00 · IN THREE MINUTES

The answer in three steps

  1. 1A transiting planet blocks its star, and its atmosphere filters a thin ring of starlight.
  2. 2Molecules absorb characteristic combinations of wavelengths.
  3. 3Researchers fit physical models while testing clouds, stellar activity and instrumental effects that can mimic or hide features.

01 · SUBTRACT THE STAR FROM THE TRANSIT

Subtract the star from the transit

A telescope records the stellar spectrum outside transit and the combined planet-star signal during transit. The wavelength-dependent change is extremely small, but it contains the atmosphere's .

02 · MOLECULES LEAVE PATTERNS, NOT LABELS

Molecules leave patterns, not labels

Water, carbon dioxide, methane and other molecules absorb sets of wavelengths determined by quantum transitions. Identification depends on matching several features at the right strengths, not finding one isolated bump.

03 · CLOUDS FLATTEN THE CODE

Clouds flatten the code

Clouds and hazes can block the deeper atmosphere and mute spectral structure. Temperature, pressure, gravity and composition also trade off against one another when a retrieval model fits the data.

FIG. 02 · INTERACTIVEHow the evidence fits together

A conceptual model: the geometry shows relationships, not measured scale.

1

Subtract the star from the transit

A telescope records the stellar spectrum outside transit and the combined planet-star signal during transit. The wavelength-dependent change is extremely small, but it contains the atmosphere's transmission spectrum.

out minus in
A conceptual model: the geometry shows relationships, not measured scale.

04 · THE STAR IS PART OF THE MEASUREMENT

The star is part of the measurement

Starspots and bright regions make the illuminating spectrum uneven. If that stellar contamination is not modeled, a feature attributed to a planet can be biased or even created.

05 · DETECTION IS NOT HABITABILITY

Detection is not habitability

Finding a molecule establishes a chemical constraint under a model. It does not by itself establish surface conditions, biological origin or life; those require wider context and independent tests.

06 · SOURCES AND EVIDENCE

Sources and evidence

The explanation follows the evidence chain below. Links open the original source.

  1. 01
    How We Find and Characterize Exoplanets

    Supports a specific claim or evidence boundary used in this article.

    INSTITUTIONAL EXPLAINER ↗
  2. 02
    How Will Webb Study Exoplanets?

    Supports a specific claim or evidence boundary used in this article.

    OFFICIAL DATA / TECHNICAL REPORT ↗
  3. 03
    Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects

    Supports a specific claim or evidence boundary used in this article.

    PEER-REVIEWED REVIEW ↗
CHANGE LOG28 Aug 2026 · First five-language edition; claims, evidence boundaries and visual model checked.