Stars’ Age, Size Key for Alien Life Search

New method helps pinpoint planets most likely to host life.

Scientists have developed a new way to compare which distant stars might host alien life. This helps future space missions pick the best targets to find signs of life.

The researchers wanted to know how a star’s age, size, and other features affect the chances of finding life on its planets. They looked at which factors most influence these "biosignature yields" (the likelihood of finding evidence of life).

The Computer Model Investigated

They created a computer model that calculates the chance of finding life around a star. This model considers how a star's "habitable zone" (the area around a star where conditions are right for liquid water) changes over time. They tested three ways life might appear.

The study looked at many stars, ranging from 0.4 to 1.5 times the size of our sun and from 200 million to 10 billion years old. They also used two known stars, 55 Cancri and θ Cygni, as examples. Their model followed how stars evolve and how long their planets stay in the habitable zone.

Key Findings

The team found that deciding whether smaller K stars or larger F stars are better for finding life depends on the specific model used. For instance, stars that are young and bright but cannot support life for a very long time might seem like good candidates at first glance. They also learned that finding life depends on whether life can start on "Cold Start" exoplanets (planets that begin outside the habitable zone and later move into it).

The study showed that just looking at a star’s current habitable zone can be misleading. Using only this present zone suggested that big, older stars near the end of their lives are best. But considering a star's full history changes this view.

"The relative biosignature yield is meant to be compared between potential direct imaging target stars in order to determine which are more likely to host biosignatures."

— Tuchow & Wright

Limitations and Future Impact

The researchers noted some limits to their work:

• It is hard to know a star’s exact age and how many planets orbit it.
• Their models also made some simple assumptions.
• Whether life can start on Cold Start planets is still a big question.

This new framework will help guide future space missions like HabEx and LUVOIR. These missions need to consider a planet's full history of habitability, not just its current state, to find life elsewhere in the universe. Choosing the right stars now saves time and resources later.