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    James Webb Space Telescope (JWST)

    Also known as JWST, Webb, Webb Space Telescope

    The James Webb Space Telescope is a NASA, ESA and CSA infrared observatory with a 6.5-meter mirror, launched on December 25, 2021 and operating 1.5 million km from Earth.[1][2] It has pushed the distance record to a galaxy seen 280 million years after the Big Bang and made exoplanet atmospheres measurable, which has also produced contested claims about possible signs of life.[3][4][5]

    Editor reviewedUpdated Space exploration and astronomySpaceScience
    Key facts

    What it is

    Webb is a joint NASA, ESA and Canadian Space Agency observatory that launched on December 25, 2021.[1] Its primary mirror, about 6.5 meters across, is made of 18 beryllium segments coated with gold, and it observes from 0.6 to 28.5 microns, from red light into the mid-infrared.[2] It works from the Sun-Earth L2 point, about 1.5 million km from Earth, behind a five-layer sunshield, about 21 by 14 meters, that keeps the telescope cold.[1][6] It launched on an Ariane 5 ECA and was designed for a 5- to 10-year mission.[7] It reached L2 on January 24, 2022. Hubble, by contrast, orbits only about 560 km above Earth.[8] The observatory weighed about 6,200 kg at launch and resolves detail down to about 0.1 arcseconds. Its sunshield separates a Sun-facing layer that can reach about 383 K from an outermost cold layer that can drop to 36 K.[9]

    Why infrared

    Light from the most distant galaxies has been stretched into the infrared by the expansion of the universe, and infrared light passes through dust clouds that hide forming stars and planets.[10] NASA groups Webb’s work into four themes: the early universe, how galaxies change over time, the life cycle of stars, and other worlds.[11] The general principles are explained in how space telescopes work.

    The early universe

    One of Webb’s most discussed results concerns how many bright galaxies existed very early. In 2025 a team used Webb’s NIRSpec instrument to confirm the galaxy MoM-z14 at redshift 14.44, about 280 million years after the Big Bang, the most distant example yet of this class.[3] The same survey implied that bright galaxies at that epoch are more than 100 times more common than pre-Webb models predicted.[3]

    Recent results

    Webb keeps finding objects at the edge of what was observable before. In October 2026 a team using Webb reported in Science that it had found the host galaxy of the most distant fast radio burst yet seen, FRB 20240304B. Fast radio bursts are millisecond flashes of radio waves whose origin is still uncertain. The host is a small, star-forming dwarf galaxy seen about 3 billion years after the Big Bang.[12]

    Webb also feeds the main open dispute in cosmology, the Hubble tension. The Chicago-Carnegie Hubble Program used Hubble and Webb distance measurements to get an expansion rate it says fits the standard model without new physics.[13] A 2025 community analysis of many methods found a local value that disagrees with early-universe predictions at 5 to 7 sigma.[14] The arguments are laid out in the Hubble tension debate.

    Exoplanet atmospheres

    Webb can measure what exoplanet atmospheres are made of by splitting starlight that passes through them.[11][15] Its near-infrared spectra of the sub-Neptune K2-18 b detected methane and carbon dioxide, a result independent teams agree on for methane.[16] A 2025 claim of mid-infrared evidence for dimethyl sulfide, a gas produced by life on Earth, proved far more contentious: independent reanalyses found that instrument noise and modelling choices could explain the signal.[4][17][5] The episode is covered in the debate over evidence for life.

    Funding

    Webb is operating, and Congress’s fiscal 2026 appropriation kept NASA science at $7.25 billion, rejecting a proposed 47 percent cut.[18] Webb now works alongside Roman, whose much wider field of view is suited to surveys rather than deep, single-object study.[19]

    Questions readers ask

    Where is the James Webb Space Telescope?

    It orbits the Sun about 1.5 million km from Earth, at the second Lagrange point (L2).[1]

    What is the most distant galaxy Webb has confirmed?

    In 2025 a team confirmed MoM-z14 at redshift 14.44, seen about 280 million years after the Big Bang.[3]

    Did Webb find signs of life on K2-18 b?

    A 2025 study reported tentative evidence for dimethyl sulfide, but several independent reanalyses found no statistically significant signal.[4][5][17]

    Sources

    Each numbered claim is a statement we checked against the sources listed with it. Status shows how well established it is.

