The James Webb Space Telescope (JWST) is designed to expand the scientific success of the Hubble Space Telescope. Being a 'cool' telescope, JWST is designed to operate at very low temperatures (around -230° C). This will give it an unprecedented view of the Universe at infrared wavelengths and will allow it to observe a wide variety of celestial objects, ranging from planets in the Solar System to nearby stars, from neighbouring galaxies to galaxy clusters, and out to the farthest reaches of the very distant Universe. It is planned to operate for five years, possibly ten.
JWST is also very big, as its primary mirror has an area seven times larger than that of Hubble, which will make it much more sensitive. JWST will combine superb image quality, a large field of view, and a low level of background light with a highly stable environment away from the turbulence of the Earth's atmosphere that blurs images collected on the ground. All of these characteristics set JWST apart from other existing or planned observatories and will be instrumental in the search for the faintest stars and galaxies.
JWST will be launched on board an Ariane V ECA rocket from the European Spaceport of Kourou, in French Guiana. One technical challenge is trying to pack a 6.5-m spacecraft into a 5 m diameter rocket, described as ‘a bit like designing a ship in a bottle’. Besides the telescope mirrors, the spacecraft, and the large sun shield, the JWST observatory has four scientific instruments mounted behind the telescope itself:
The Near Infrared Camera (NIRCam) is mainly designed for imaging studies and the detection of faint objects. The topics for which NIRCam will be invaluable include the search for the first stars, star clusters and galaxy cores that formed after the Big Bang; the study of far distant galaxies seen in the process of formation or merging; the detection of light distortion due to dark matter; the discovery of supernovae in remote galaxies; studies of the stellar population in nearby galaxies, of young stars in the Milky Way and of Kuiper Belt objects in our Solar System.
The Near-Infrared Spectrograph (NIRSpec) will obtain spectra of more than 100 galaxies or stars simultaneously and is sensitive over a wavelength range that matches the peak emission from the most distant galaxies. The key scientific objectives of NIRSpec are the study of star formation and chemical abundances of young distant galaxies; tracing the creation of the chemical elements back in time; exploring the history of the intergalactic medium, i.e. the gaseous material that fills the vast volumes of space between the galaxies; characterising the atmospheres of extra-solar planets.
The Mid-Infrared Camera and Spectrograph (MIRI) is an essential tool for studying extremely old and distant stellar populations; regions of intense star formation that are hidden behind thick layers of obscuring dust; hydrogen emission from previously unthinkable distances; the physics of protostars; Kuiper Belt objects and faint comets.
The Fine Guidance Sensor (FGS) will provide high-precision signals to the observatory to enable stable pointing at the milli-arcsecond level. It will also support star field identification via correlation with a star catalogue as well as spatial and radiometric calibrations.
JWST must be cooled so that the instruments’ own infrared emission cannot overwhelm the faint signals from observed objects. The JWST orbit will be 1.5 million km away from Earth, at Lagrange Point 2 (L2), so it must be extremely reliable, even though it is using new and innovative technology, because it will be too far away for astronauts to service it.
The James Webb Space Telescope was formerly known as the Next Generation Space Telescope (NGST). Due for launch on an Ariane 5, it will follow in HST’s footsteps. ESA has participated actively in both missions from the very beginning, bringing huge scientific benefits to European astronomers, while promoting competitiveness and cross-border collaboration within European science as a whole. NASA and ESA, joined by the Canadian Space Agency, have collaborated on JWST since 1997.
JWST is a partnership between ESA, NASA and the Canadian Space Agency.
Last update: 8 February 2013