What null results in the search for life could still reveal

What null results in the search for life could still reveal
by Clarence Oxford
Los Angeles CA (SPX) Apr 10, 2025

BODY TEXT: What if, after decades of scanning the cosmos with cutting-edge telescopes, we still detect no signs of extraterrestrial life? A new study led by researchers at ETH Zurich, including SETI Institute affiliate Dr. Daniel Angerhausen, explores this possibility and argues that such null results can still offer profound insights. Using Bayesian statistical methods, the researchers aimed to determine how many exoplanets must be studied before scientists can make meaningful statements about the abundance or scarcity of life in the universe.

"Even a single positive detection would change everything-but until then, we need to make sure we're learning as much as possible from what we don't find," said Angerhausen.

Null results, often viewed as disappointing, can actually inform researchers about the likelihood of life existing elsewhere. When scientists search for biosignatures-such as oxygen, methane, or water vapor-and find none, those absences can help define statistical limits on life's prevalence. According to the study, if life is absent from 40 to 80 carefully selected planets, researchers could infer that fewer than 10 to 20 percent of similar worlds are home to life. This marks a significant step forward in turning absence into information.

Angerhausen explained, "This kind of result would be a turning point. Even if we don't find life, we'll finally be able to quantify how rare - or common - planets with detectable biosignatures really might be."

These findings are especially relevant for upcoming missions like NASA's Habitable Worlds Observatory and the European LIFE project, which aim to study dozens of Earth-like exoplanets. By targeting atmospheric features that might suggest life, these missions could gather enough data to support broader conclusions about planetary habitability.

However, the study also highlights the importance of accounting for observational uncertainty. If instruments fail to detect biosignatures that are present, or if unsuitable planets are misclassified as habitable, the conclusions drawn from these surveys could be misleading. "It's not just about how many planets we observe-it's about how confident we can be in seeing or not seeing what we are searching for," Angerhausen noted.

To improve the reliability of such research, the team recommends refining the questions scientists ask. Rather than seeking a generalized answer to how common life is, researchers might instead ask more targeted questions, such as: What fraction of rocky planets in the habitable zone exhibit specific biosignatures like water vapor, methane, or oxygen?

By designing studies that address these specific parameters and rigorously handling uncertainties, scientists can make null results meaningful. Even in the absence of confirmed alien life, future surveys will help illuminate the conditions that favor habitability, deepening our understanding of life's potential across the galaxy.

Research Report:What if We Find Nothing? Bayesian Analysis of the Statistical Information of Null Results in Future Exoplanet Habitability and Biosignature Surveys