What is JWST?

The James Webb Space Telescope (JWST, or sometimes Webb) is a large space telescope that was successfully launched on December 25 2021 and is currently being deployed. After completion of its 6 month cool down and on-orbit check out, it will commence observations at near- and mid-infrared wavelengths (~0.7–27μm). In many respects, JWST is the successor to the successful Hubble Space Telescope (HST), which has instruments that are sensitive to wavelengths of ~0.1–1.7μm, although it is expected that the two space telescopes will be operational simultaneously into the mid-2020s. The primary mirror of the JWST is composed of 18 hexagonal mirror segments with a combined diameter of ~6.5 m. This gives JWST a much larger light collecting power than HST, and the ability to produce images as sharp as HST's at ~2.7 times longer wavelengths.

Such long wavelengths are needed to directly observe the starlight of the first galaxies that formed in the Universe, dimmed and stretched by the cosmic expansion to magnitudes too faint and wavelengths too long to be detected with HST. They are also needed to peer through the dusty environments of the birth sites of stars and planets in our own Galaxy and its cosmic neighbors, as well as to directly image exoplanets and measure the composition of their atmospheres close in to their parent stars in our Galactic neighborhood.

The JWST was launched atop an Ariane 5 rocket from French Guiana and will operate in an orbit around the second Earth-Sun Lagrange point (L2), at a distance of ~1.5 million kilometers (almost a million miles) from the Earth. Its tennis court sized sunshield will keep the telescope and instruments perpetually in the shade, so they can passively cool to ~35–40K, and remain at a stable temperature for long periods of time. Such ultra-low (cryogenic) temperatures are necessary to prevent blinding the sensitive detectors by the glow of the telescope and instruments themselves at wavelengths longer than ~4μm. Passive cooling is necessary to extend the operational life-time of the telescope to 10–15 years — much longer than prior infrared missions that relied on cryogens for cooling.

The JWST was developed by an international partnership led by the National Aeronautics and Space Administration (NASA), with significant contributions from the European (ESA) and Canadian (CSA) Space Agencies. The project originated in 1996 as the Next Generation Space Telescope (NGST), but was renamed in 2002 after NASA's second administrator James E. Webb, who played a key role in the Apollo program and established scientific research as a core NASA activity.