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    How exoplanets are found, and how we look for signs of life

    Astronomers have confirmed more than 6,000 planets around other stars, mostly by watching for tiny dips in starlight as planets pass in front of them.[1][2] The frontier now is reading those planets' atmospheres for gases that might signal life, which so far has produced claims but no accepted detection.[3][4]

    Editor reviewedUpdated Space exploration and astronomySpaceScience

    A fast-growing catalogue

    NASA’s count of confirmed exoplanets reached 6,000 in September 2025, three decades after the first planet around a Sun-like star was identified in 1995.[1][5] More than 8,000 further candidates were awaiting confirmation then.[1] On October 10, 2026, the NASA Exoplanet Archive listed 6,445 confirmed planets.[2]

    Four main ways to find a planet

    Planets are tiny and dim next to their stars, so most are found indirectly:

    • Transits. When a planet passes in front of its star, the star dims very slightly. Space telescopes watching many stars catch these dips.[6]
    • Wobbles (radial velocity). A planet’s gravity tugs its star back and forth. That motion squeezes and stretches the star’s light in a pattern astronomers can measure.[6]
    • Microlensing. When one star passes in front of another, its gravity acts like a lens and briefly brightens the background star. A planet around the front star adds a small extra blip.[7]
    • Direct imaging. Blocking the star’s glare to photograph the planet itself. It is hard, and fewer than 100 planets have been imaged this way.[8]

    The archive’s discovery-method breakdown on October 10, 2026 was 4,781 transit, 1,203 radial velocity, 292 microlensing and 97 imaging, with the remainder from timing and other methods.[2] Because each method sees a different slice of the planet population, a complete census needs several of them. Microlensing in particular can reveal planets that are undetectable by other methods, including analogues of the Solar System’s outer giants, which is why Roman is expected to add a statistical census of planetary systems across the galaxy.[9][10]

    Reading an atmosphere

    When a planet transits, a little starlight passes through its atmosphere on the way to us. Different gases absorb different colours, so splitting that light into a spectrum shows a barcode of the molecules in the air.[3] Webb was designed partly to do this.[11]

    Transmission spectra record wavelength-dependent absorption by the planet’s atmosphere during transit, and retrieval codes then infer composition.[3] Results can depend on data reduction choices and on which molecules are included in the model: one K2-18 b reanalysis attributed marginal preferences for DMS to limiting the molecules considered and to small differences between reductions.[4] For K2-18 b, reanalyses found that ethane or other methyl-bearing molecules fit the data as well as the claimed dimethyl sulfide.[4]

    What counts as a biosignature

    A biosignature is something that might have a biological origin but needs more evidence before anyone can conclude that life is present or absent; NASA uses this definition for its Mars finds too.[12] The difficulty is false positives: gases or minerals linked to life on Earth can sometimes form without it.[13] The best-known exoplanet case is K2-18 b, where a 2025 claim of 3-sigma evidence for dimethyl sulfide was followed by independent analyses concluding there was no statistically significant signal.[14][15] The debate is covered in the debate over evidence for life.

    Next steps

    Earth-sized planets are hard to study because their stars’ glare swamps them, so NASA is developing the Habitable Worlds Observatory to image and characterise Earth-like planets directly.[8] In the nearer term, Roman will carry out a statistical census of planetary systems across the galaxy.[10]

    Questions readers ask

    How many exoplanets are known?

    NASA's tally passed 6,000 in September 2025. On October 10, 2026 the NASA Exoplanet Archive listed 6,445 confirmed planets.[1][2]

    Which method has found the most planets?

    The transit method, which watches for dips in a star's light. It accounts for 4,781 of the 6,445 planets in the archive.[2][6]

    Have we found life on an exoplanet?

    No. A 2025 claim of possible biosignature gases on K2-18 b was challenged by several independent reanalyses that found no statistically significant evidence.[14][4][15]

    Sources

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

    1. [1]

      NASA's count of confirmed exoplanets reached 6,000 in September 2025, with more than 8,000 further candidates awaiting confirmation; the tally is kept by the NASA Exoplanet Science Institute at Caltech/IPAC. confirmedas of 2025-09-17

    2. [2]

      As of October 10, 2026 the NASA Exoplanet Archive listed 6,445 confirmed planets, of which 4,781 were found by the transit method, 1,203 by radial velocity, 292 by microlensing and 97 by direct imaging. confirmedas of 2026-10-10

    3. [3]

      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

    4. [4]

      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

    5. [5]

      The first exoplanet orbiting a Sun-like star was identified in 1995. confirmedas of 2025-09-17

    6. [6]

      The transit method finds planets through the small dip in a star's light when a planet crosses in front of it; the radial velocity method detects the star's wobble as shifts in the wavelengths of its light. confirmedas of 2026-10-10

    7. [7]

      In gravitational microlensing, the gravity of a foreground star magnifies the light of a background star passing behind it, and a planet around the foreground star adds its own signal. confirmedas of 2026-10-10

    8. [8]

      Fewer than 100 exoplanets have been directly photographed, and studying the atmospheres of Earth-sized planets is hard because of their stars' glare; NASA is developing the Habitable Worlds Observatory to characterize Earth-like planets. confirmedas of 2025-09-17

    9. [9]

      Roman will use gravitational microlensing, which detects planets through the way their gravity bends light from background stars, to find planets that other methods cannot, including analogues of the Solar System's outer giant planets. reportedas of 2026-08-28

    10. [10]

      NASA says Roman will complete a statistical census of planetary systems in our galaxy and could measure light from a billion galaxies over its lifetime. 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 September 2025 NASA said a Perseverance rock core called Sapphire Canyon, drilled in July 2024 from the Cheyava Falls rock in Jezero Crater, contains a potential biosignature, reported in a peer-reviewed Nature paper. confirmedas of 2025-09-10

    13. [13]

      NASA scientists said the mineral "leopard spots" in the Cheyava Falls rock can also form without life, and that although non-biological explanations are less likely they cannot be ruled out. confirmedas of 2025-09-10

    14. [14]

      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

    15. [15]

      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

    Revision history (1)
    1. Page created.

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

    Cite this page

    "How exoplanets are found, and how we look for signs of life." ContentLora, updated Oct 10, 2026. https://contentlora.com/explain/how-exoplanets-are-found

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