Successor to the Hubble Space Telescope (HST), the James Webb Space Telescope (JWST) will help us to find out more about the origins of the Universe by observing infrared light from the youngest galaxies and possibly the first stars. It will show us in detail how stars and planetary systems form and will also allow us to study planets both in our Solar System and those orbiting around other stars.
The James Webb Space Telescope (JWST) is designed to expand the scientific success of Hubble. Being a 'cool' telescope, JWST is designed to operate at very low temperatures (around -230° C). This will give us an unprecedented view of the Universe at near and mid-infrared wavelengths and will allow scientists to study a wide variety of celestial objects, ranging from planets in the Solar System to nearby stars, from neighbouring galaxies out to the farthest reaches of the very distant Universe. JWST is required to operate for a minimum of five years, planned for ten.
JWST is very big: 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. All of these characteristics set JWST apart from other existing or planned observatories and will open a new field of scientific discovery.
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 the 6.5-m telescope and the even larger sun-shield of the JWST into a 5 m diameter rocket, described as ‘a bit like designing a ship in a bottle’. As such, JWST will be launched in a folded position and will deploy once in space, during the first three weeks of its travel to its final orbit around the Lagrange point 2 (L2).
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. NIRSpec will also be used to study the properties and composition of 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. It will also be used to study extra-solar planets.
The fourth instrument is the near-infrared imager and slitless spectrograph (NIRISS). In its slitless spectroscopy mode, it will allow spectra to be obtained of all the objects within its large field of view, and it has been specially designed to facilitate the recovery of these spectra even when they overlap. It also includes a spectroscopic observing mode optimized for exoplanet spectroscopy, but is expected to contribute to all of the mission’s science themes.
To enable the stable pointing at the milli-arcsecond level required by JWST to achieve its scientific objectives, JWST is also equipped with a Fine Guidance Sensor (FGS).
JWST will be launched on an Ariane 5 from ESA’s Spaceport in Kourou; launch is currently scheduled on 30 March 2021. The spacecraft must be cooled down to approximately -230ºC so that the instruments’ own infrared emission cannot overwhelm the faint signals from observed objects. It will therefore orbit Lagrange Point 2, 1.5 million km beyond Earth’s orbit, away from the Sun. This special location keeps pace with Earth as we orbit the Sun. It offers a clearer view of the cosmos than an orbit around Earth, which would result in the spacecraft passing in and out of Earth's shadow and causing it to heat up and cool down, distorting its view. Free from this restriction and far away from the heat radiated by Earth, L2 provides a much more stable viewpoint.
The James Webb Space Telescope was formerly known as the Next Generation Space Telescope (NGST) and 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 NASA, ESA and the Canadian Space Agency.