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EXOPLANET BIOSIGNATURES

The problemsEarth & SpaceExoplanet Biosignatures

Updated · July 2026

How close are we to detecting life on an exoplanet?Could we recognize life on a world around another star?

Could we recognize life on a world around another star?How close are we to detecting life on an exoplanet?

Atmospheric spectroscopy is now routine for some large exoplanets, but no world beyond Earth has yielded a confirmed biosignature; the observatory intended to survey nearby potentially habitable worlds remains in development.We know more than 6,000 planets beyond our Solar System, but zero confirmed living ones. The next leap needs a telescope that can separate an Earth-like planet from a star ten billion times brighter.

Current stageEngineeringEngineering a system that works outside the labBuilding a system that works outside the lab
Read the evidence Where we stand
The path so far

Recorded milestones

  1. First exoplanets confirmed

  2. Six thousand planets, no confirmed life

Open tests · conceptual branches

TODAY
  1. OPEN TEST03 ↗
    Find a bundle of life cluesDetect biosignatures in planetary contextA single gas is not enough: geology, light-driven chemistry or the host star can imitate it.Measure a combination of potentially biological gases together with the planet's climate, host-star environment and leading abiotic alternatives.
  2. OPEN TEST04 ↗
    See it again and rule out impostorsSurvive independent confirmationNASA says there is still no evidence of life beyond Earth.Independent observations and retrieval methods reproduce the signal while plausible non-biological explanations fail.
TODAY
OPEN TEST03 ↗
Find a bundle of life cluesDetect biosignatures in planetary contextA single gas is not enough: geology, light-driven chemistry or the host star can imitate it.Measure a combination of potentially biological gases together with the planet's climate, host-star environment and leading abiotic alternatives.
OPEN TEST04 ↗
See it again and rule out impostorsSurvive independent confirmationNASA says there is still no evidence of life beyond Earth.Independent observations and retrieval methods reproduce the signal while plausible non-biological explanations fail.
Milestones are in recorded order. Open tests are separate questions, not a forecast.Milestones are in date order. Open tests are separate tests, not a promise.
Exoplanet BiosignaturesWhere we stand

The path shows Six thousand planets, no confirmed life. Open thresholds are separate tests in a conceptual map, not a forecast. No single percentage represents progress.

01 · Where we standWhere we stand

Where we standWhere we stand

The current stage, the evidence recorded, and the single threshold that gates the next stage.The stage reached, the evidence recorded, and the one test still blocking the next step.

What the evidence has shownWhat the evidence has shown

We know more than 6,000 planets beyond our Solar System, but zero confirmed living ones. The next leap needs a telescope that can separate an Earth-like planet from a star ten billion times brighter.Atmospheric spectroscopy is now routine for some large exoplanets, but no world beyond Earth has yielded a confirmed biosignature; the observatory intended to survey nearby potentially habitable worlds remains in development.

2 of 4 tests recorded2 of 4 thresholds achieved open
✓Prove other worlds are commonEstablish the exoplanet populationAchieved
✓Read gases in an alien skyMeasure exoplanet atmospheric chemistryAchieved
Find a bundle of life cluesDetect biosignatures in planetary contextOpen test
See it again and rule out impostorsSurvive independent confirmationOpen test

The next testBlocking threshold

Find a bundle of life cluesDetect biosignatures in planetary context

Obtain a repeatable spectrum of an Earth-sized habitable-zone world that constrains several gases and its environmental context.Obtain a repeatable spectrum of an Earth-sized habitable-zone world that constrains several gases and its environmental context.

02 · Thresholds & evidenceThresholds & evidence

What would count as proof?What would count as proof?

A clear test, the evidence behind it, and the limits of the claim.A clear test, the evidence behind it, and what it still leaves open.

✓Achieved · Sep 2025

Prove other worlds are commonEstablish the exoplanet population

More than 6,000 exoplanets are confirmed. A large census supplies targets; it is not evidence of life.Confirm planets around other stars and measure enough systems to establish their abundance and diversity.

Recorded result NASA's confirmed-exoplanet tally passed 6,000.

Next test PLATO begins measuring terrestrial planets and their bright Sun-like host stars after launch.

SOURCE RECORD

NASA — 6,000 confirmed exoplanets (17 Sep 2025) ↗

Still to demonstrateWhat this does not establishA separate system can still have different conditions and results.The named measurement has no wider implication until the supporting system test is also shown.

