Confidence of Life Detection Scale (CoLD) or the Ladder of Life Detection is a numerical scale developed by NASA astrobiologists to assess possible

biosignature A biosignature (sometimes called chemical fossil or molecular fossil) is any substance – such as an element, isotope, molecule, or phenomenon – that provides scientific evidence of past or present life on a planet. Measurable ...

s of

extraterrestrial life Extraterrestrial life, or alien life (colloquially, aliens), is life that originates from another world rather than on Earth. No extraterrestrial life has yet been scientifically conclusively detected. Such life might range from simple forms ...

. It was suggested in 2018. The scale is designed similar to NASA’s technological readiness scale. It is a seven-step scale: # Detect possible signal # Rule out contamination # Make sure biology is possible # Rule out non-biology # Find additional independent signal # Rule out other hypothesis # Independent confirmation

History

NASA's "working definition of life" is "self-sustaining chemical system capable of Darwinian evolution". As of 2025, the only NASA mission designed to look for life was the

Viking program The ''Viking'' program consisted of a pair of identical American space probes, ''Viking 1'' and ''Viking 2'' both launched in 1975, and landed on Mars in 1976. The mission effort began in 1968 and was managed by the NASA Langley Research Cent ...

to Mars, launched in 1976. Per Neveu et al.: The Ladder is designed to "define the burden of proof that must be met to convince a majority of the scientific community of such a discovery." Neveu et al. lists eight criteria:

Examples

The

Cheyava Falls Cheyava Falls is a rock discovered on Mars by NASA's ''Perseverance (rover), Perseverance'' rover during its exploration of the Jezero Crater. This rock, named after a Grand Canyon waterfall, has drawn significant attention due to its potential as ...

rock, found by the ''

Perseverance Perseverance most commonly refers to: * ''Perseverance'' (rover), a planetary rover landed on Mars by NASA * Psychological resilience Perseverance may also refer to: Geography * Perseverance, Queensland, a locality in Australia * Perseverance I ...

'' rover on Mars in 2024, is an example of a step one on the CoLD scale, a detect of a possible signal. If

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

will be found on Mars, it would be assessed as level four of the scale.

Criticism

CoLD scale was criticized as a useless tool that doesn't solve existing issues in scientific reporting: "CoLD scale is an inapt and easily abused tool that will do little to address the misleading terminology and sensational narratives that plague both public and scientific communications from the astrobiology community."

References

External links

*{{cite web , title=NASA Astrobiology , url=https://astrobiology.nasa.gov/research/life-detection/ , website=astrobiology.nasa.gov , access-date=10 February 2025 , language=en-EN Astrobiology