A new study proposes a different way to search for life beyond Earth without depending on specific biosignatures. Instead of looking for one clear sign of biology on a single planet, the researchers argue that life may be easier to detect through patterns shared across many planets. Their findings, published in “The Astrophysical Journal”, introduce a broader framework for astrobiology when conventional biosignatures are weak, ambiguous, or misleading.

A major problem in the search for extraterrestrial life is that many supposed biosignatures, such as certain atmospheric gases, can also be produced by non-living processes. Technosignatures may seem more reliable, but they require strong assumptions about intelligent life and its behavior. To avoid these limitations, the team explored a more flexible idea: life might reveal itself through its large-scale effects on groups of planets rather than through one definitive signal.

This method is described as an “agnostic biosignature” because it does not depend on knowing exactly what life is or how it works. It relies on two general assumptions: life can spread between planets, possibly through panspermia, and it can gradually alter planetary environments.

Using agent-based simulations, Harrison B. Smith of the Earth-Life Science Institute at the Institute of Science Tokyo and Lana Sinapayen of the National Institute for Basic Biology modeled how life could spread through star systems and change planetary traits. They found that if life spreads and reshapes environments, it can create measurable statistical links between where planets are located and what they look like. The concept behind the model is simple: life can travel to and terraform planets around other stars. In doing so, the planet that life travels to becomes more similar to the planet it came from. In this example, life from a planet resembling Earth travels to a red planet. The process plays out again and again. Each time, after being terraformed, a planet becomes more “Earth-like” than would be expected from random chance, given the locations of the planets. However, the focus is not on identifying Earth-like planets. Instead, the aim is to identify any group of planets that are more similar to each other than would be expected by chance, and are localized in space. This technique is agnostic: it does not require making assumptions about habitability or passing judgment on the “kinds of planets” that are amenable to life.

The team also showed that this method can help identify which planets are most likely to host life. By grouping planets according to observable features and spatial relationships, they could highlight the most promising targets for future study while reducing false positives and making better use of limited telescope time.

For more details, read the full article by National Institute for Basic Biology.