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James Webb Space Telescope

Webb's 6.5 m mirror sees in infrared from about 1.5 million km away, revealing the earliest galaxies and the atmospheres of exoplanets.

Infrared observatory at L2

Missions
  • Last reviewed 10 Oct 2026
  • 6 sources

At a glance

James Webb Space Telescope at a glance, with sources
MeasureValueSource
OrbitSun–Earth L2, about 1.5 million km from EarthNASA Science: Webb (opens in a new tab)NASA Science: Webb (opens in a new tab)
Most distant galaxy confirmedMoM-z14 at z = 14.44, about 280 million years after the Big Bangas of Oct 2026NASA Science: Webb pushes boundaries of observable universe (opens in a new tab)NASA Science: Webb pushes boundaries of observable universe (opens in a new tab)
First clear exoplanet CO₂WASP-39 b (announced Aug 2022)JWST Transiting Exoplanet Community ERS Team 2023, Nature 614:649 (arXiv) (opens in a new tab)JWST Transiting Exoplanet Community ERS Team 2023, Nature 614:649 (arXiv) (opens in a new tab)
Rocky-planet testTRAPPIST-1 b and c lack thick CO₂ atmospheresGillon et al. 2026, Nature Astronomy (opens in a new tab)Gillon et al. 2026, Nature Astronomy (opens in a new tab)
Launched25 Dec 2021 on an Ariane 5 from Kourou, French GuianaESA: Webb factsheet (opens in a new tab)ESA: Webb factsheet (opens in a new tab)
Primary mirror6.5 m across, 18 hexagonal beryllium segments coated in goldThe gold layer is about 100 nanometres thick.NASA Science: Webb telescope overview (opens in a new tab)NASA Science: Webb telescope overview (opens in a new tab)
SunshieldFive layers, about 22 × 12 mRoughly the size of a tennis court.ESA: Webb factsheet (opens in a new tab)ESA: Webb factsheet (opens in a new tab)
Operating temperatureAbout −233 °C; the MIRI instrument about −266 °CESA: Webb factsheet (opens in a new tab)ESA: Webb factsheet (opens in a new tab)
Wavelength rangeAbout 0.6 to 28 micrometresHubble covers about 0.1 to 2.5 micrometres.ESA: Webb factsheet (opens in a new tab)ESA: Webb factsheet (opens in a new tab)

Key points

  • Sees the universe 280 million years after the Big Bang
  • Measures exoplanet atmospheres
  • Parked 1.5 million km from Earth

Why infrared

Light from the first galaxies has been stretched by cosmic expansion into infrared. Dust that hides newborn stars is also transparent at those wavelengths.

A telescope launched folded

No rocket fairing could hold Webb fully open, so the mirror wings and the sunshield flew folded, like a piece of origami. In the month it took to reach L2, where it arrived on 24 January 2022, the shield unfurled and the mirror locked into shape. Engineers then spent months nudging the 18 segments until they behaved as one smooth surface. The first science images came out in July 2022, once commissioning was complete.

Keeping the optics cold

A warm infrared telescope is blinded by its own heat. The sunshield keeps the Sun, Earth and Moon, which all sit on the same side at L2, off the optics, so the cold side settles near −233 °C. The mid-infrared camera, MIRI, needs extra help: a cryocooler takes it down to about −266 °C, only seven degrees above absolute zero.

Webb and Hubble together

Webb does not replace Hubble. Hubble's view runs from ultraviolet into the near infrared, while Webb starts at the red end of visible light and reaches deep into the mid infrared, with about six times Hubble's light-collecting area. Astronomers often point both at the same object: Hubble shows the hot young stars, Webb the dust and gas around them.

An international observatory

NASA leads Webb with ESA and the Canadian Space Agency. Europe supplied the launch, the NIRSpec spectrograph, the optical bench of MIRI and part of the operations staff. In return, European scientists receive at least 15% of the observing time. Space Telescope Science Institute in Baltimore runs the observatory day to day.

What we still don't know

Why bright galaxies appeared so early, and whether any rocky planet around a red dwarf keeps an atmosphere.

Missions

  1. 2021–

    James Webb Space Telescope

    NASA / ESA / CSAActive

    Infrared observatory at Sun–Earth L2, about 1.5 million km from Earth.

    Mission page (opens in a new tab)

Sources

  1. NASA Science: Webb (opens in a new tab)
  2. NASA Science: Webb pushes boundaries of observable universe (opens in a new tab)
  3. JWST Transiting Exoplanet Community ERS Team 2023, Nature 614:649 (arXiv) (opens in a new tab)
  4. Gillon et al. 2026, Nature Astronomy (opens in a new tab)
  5. ESA: Webb factsheet (opens in a new tab)
  6. NASA Science: Webb telescope overview (opens in a new tab)

Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.