The search for life beyond Earth is one of the most significant discoveries in the history of science. With hundreds of millions of potentially habitable planets in the Milky Way galaxy, astronomers are using powerful space telescopes to look for molecular indicators of biology in the atmospheres of these planets.
However, detecting life beyond Earth is a challenging task. In 2025, a paper claimed to detect a signature of life on K2-18b, but most scientists remain skeptical due to the lack of strong evidence and repeatability.
To be considered a true discovery, a result must meet three crucial criteria: measuring a meaningful and important quantity, detecting a strong signal, and being repeatable. The detection of dimethyl sulfide in K2-18b’s atmosphere is intriguing, but its significance of 3-sigma is relatively low compared to the “gold standard” of 5-sigma.
The discovery of life on Mars has also been met with skepticism due to lack of strong evidence and repeatability. Previous claims of finding life on Mars, such as the alleged microfossils in the Martian meteorite ALH 84001, have been debunked by scientists.
Astronomers are still searching for definitive evidence of extraterrestrial civilizations, including the detection of microbial life on Mars or an exoplanet. The search for extraterrestrial intelligence (SETI) has yielded some intriguing signals, but none have been confirmed or repeated.
The scientific method requires a high bar of evidence before making a discovery. Astronomers must be cautious when interpreting data and verify results through independent corroboration. By setting a high standard for evidence, scientists can increase confidence in their discoveries and avoid false claims.
Source: https://theconversation.com/extraordinary-claims-require-extraordinary-evidence-an-astronomer-explains-how-much-evidence-scientists-need-to-claim-discoveries-like-extraterrestrial-life-254914