View every evidence record

Achieved

Prove other worlds are commonEstablish the exoplanet population

More than 6,000 exoplanets are confirmed. A large census supplies targets; it is not evidence of life.Confirm planets around other stars and measure enough systems to establish their abundance and diversity.

Recorded result: Sep 2025 · NASA's confirmed-exoplanet tally passed 6,000.

Next test: PLATO begins measuring terrestrial planets and their bright Sun-like host stars after launch.

NASA — 6,000 confirmed exoplanets (17 Sep 2025) ↗

Achieved

Read gases in an alien skyMeasure exoplanet atmospheric chemistry

Hubble and Webb have measured molecules, mainly on large or hot planets whose atmospheres are easier to see.Recover repeatable molecular constraints from an exoplanet spectrum rather than infer composition from bulk size and mass alone.

Recorded result: Nov 2001 · Hubble detected sodium in HD 209458 b's atmosphere.

Next test: Repeat robust atmospheric constraints on a temperate, Earth-sized habitable-zone planet.

NASA — Hubble first direct exoplanet atmosphere measurement ↗

Open test

Find a bundle of life cluesDetect biosignatures in planetary context

A single gas is not enough: geology, light-driven chemistry or the host star can imitate it.Measure a combination of potentially biological gases together with the planet's climate, host-star environment and leading abiotic alternatives.

Next test: Obtain a repeatable spectrum of an Earth-sized habitable-zone world that constrains several gases and its environmental context.

Open test

See it again and rule out impostorsSurvive independent confirmation

NASA says there is still no evidence of life beyond Earth.Independent observations and retrieval methods reproduce the signal while plausible non-biological explanations fail.

Next test: A second instrument reproduces a candidate spectrum and independent teams reach compatible conclusions after explicit false-positive tests.

03 · The recordThe record

The record behind the verdictThe record behind the verdict

Major milestones and smaller context events share one source-linked record. Scheduled targets are marked separately from recorded events.Milestones, smaller events and setbacks share one sourced record. Scheduled targets are marked separately from recorded events.

Event key
TheoryExperimentFundingSetbackPolicyDeployment Future / scheduled
1992-20002 events2 shown

Other worlds become real

This record spans “First exoplanets confirmed” to “Planet found around a Sun-like star”.

1992
First exoplanets confirmedExperiment
Timing variations revealed two planets around pulsar PSR B1257+12, the first confirmed worlds beyond the Solar System.
Aleksander Wolszczan and Dale Frail
1995
Planet found around a Sun-like starExperiment
51 Pegasi b became the first reliably identified planet orbiting an ordinary main-sequence star.
Michel Mayor and Didier Queloz
2001-20081 event1 shown

Atmospheres enter the spectrum

Recorded event: “First exoplanet atmosphere measured”.

2001
First exoplanet atmosphere measuredExperiment
Hubble detected sodium in HD 209458 b, the first direct chemical measurement of an exoplanet atmosphere.
Hubble Space Telescope team
2009-20204 events2 shown

The planet census scales

This record spans “Kepler begins a planet census” to “TESS starts surveying nearby stars”.

2009
Kepler begins a planet censusDeployment
Kepler launched to measure the prevalence and diversity of planets through transits, ultimately confirming more than 2,600 worlds.
NASA
2013
Kepler loses precision pointing
A second reaction wheel failed after four years, ending continuous monitoring of the original field before the spacecraft was repurposed as K2.
NASA Kepler mission
2017
Seven Earth-sized worlds revealedExperiment
The TRAPPIST-1 system was shown to contain seven Earth-sized planets, three in the star's conventional habitable zone.
TRAPPIST and Spitzer teams
2018
TESS starts surveying nearby stars
TESS launched to find transiting planets around bright nearby stars that are better suited to follow-up measurements.
NASA and MIT
2021-20264 events2 shown

Rocky atmospheres face scrutiny

This record spans “Webb launches infrared observatory” to “Confirmed planets pass six thousand”.

2021
Webb launches infrared observatoryDeployment
JWST launched with infrared instruments capable of characterizing selected exoplanet atmospheres.
NASA, ESA and CSA
2023
TRAPPIST-1 b appears airless
Webb measured a dayside temperature near 500 K, consistent with bare rock and no significant atmosphere on this innermost rocky planet.
JWST MIRI team
2023
K2-18 b gases measured
Webb detected methane and carbon dioxide on a 2.6-Earth-radius sub-Neptune. A possible dimethyl-sulfide feature was less robust and required validation.
JWST NIRISS and NIRSpec team
2025
Confirmed planets pass six thousandExperimentWe are here
NASA's archive reached 6,000 confirmed exoplanets, with more than 8,000 candidates awaiting confirmation; none constitutes confirmed evidence of life.
NASA Exoplanet Archive
2027-20493 events0 shown

Building a habitable-world survey

Scheduled targets in this record run from “PLATO planned to launch” to “HWO targets direct imaging”.

