James Webb Space Telescope
The largest and most powerful space telescope ever launched — a time machine capable of peering back 13.5 billion years to observe the first galaxies born after the big-bang. Successor to Hubble, operating in near- and mid-infrared to penetrate dust clouds opaque to visible light. Referenced in dark-matter and dark-energy as the primary current observatory for cosmological observation.
Joint mission of NASA, ESA, and CSA. Contributed to by 14 countries, 29 US states. Named after James E. Webb, NASA administrator 1961–1968 — considered one of the most consequential government science administrators in US history.
Key Specifications
| Parameter | Value |
|---|---|
| Launch | Dec 25, 2021, Ariane 5, Kourou, French Guiana |
| Orbit | L2 Lagrange point, 1.5 million km from Earth (orbits the Sun, not Earth) |
| Primary mirror | 6.5 m diameter, 18 hexagonal beryllium segments coated in gold |
| Mirror area | ~25 m² (vs. Hubble's 4.5 m²) — ~100× more light-collecting power |
| Sunshield | 5-layer, tennis-court sized; attenuates solar heat by >1,000,000× |
| Hot side | ~85°C |
| Cold side | ~−233°C |
| MIRI temperature | 7 K (coldest instrument; requires active cryocooler) |
| Wavelength | 0.6–28 µm (near-infrared to mid-infrared) |
Science Themes
Early Universe — Observing the first stars and galaxies that formed ~100–400 million years after the Big Bang; studying reionization. Webb's infrared sensitivity reveals objects whose light has been redshifted by cosmic expansion beyond visible wavelengths.
Galaxy Assembly — Tracing how galaxies form, evolve, merge, and grow their dark-matter halos across cosmic time.
Star and Planet Formation — Imaging stellar nurseries and protoplanetary disks through dust clouds that block visible light; directly imaging exoplanet atmospheres for biosignature searches.
Solar System — Detailed study of planets, moons, and small bodies including characterizing atmospheric chemistry.
Engineering Innovations
Folded mirror — The 6.5 m primary mirror was too large to fit in any rocket fairing; it was designed to fold origami-style for launch and unfold in space — an intricate deployment sequence with 344 single-point-of-failure mechanisms, all of which worked.
Sunshield — Five layers of Kapton film, each as thin as a human hair, reduce the temperature from hot side (+85°C) to the cold side (−233°C) needed for infrared sensitivity. Without this, Earth's heat would drown out the faint infrared from the early universe.
NIRSpec microshutters — 250,000 programmable microshutters allow simultaneous spectroscopy of up to 100 astronomical objects; a unique capability enabling high-efficiency survey science.
L2 Orbit
Unlike Hubble (Earth orbit), Webb orbits the Sun–Earth L2 Lagrange point — 1.5 million km beyond Earth in the direction away from the Sun. This keeps Earth, Moon, and Sun always on the same side, allowing the sunshield to block all three simultaneously and maintaining a stable thermal environment. Webb cannot be serviced by astronauts.
First Science
Webb's first science images released July 2022 included the deepest infrared image of the universe ever taken (Webb's First Deep Field — galaxy cluster SMACS 0723), a spectrum of an exoplanet atmosphere, and stunning imagery of the Carina Nebula and Stephan's Quintet. As of 2026 Webb continues full science operations, producing multiple major discoveries per month across all four science themes.