared wavelengths. MIRI will be able to detect these.
MIRI will play a large role in Webb's mission to understand faraway galaxy formation and evolution, the physical process of star formation, and the creation of the heavier chemical elements, such as carbon, oxygen, and iron. But even more excitingly, MIRI will be used to study the origins of the building blocks of life. In the cold regions where stars are forming, gas and dust are present. Both leave fingerprints in the spectra of forming stars, revealing how that gas and dust interacted to create stars. These materials are also the building blocks of the planetary systems being created around the young stars. These observations will reveal the origin of water and organic materials in young planetary systems.
MIRI is also equipped with a complex coronagraph, which blocks the glare of nearby bright objects to allow clear observations of faint objects.
MIRI will operate in the 5- to 28-micron wavelength range.
MIRI was built by the MIRI Consortium, a group that consists of scientists and engineers from European countries, a team from the Jet Propulsion Lab in California, and scientists from several U.S. institutions. For more information, visit NASA's MIRI page.
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FINE GUIDANCE SENSORS/Near-Infrared Imager and Slitless Spectrograph (FGS/NIRISS)
Two instruments — the Fine Guidance Sensor (FGS) and the Near-Infrared Imager and Slitless Spectrograph (NIRISS) — are packaged together, but have separate purposes. The FGS is the guide camera for the observatory, which helps point the telescope, while NIRISS is a specialized science instrument.
Like NIRSpec, NIRISS is a spectrograph, designed to break light apart into separate wavelengths for analysis. NIRISS will be able to take extremely precise spectra of bright objects, capturing more light than NIRSpec. NIRISS will also be used to detect faint objects, like planets, that are very near their parent stars. Since it doesn’t use a coronograph, it will use a special masking technique to capture objects that have very close proximities. And like NIRCam, NIRISS can make its observations through a variety of specially selected filters.
NIRISS will tackle a diverse range of science topics. It will discover distant galaxies in the universe and make detailed maps of crowded regions such as the centers of galaxies where quasars reside. Observations with NIRISS will examine the atmospheric makeup of potentially habitable, Earth-like planets found around nearby low-mass stars. Differences between spectra obtained from the star and planet, or the star only (when the planet is behind the star) will reveal the makeup and structure of the planet’s atmosphere. Observations like these can determine whether the planet’s atmosphere contains the organic molecules required to support life.
The FGS helps point the telescope in two ways. First, at the start of an observation, it takes pictures to identify where the telescope is pointing. Then, it finds a “guide star” that is close to the field of view containing the object to be studied. As long as the guide star stays in exactly the same position in the field of the FGS, the telescope will point at the target of scientific interest, which can be examined by one of the science instruments.
The telescope tends to wander by small amounts, since it is orbiting in space and affected by solar radiation, its own moving parts, the sloshing of its propellant, and other forces. To track these changes, the FGS measures the position of the guide star 16 times per second and relays these measurements to the onboard computer. When the computer detects small drifts, it orders the telescope to correct itself in order to keep its positioning relative to the guide star.
The FGS and NIRISS are provided by the Canadian Space Agency. For more information, visit NASA's FGS/NIRISS page.