00 · IN THREE MINUTES

The answer in three steps

  1. 1A is a feature that may have a biological origin, not a synonym for life detected.
  2. 2The same signal can be produced by geology, photochemistry, contamination or instruments, so environmental context matters.
  3. 3Confidence rises when independent observations agree and plausible non-biological explanations fail.

01 · A CLUE IS NOT A VERDICT

A clue is not a verdict

A gas, pigment, isotope pattern or complex molecule becomes interesting because life can produce it. But “can” is not “must.” Science begins by asking how specific the clue is and what else could generate it.

02 · READ THE ENVIRONMENT FIRST

Read the environment first

Oxygen beside methane may be more informative than either gas alone, yet stellar ultraviolet light, atmospheric escape and rock chemistry change the interpretation. A biosignature belongs to a planetary system, not an isolated spectrum line.

FIG. 02A ladder of increasing confidence
Moving upward requires more than a stronger signal: each rung closes a different failure mode.

03 · CONTROL THE INSTRUMENT AND THE SAMPLE

Control the instrument and the sample

A signal must survive checks for detector artifacts, data-processing choices and contamination from Earth. For returned samples, the chain of custody and blank controls are part of the biological claim.

04 · TRY TO KILL THE HYPOTHESIS

Try to kill the hypothesis

Researchers model abiotic pathways and ask whether they can explain the amount, location and persistence of the signal. Strong evidence is not the absence of imagination; it is the failure of well-specified alternatives.

FIG. 03 · INTERACTIVEA ladder of increasing confidence

Moving upward requires more than a stronger signal: each rung closes a different failure mode.

1

Detect

Show that the signal is real and repeatable.

instrument check
Moving upward requires more than a stronger signal: each rung closes a different failure mode.

05 · DEMAND CONVERGENCE

Demand convergence

Multiple instruments, repeated observations and different kinds of evidence should point in the same direction. Chemistry, morphology and environmental disequilibrium are more persuasive together than as isolated curiosities.

06 · USE CALIBRATED LANGUAGE

Use calibrated language

Possible, plausible, probable and confirmed should not be interchangeable. NASA’s life-detection frameworks exist to keep a striking observation from becoming a premature announcement.

07 · SOURCES AND EVIDENCE

Sources and evidence

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

  1. 01
    Exoplanet Biosignatures: A Framework for Their Assessment

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

    PEER-REVIEWED REVIEW ↗
  2. 02
    Ladder of Life Detection

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

    OFFICIAL REFERENCE ↗
  3. 03
    NASA Astrobiology Strategy

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

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