    1. [1]

      The James Webb Space Telescope, a joint NASA/ESA/CSA mission, launched on December 25, 2021 and orbits the Sun about 1.5 million km from Earth at the second Lagrange point (L2). confirmedas of 2026-10-10

    2. [2]

      Webb's primary mirror is about 6.5 m across, made of 18 gold-coated beryllium segments, and the telescope observes wavelengths from 0.6 to 28.5 microns. confirmedas of 2026-10-10

    3. [3]

      In 2025 a team used Webb spectroscopy to confirm the galaxy MoM-z14 at redshift 14.44, seen about 280 million years after the Big Bang, and found bright galaxies at that epoch to be more than 100 times more common than pre-Webb models predicted. confirmedas of 2025-05-16

    4. [4]

      In April 2025 a team led by Nikku Madhusudhan reported Webb mid-infrared evidence at 3-sigma significance for dimethyl sulfide and/or dimethyl disulfide, possible biosignature gases, in the atmosphere of the sub-Neptune K2-18 b. confirmedas of 2025-04-16

    5. [5]

      A May 2025 joint reanalysis of all Webb data on K2-18 b found insufficient evidence for DMS or DMDS, with other molecules such as ethane fitting equally well, attributed marginal preferences to limiting the molecules modelled and to sensitivity to small changes between data reductions, and estimated about 25 more MIRI transits would be needed for a decisive test. confirmedas of 2025-05-19

    6. [6]

      Webb uses a five-layer sunshield, about 21 by 14 meters, to block infrared radiation from the Sun, Earth and Moon. confirmedas of 2026-10-10

    7. [7]

      Webb launched on an Ariane 5 ECA rocket and was designed for a mission of 5 to 10 years. confirmedas of 2026-10-10

    8. [8]

      Webb arrived at L2 on January 24, 2022; by comparison, Hubble orbits about 560 km above Earth. confirmedas of 2026-10-10

    9. [9]

      Webb's launch mass was about 6,200 kg, its optical resolution is about 0.1 arcseconds, and its sunshield layers range from a maximum of about 383 K on the Sun-facing layer to as cold as 36 K on the coldest layer. confirmedas of 2026-10-10

    10. [10]

      Webb observes in infrared because light from the earliest galaxies has been stretched (redshifted) into the infrared by cosmic expansion, and infrared light passes through dust that hides forming stars. confirmedas of 2026-10-10

    11. [11]

      NASA groups Webb's science into four themes, the early universe, galaxies over time, the life cycle of stars, and other worlds, including measuring what exoplanet atmospheres are made of. confirmedas of 2026-10-10

    12. [12]

      In October 2026 a team using Webb reported in Science that it had identified the host galaxy of the most distant fast radio burst yet seen, FRB 20240304B, a small star-forming dwarf galaxy seen about 3 billion years after the Big Bang. confirmedas of 2026-10-08

    13. [13]

      The Chicago-Carnegie Hubble Program, using Hubble and JWST tip-of-the-red-giant-branch distances, reported a Hubble constant of 70.39 ± 1.22 (stat) ± 1.33 (sys) ± 0.70 km/s/Mpc, which it says is consistent with Lambda-CDM without new physics. confirmedas of 2026-10-10

    14. [14]

      The H0DN local value differs by 7.1 sigma from flat Lambda-CDM fitted to Planck, SPT and ACT CMB data, and by 5.0 sigma from a combination of Big Bang nucleosynthesis and DESI BAO data. confirmedas of 2026-10-10

    15. [15]

      Light passing through or coming from an exoplanet's atmosphere can be split into a spectrum whose absorption bands reveal which molecules are present. confirmedas of 2026-10-10

    16. [16]

      Earlier Webb near-infrared spectra of K2-18 b detected methane and carbon dioxide, and independent reanalyses agree on methane. confirmedas of 2025-09-03

    17. [17]

      A 2025 analysis applying the astrobiology standards-of-evidence framework concluded that instrumental red noise affects the K2-18 b mid-infrared data and that there is not yet statistically significant evidence of biosignatures. confirmedas of 2025-09-03

    18. [18]

      Congress's fiscal 2026 appropriations bill, passed in January 2026, gave NASA about $24.4 billion, including $7.25 billion for science, rejecting a proposed 47 percent cut to science. confirmedas of 2026-01-16

    19. [19]

      Roman has a field of view at least 100 times larger than Hubble's, carries a Wide Field Instrument and a Coronagraph, and is designed to address dark energy, exoplanets and infrared astrophysics. confirmedas of 2026-10-10

    Revision history (2)
    1. Page created.
    2. Added L2 arrival, mass, resolution and sunshield temperatures; October 2026 fast-radio-burst host result; Webb's role in the Hubble tension with a link to the debate page.

    Created Oct 10, 2026. Last reviewed by an editor on Oct 10, 2026. Next scheduled review: Jan 10, 2027.

    Cite this page

    "James Webb Space Telescope (JWST)." ContentLora, updated Oct 10, 2026. https://contentlora.com/wiki/james-webb-space-telescope

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