2027
PLATO planned to launchDeploymentTarget
ESA plans to launch its completed 26-camera spacecraft to find and characterize terrestrial planets around bright Sun-like stars; it remains in final testing.
European Space Agency
2031
Ariel planned to begin its journeyDeploymentTarget
ESA lists 2031 for Ariel's launch. Its objective is a chemical census of about 1,000 mainly warm and hot exoplanets, not 1,000 Earth analogues.
European Space Agency
2040
HWO targets direct imagingDeploymentTarget
NASA's conditional planning target places an HWO-class launch in the first half of the 2040s if technology maturation succeeds. The mission's design objective is to image 25 potentially habitable worlds, not detect 25 biospheres.
NASA
— end of record · 14 events shown —
04 · The dataThe data

The data behind the verdictThe data behind the verdict

Read each measure with its units, conditions, uncertainty and source; targets remain distinct from observations.Read each chart with its conditions, limits and source. Future targets remain distinct from recorded results.

Open figure in archive: Planet discovery has scaled from two confirmed worlds to more than 6,000. This is target supply and population context, not progress from zero toward a life detection.Open figure in archive: These missions answer different questions. Ariel's broad atmospheric census and HWO's smaller potentially habitable-world objective are target samples, not expected biosphere detections.Open figure in archive: In visible reflected light, an Earth-sized planet around a Sun-like star is about ten billion times dimmer than its host, defining the starlight-suppression challenge.
Confirmed exoplanet biospheresConfirmed exoplanet biospheres
Scale

NASA reports no evidence of life beyond Earth · 0 biospheres · 2026 · verification unspecified

Confirmed exoplanet biospheres over time, with measured values, projected values, and a goal at 1 biospheres.-1-0.500.511.52Confirmed exoplanet biospheres · biospheresYear2026GOAL 1 · First independently supported det…NASA reports no evidence of…~1 biospheres to goal
NOTE - Zero is the honest current count. Interesting molecules and habitable-zone locations do not qualify without planetary context, false-positive tests and independent confirmation. HWO's separate 25-world survey objective is not a projection of this metric.
View data table
All metric observations
DateValueStatusCondition / labelVerificationCICensoringSource
20260 biospheresobservedNASA reports no evidence of life beyond Earthunspecified—noneNASA - Are We Alone?
AS OF July 2026
View every data figure
Confirmed exoplanet biospheresConfirmed exoplanet biospheres
Scale

NASA reports no evidence of life beyond Earth · 0 biospheres · 2026 · verification unspecified

Confirmed exoplanet biospheres over time, with measured values, projected values, and a goal at 1 biospheres.-1-0.500.511.52Confirmed exoplanet biospheres · biospheresYear2026GOAL 1 · First independently supported det…NASA reports no evidence of…~1 biospheres to goal
NOTE - Zero is the honest current count. Interesting molecules and habitable-zone locations do not qualify without planetary context, false-positive tests and independent confirmation. HWO's separate 25-world survey objective is not a projection of this metric.
View data table
All metric observations
DateValueStatusCondition / labelVerificationCICensoringSource
20260 biospheresobservedNASA reports no evidence of life beyond Earthunspecified—noneNASA - Are We Alone?
AS OF July 2026
Planet discovery has scaled from two confirmed worlds to more than 6,000. This is target supply and population context, not progress from zero toward a life detection.Planet discovery has scaled from two confirmed worlds to more than 6,000. This is target supply and population context, not progress from zero toward a life detection.

log scale · planets by year

First confirmed system · 2 planets · Jan 1992 · verification unspecified

Planet discovery has scaled from two confirmed worlds to more than 6,000. This is target supply and population context, not progress from zero toward a life detection.First confirmed system: 2 planets · Jan 1992NASA archive milestone: 5,000 planets · Jan 20226,000 planets · Jan 2025NASA archive milestone: 6,000 planets · Jan 2025Year
Log-scale line joins each new longest record; all observations remain individual dots.

