What Exoplanets Has the James Webb Space Telescope Found?

TRAPPIST-1 System

One of JWST’s earliest and most anticipated targets was the TRAPPIST-1 system, a compact planetary family 40 light-years away in the constellation Aquarius. This system, already famous for its seven Earth-sized rocky planets orbiting a cool red dwarf star, has long captivated scientists and the public alike. What makes TRAPPIST-1 so special is not just the number of potentially habitable planets it hosts, but also the fact that they are all located within close orbital range, making them ideal candidates for detailed atmospheric study.

JWST’s infrared capabilities allowed it to observe secondary eclipses—when planets pass behind their star—providing precise measurements of the planets’ heat signatures and atmospheric conditions. While it found that several planets likely lack thick hydrogen atmospheres, which rules out gas giants, it also detected hints of more compact atmospheres potentially similar to Earth’s. The telescope examined TRAPPIST-1b, 1c, and 1d in particular, noting differences in thermal emission and planetary composition. One key finding: no obvious biosignatures yet, but promising signs of water retention and carbon dioxide absorption, critical for life-supporting environments.

WASP-39b

Arguably one of JWST’s most groundbreaking moments came with its analysis of WASP-39b, a hot gas giant located 700 light-years from Earth in the constellation Virgo. Known as a “hot Saturn” due to its similar mass and close orbit around its star, WASP-39b was previously observed by Hubble and Spitzer. But when JWST trained its Near-Infrared Spectrograph (NIRSpec) on the planet, it made history by detecting carbon dioxide in the atmosphere—a first for any exoplanet.

This discovery was more than just a milestone. It proved JWST’s power to detect specific molecules in alien atmospheres and map their composition with stunning detail. The carbon dioxide detection also pointed toward a complex atmospheric chemistry involving water vapor, sodium, and possibly sulfur dioxide. These findings hint at photochemical processes similar to those in Earth’s atmosphere, albeit under very different thermal conditions. WASP-39b isn’t habitable—it’s far too hot—but it serves as a Rosetta Stone for decoding other exoplanet atmospheres.

GJ 1214b

Located about 48 light-years from Earth in the constellation Ophiuchus, GJ 1214b has puzzled astronomers for years. It’s a “mini-Neptune” or “sub-Neptune” world—larger than Earth but smaller than Neptune—with a thick, cloudy atmosphere that made previous telescopic observations frustratingly inconclusive. Enter JWST, with its ability to peer through dense atmospheric veils using its Mid-Infrared Instrument (MIRI) and NIRCam.

What JWST found was a complex, hazy world with a muted infrared signature, implying high-altitude aerosols—likely photochemical smog created by ultraviolet radiation interacting with atmospheric molecules. Despite the cloudiness, JWST was able to glean temperature gradients and evidence of potential water vapor beneath the haze. Some models even suggest GJ 1214b could be a water world, with a deep ocean lying beneath a thick, steamy atmosphere. While not Earth-like in habitability, this discovery expands our catalog of planetary diversity and points to the need for understanding exoplanetary clouds and climate systems.

LHS 475b

Perhaps one of the most thrilling finds so far is LHS 475b, an Earth-sized exoplanet located just 41 light-years away in the constellation Octans. It was the first rocky planet confirmed by JWST, detected via its transit—when it passes in front of its parent star, dimming the starlight ever so slightly. What makes LHS 475b particularly exciting is not just its size and proximity, but also its similarity in mass and radius to Earth.

JWST’s spectroscopic data initially showed no obvious signs of a substantial atmosphere, but the precision was such that it could rule out thick hydrogen-dominated envelopes, like those of gas giants or mini-Neptunes. Scientists believe this leaves room for a compact atmosphere of carbon dioxide or water vapor, though more data are needed. Regardless, this discovery solidified JWST’s ability to detect rocky, terrestrial-type planets and probe them for signs of habitability—an enormous leap forward in the search for Earth 2.0.

K2-18b

K2-18b, a super-Earth or mini-Neptune located about 120 light-years away in the constellation Leo, has made headlines multiple times, but JWST brought new fire to the discussion. Previously identified as having potential water vapor by Hubble, JWST went deeper, using its Near-Infrared Imager and Slitless Spectrograph (NIRISS) to detect not just water vapor, but also methane and carbon dioxide. These are major chemical components that could suggest an atmosphere capable of supporting life, particularly in the presence of water.

