The James Webb Space Telescope is the largest and most powerful space observatory ever launched.
It watches the universe in infrared light from a cold vantage point far from Earth.
Must Know
The Telescope and Its Unique Features
What Webb is and when it launched
- LaunchThe James Webb Space Telescope is the largest space telescope ever launched.
- DateIt lifted off on 25 December 2021 from Kourou in French Guiana.
- RocketAn Ariane 5 rocket provided by ESA carried it into space.
- PartnersNASA leads the mission with the European and Canadian space agencies.
- OrbitWebb arrived at its working orbit around L2 in January 2022.
The giant segmented mirror
- MirrorWebb’s primary mirror is 6.5 metres across, made of 18 hexagonal segments.
- MaterialEach segment is built of beryllium and coated with a thin layer of gold.
- GoldGold reflects infrared light far better than ordinary coatings do.
- GatheringThe mirror collects about six times more light than Hubble’s 2.4-metre mirror.
- FoldingThe segments fold for launch, then unfold and align in space.
The five-layer sunshield
- ShieldA sunshield the size of a tennis court shades the telescope.
- LayersIt has five ultra-thin layers of coated kapton film.
- BlockingThe shield blocks heat from the Sun, Earth and Moon together.
- ColdMost instruments work near minus 233 degrees Celsius in its shadow.
- ResultSuch deep cold lets faint infrared signals stand out clearly.
Where Webb works: the L2 point
- PositionWebb orbits the Sun-Earth L2 Lagrange point, 1.5 million km from Earth.
- GeometryL2 lies on the side of Earth facing away from the Sun.
- AdvantageFrom there the telescope keeps all three light sources behind one shield.
- ContrastHubble orbits Earth; Webb instead orbits far beyond the Moon.
The four science instruments
- NIRCamNIRCam takes deep images in near-infrared light.
- NIRSpecNIRSpec captures spectra of many objects at once.
- MIRIMIRI sees mid-infrared light and is cooled the most.
- NIRISSNIRISS and the Fine Guidance Sensor aim and stabilise the telescope.
- PartnersEuropean and Canadian partners built key parts of these instruments.
Good to Know
Why Infrared, and How Webb Beats Its Predecessors
Why Webb works in infrared light
- Cold ObjectsInfrared reveals objects too cold to shine in visible light.
- RedshiftThe earliest light is stretched into infrared by cosmic expansion.
- DustDust hides newborn stars from visible-light telescopes.
- PenetrationInfrared passes through dust and exposes the stars inside.
Webb versus Hubble and Spitzer
- HubbleHubble observes mainly visible and ultraviolet light from low Earth orbit.
- SpitzerSpitzer was a small infrared telescope with a mirror under one metre.
- ScaleWebb’s mirror is far larger and its instruments far colder.
- ReachWebb sees the first galaxies that Hubble cannot reach.
- ServicingUnlike Hubble, Webb cannot be serviced by astronauts.
- AutonomyIt unfolded itself in orbit and now runs autonomously.
The key goals of the mission
- First LightGoal one: see the first stars and galaxies after the Big Bang.
- GalaxiesGoal two: trace how galaxies assemble and evolve over time.
- Star BirthGoal three: study how stars and planets are born in dust.
- ExoplanetsGoal four: read exoplanet atmospheres for water and other gases.
- CosmologyDeep surveys may also probe dark matter and dark energy.
- Solar SystemThe telescope also studies objects in our own solar system.
How a huge telescope fits in a rocket
- FoldingThe mirror and sunshield fold up inside the rocket’s nose cone.
- DeploymentThe structure finished unfolding about two weeks after launch.
- AlignmentTiny motors behind each segment align them into one mirror.
- FocusControllers kept adjusting until the mirror focused perfectly.
Test Yourself
Great to Know
First Results, Records and the Long Road to Launch
First full-colour images (July 2022)
- ReleaseWebb released its first full-colour images on 12 July 2022.
- Deep FieldThe first deep field revealed galaxy cluster SMACS 0723.
- WealthThousands of galaxies crowd that single patch of sky.
- TargetsThe set also included the Carina Nebula and Stephan’s Quintet.
- SpectrumWebb even delivered a spectrum of exoplanet WASP-96b.
Record-breaking galaxies
- FrontierWebb keeps finding galaxies from the universe’s first billion years.
- RecordIn 2024 it confirmed JADES-GS-z14-0, the most distant galaxy then known.
- AgeThat galaxy existed just 290 million years after the Big Bang.
- DistanceIts light has travelled for more than 13.5 billion years.
- ModelsSuch early galaxies challenge existing models of formation.
Exoplanet atmosphere science
- MethodWebb reads the atmospheres of planets around other stars.
- K2-18bIt found water, methane and carbon dioxide on K2-18b.
- WASP-39bWASP-39b yielded a rich inventory of atmospheric gases.
- HabitabilityThis work is a step toward detecting habitable worlds.
The long road to launch
- OriginsThe mission began in the 1990s as the Next Generation Space Telescope.
- DelaysCost and redesign problems pushed launch from 2007 to 2021.
- CostThe final cost reached about 10 billion US dollars.
- NameThe telescope honours James E. Webb, NASA’s second administrator.
Current Affairs
📺 Current Affairs
Webb has remained in the news through 2024–25 with striking exoplanet findings.
An exoplanet whose composition defies explanation (2025)
- ReleaseIn late 2025, NASA reported a Webb finding on an exotic exoplanet.
- PlanetThe object, PSR J2322-2650b, is a Jupiter-mass planet orbiting a pulsar.
- AtmosphereIts atmosphere is dominated by helium and carbon, unlike any known before.
- CloudsCarbon clouds may condense into soot and even diamonds deep below.
- PuzzleThe result challenges current ideas about how such planets form.
- SourceSTScI News Release 2025-134 — NASA’s Webb Observes Exoplanet Whose Composition Defies Explanation
K2-18b: methane, carbon dioxide and a possible biosignature (2023)
- DiscoveryIn September 2023, Webb found methane and carbon dioxide on K2-18b.
- WorldK2-18b is a Hycean planet about 8.6 times Earth’s mass.
- SignalWebb also saw a tentative signal of dimethyl sulfide, a gas life makes on Earth.
- DebateThe signal remains unconfirmed, and follow-up studies continue through 2025.
- SourceNASA Science — Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18 b
55 Cancri e: an atmosphere on a rocky super-Earth? (2024)
- FindingIn May 2024, NASA reported Webb hints of an atmosphere on 55 Cancri e.
- World55 Cancri e is a rocky super-Earth that orbits very close to its star.
- GasesThe gases may be outgassing from a magma ocean on the planet’s surface.
- SignificanceIt would be the best evidence yet of an atmosphere on a rocky exoplanet.
- SourceNASA Science — NASA’s Webb Hints at Possible Atmosphere Surrounding Rocky Exoplanet
PYQ
Previous Year Questions
2022 Mains — GS Paper III
- Mains 2022UPSC CSM 2022 GS Paper III, Q15 — View this question
- AskThe question seeks unique features and the mission’s key goals.
- PlanCompare Webb with Hubble and Spitzer, then list the four goals.
- TipName L2, infrared, the 6.5-metre mirror and the sunshield for full marks.
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