First record

First confirmed system

2 planets · Jan 1992

observed · Verification unspecified

Latest record

NASA archive milestone

6,000 planets · Jan 2025

observed · Verification unspecified

View data table
All plotted observations
SeriesDateValueStatusCondition / labelVerificationCICensoringSource
Confirmed exoplanet census milestones19922 planetsobservedFirst confirmed systemunspecified—noneTimeline · First exoplanets confirmed
Confirmed exoplanet census milestones20225000 planetsobservedNASA archive milestoneunspecified—noneSeries · Confirmed exoplanet census milestones
Confirmed exoplanet census milestones20256000 planetsobservedNASA archive milestoneunspecified—noneNASA - 6,000 confirmed exoplanets
AS OF July 2026
These missions answer different questions. Ariel's broad atmospheric census and HWO's smaller potentially habitable-world objective are target samples, not expected biosphere detections.These missions answer different questions. Ariel's broad atmospheric census and HWO's smaller potentially habitable-world objective are target samples, not expected biosphere detections.

Independent records

Future mission sample objectives log scale · worlds

log scale · worlds
Ariel chemical census - mainly warm and hot planets20311,000 worlds · pathway
HWO potentially habitable direct-imaging objective204025 worlds · target
observed self-reported target / pathway right-censored lower bound
View data table
All plotted observations
SeriesDateValueStatusCondition / labelVerificationCICensoringSource
Future mission sample objectives20311000 worldspathwayAriel chemical census - mainly warm and hot planetsunspecified—noneESA - Ariel mission
Future mission sample objectives204025 worldstargetHWO potentially habitable direct-imaging objectiveunspecified—noneNASA - Habitable Worlds Observatory
AS OF July 2026
In visible reflected light, an Earth-sized planet around a Sun-like star is about ten billion times dimmer than its host, defining the starlight-suppression challenge.In visible reflected light, an Earth-sized planet around a Sun-like star is about ten billion times dimmer than its host, defining the starlight-suppression challenge.

log scale · star-to-planet brightness ratio by year

Sun-like star versus reflected light from an Earth-sized planet · 1e+10 star-to-planet brightness ratio · Jan 2026 · verification unspecified

In visible reflected light, an Earth-sized planet around a Sun-like star is about ten billion times dimmer than its host, defining the starlight-suppression challenge.1e+10 star-to-planet brightness ratio · Jan 2026Sun-like star versus reflected light from an Earth-sized planet: 1e+10 star-to-planet brightness ratio · Jan 2026Year
Log-scale line joins each new longest record; all observations remain individual dots.

Latest record

Sun-like star versus reflected light from an Earth-sized planet

1e+10 star-to-planet brightness ratio · Jan 2026

observed · Verification unspecified

View data table
All plotted observations
SeriesDateValueStatusCondition / labelVerificationCICensoringSource
Earth-twin visible-light contrast202610000000000 star-to-planet brightness ratioobservedSun-like star versus reflected light from an Earth-sized planetunspecified—noneNASA - direct-imaging contrast challenge
AS OF July 2026

Methods & conditions

Under the measurement.

The boundary of a measurement changes what it means.

Technical note 1 of 3

K2-18 b is not an Earth twin

Method and conditions

NASA reports a radius 2.6 times Earth's and a mass 8.6 times Earth's. Methane and carbon dioxide are robust atmospheric constraints; the 2023 dimethyl-sulfide inference was less robust, and a habitable surface is not established.

Source notes
NASA - Webb spectrum of K2-18 b

Technical notes and sources

Each note keeps its authored method, conditions and citations available for review.

K2-18 b is not an Earth twin

NASA reports a radius 2.6 times Earth's and a mass 8.6 times Earth's. Methane and carbon dioxide are robust atmospheric constraints; the 2023 dimethyl-sulfide inference was less robust, and a habitable surface is not established.

NASA - Webb spectrum of K2-18 b
A biosignature is a contextual inference

Oxygen, methane or another molecule is not a verdict on its own. A credible interpretation must account for the planet's atmosphere, climate, stellar irradiation and non-biological production pathways.

NASA - the search for life NASA - living Earth as context
Mission sample is not detection yield

HWO's stated objective is to identify and directly image 25 potentially habitable worlds. It does not assert that 25 will be inhabited-or that any biosignature will be confirmed.

NASA - Habitable Worlds Observatory
05 · What it unlocksWhat it unlocks

If the remaining tests pass.If the remaining tests pass.

Downstream capabilities remain conditional on results that are not yet in.These are possible next capabilities, conditional on results that are not yet in.