Most striking was the possible detection of dimethyl sulfide (DMS)—a molecule that, on Earth, is primarily produced by marine life. While the DMS detection is still under scrutiny and far from confirmed, it raises eyebrows across the scientific community. Could K2-18b harbor alien oceans beneath its atmosphere? The planet is in its star’s habitable zone, meaning it receives just the right amount of energy to maintain liquid water, given the right conditions. This tantalizing cocktail of elements makes K2-18b one of the most promising targets for biosignature research.

HIP 65426b

While many of JWST’s discoveries come from transit spectroscopy, it also achieved a milestone in direct imaging—a notoriously difficult technique. HIP 65426b, a massive gas giant located about 385 light-years away in the Centaurus constellation, became the first exoplanet directly imaged by JWST. Using its coronagraphs to block out the parent star’s light, JWST was able to capture the planet in multiple wavelengths of infrared light.

HIP 65426b is not remotely habitable—it’s six to twelve times the mass of Jupiter and orbits its star at a distance over 90 times that of Earth from the Sun—but the ability to directly image such a distant planet is a technological triumph. The images revealed cloud patterns, thermal gradients, and even rotational hints that could provide more data on atmospheric dynamics. Most importantly, this success sets the stage for imaging smaller, potentially habitable worlds in the future.

TOI-700e

Discovered through follow-up observations from NASA’s TESS mission, TOI-700e is a rocky Earth-sized planet residing in the habitable zone of its quiet, small red dwarf star about 100 light-years away in Dorado. JWST followed up on this system, which includes at least four planets, to further characterize TOI-700e’s size, orbit, and potential atmosphere.

Initial observations suggest the planet could retain a stable, compact atmosphere, possibly similar to pre-industrial Earth. What makes TOI-700e particularly compelling is its parent star’s calm nature. Many red dwarfs exhibit frequent flares that strip atmospheres from nearby planets, but TOI-700 appears unusually stable, increasing the chance that life-supporting conditions could persist over geologic timescales. Future JWST spectroscopic missions are planned to search for trace gases like ozone and methane that might indicate biological processes.

Tantalizing Hints of Hycean Worlds and Exotic Climates

Beyond specific planetary targets, JWST is pioneering the study of an entirely new class of theoretical exoplanets known as “Hycean” worlds. These are planets with hydrogen-rich atmospheres and massive global oceans—somewhere between Earth and Neptune in size and structure. Several planets, including K2-18b and GJ 1214b, fall into this emerging category, and JWST’s data are allowing scientists to test these hypotheses.

Hycean worlds may not resemble Earth’s land-and-sea mix but could be ideal cradles for alien life. Their thick atmospheres can trap heat and protect oceans from radiation, potentially enabling life to develop under very different conditions. JWST’s data on temperature, reflectivity, and atmospheric depth are helping refine climate models and determine whether these exotic worlds could host microbial ecosystems or oceanic biospheres.

Redefining Habitability with Each New Target

JWST’s exoplanetary mission is not just about tallying new discoveries—it’s about redefining what it means for a planet to be “habitable.” Traditional models focused on temperature and liquid water, but JWST is showing that atmospheric chemistry, cloud cover, stellar activity, and even photochemical haze play equally crucial roles. By examining known and newly discovered worlds across a broad spectrum of conditions, JWST is building a library of planetary profiles that will shape future search strategies for habitable environments. Moreover, the telescope is enabling time-resolved spectroscopy—watching how atmospheres change over time during a planet’s orbit or a stellar flare. This dynamic perspective brings us closer to understanding seasonal changes, volcanic activity, or even biosignature variability on alien worlds. It’s not just snapshots of alien planets; it’s the beginnings of exoplanetary weather forecasting.

The JWST Era of Exoplanet Discovery Has Just Begun

The James Webb Space Telescope is still in the early stages of its long mission, yet it has already transformed the field of exoplanet research. With its unprecedented sensitivity to infrared light and ability to dissect the atmospheres of distant worlds, JWST is opening up a new frontier in the search for life beyond Earth. From hot Jupiters like WASP-39b to rocky Earth-sized planets like LHS 475b and tantalizing biosignature hints from K2-18b, every discovery adds a layer of understanding to the vast diversity of planetary systems in our galaxy. Each exoplanet observed by JWST becomes a case study in alien chemistry, physics, and potential biology. And with hundreds of targets already queued for study, including promising candidates from TESS and future missions, the golden age of exoplanet science is here. Whether or not we find life, JWST is giving us the next best thing: a cosmic mirror that shows how rare—or how common—our pale blue dot may truly be.