TODAY
  1. PASSED · Nov 200102 ↗
    Read gases in an alien skyMeasure exoplanet atmospheric chemistryHubble and Webb have measured molecules, mainly on large or hot planets whose atmospheres are easier to see.Recover repeatable molecular constraints from an exoplanet spectrum rather than infer composition from bulk size and mass alone.
  2. PASSED · Sep 202501 ↗
    Prove other worlds are commonEstablish the exoplanet populationMore than 6,000 exoplanets are confirmed. A large census supplies targets; it is not evidence of life.Confirm planets around other stars and measure enough systems to establish their abundance and diversity.
  3. OPEN TEST03 ↗
    Find a bundle of life cluesDetect biosignatures in planetary contextA single gas is not enough: geology, light-driven chemistry or the host star can imitate it.Measure a combination of potentially biological gases together with the planet's climate, host-star environment and leading abiotic alternatives.
  4. OPEN TEST04 ↗
    See it again and rule out impostorsSurvive independent confirmationNASA says there is still no evidence of life beyond Earth.Independent observations and retrieval methods reproduce the signal while plausible non-biological explanations fail.
PASSED · Nov 200102 ↗
Read gases in an alien skyMeasure exoplanet atmospheric chemistryHubble and Webb have measured molecules, mainly on large or hot planets whose atmospheres are easier to see.Recover repeatable molecular constraints from an exoplanet spectrum rather than infer composition from bulk size and mass alone.
PASSED · Sep 202501 ↗
Prove other worlds are commonEstablish the exoplanet populationMore than 6,000 exoplanets are confirmed. A large census supplies targets; it is not evidence of life.Confirm planets around other stars and measure enough systems to establish their abundance and diversity.
TODAY
OPEN TEST03 ↗
Find a bundle of life cluesDetect biosignatures in planetary contextA single gas is not enough: geology, light-driven chemistry or the host star can imitate it.Measure a combination of potentially biological gases together with the planet's climate, host-star environment and leading abiotic alternatives.
OPEN TEST04 ↗
See it again and rule out impostorsSurvive independent confirmationNASA says there is still no evidence of life beyond Earth.Independent observations and retrieval methods reproduce the signal while plausible non-biological explanations fail.

Possible, if the open tests pass.

  1. A second known origin of life

    This is a possible benefit only if a second known origin of life works safely, reliably and at useful scale.Potential benefit only if the stated use (A second known origin of life) is demonstrated with evidence for safety, reliability, affordability and scale.

  2. Comparative planetary biology

    This is a possible benefit only if comparative planetary biology works safely, reliably and at useful scale.Potential benefit only if the stated use (Comparative planetary biology) is demonstrated with evidence for safety, reliability, affordability and scale.

  3. Sharper searches for living worlds

    This is a possible benefit only if sharper searches for living worlds works safely, reliably and at useful scale.Potential benefit only if the stated use (Sharper searches for living worlds) is demonstrated with evidence for safety, reliability, affordability and scale.

These are possible outcomes, if the open tests pass. They are conditional, not promises.
06 · SourcesSources

Follow the evidence.Follow the evidence.

18 sources — every figure on this page traces to one.18 sources — every figure on this page traces to one.

Source · what this page citesScope and limits
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  8. 08

    NASA — 6,000 confirmed exoplanets (17 Sep 2025)

    Read source ↗nasa.gov
    Used on this page
    All 1 use across 1 destination

    Scope: Not recorded. Limit: Not recorded.

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    Timeline · Seven Earth-sized worlds revealed

    Read source ↗science.nasa.gov
    Used on this page
    All 2 uses across 2 destinations

    Scope: Not recorded. Limit: Not recorded.

  13. 13

    Timeline · TESS starts surveying nearby stars

    Read source ↗science.nasa.gov
    Used on this page
    All 2 uses across 2 destinations

    Scope: Not recorded. Limit: Not recorded.

  14. 14

    Timeline · Webb launches infrared observatory

    Read source ↗science.nasa.gov
    Used on this page
    All 2 uses across 2 destinations

    Scope: Not recorded. Limit: Not recorded.

  15. 15

    Timeline · TRAPPIST-1 b appears airless

    Read source ↗nasa.gov
    Used on this page
    All 2 uses across 2 destinations

    Scope: Not recorded. Limit: Not recorded.

  16. 16

    Timeline · HWO targets direct imaging

    Read source ↗assets.science.nasa.gov
    Used on this page
    All 2 uses across 2 destinations

    Scope: Not recorded. Limit: Not recorded.

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    Scope: Not recorded. Limit: Not recorded.

  18. 18

    Engineer note · A biosignature is a contextual inference

    Read source ↗science.nasa.gov

    Scope: Not recorded. Limit: Not recorded.

Sources describe evidence. Inclusion is not endorsement.