For decades, the search for life on exoplanets has yielded nothing but silence. What if humanity’s search for life on other planets returns no hits? A team of researchers from ETH Zurich and the SETI Institute tackled this question by considering what could be learned about life in the universe if future surveys detect no signs of life on other planets.
The study, published in The Astronomical Journal, relies on Bayesian statistical analysis to establish the minimum number of exoplanets that should be observed to obtain meaningful answers about the frequency of potentially inhabited worlds. Accounting for uncertainty, the team found that a large survey could confidently conclude that fewer than 10 to 20% of similar planets harbor life.
This type of finding would enable researchers to put a meaningful upper limit on the prevalence of life in the universe, an estimate that has remained out of reach so far. However, there’s a catch: every observation comes with a certain level of uncertainty, which affects the robustness of the conclusions drawn from the data.
To address this, the study highlights the importance of asking the right questions and how confident we can be in seeing or not seeing what we’re searching for. The team emphasizes that even advanced instruments require careful accounting and quantification of uncertainties and biases to ensure that outcomes are statistically meaningful.
The researchers also studied how assumed previous knowledge affects the results of future surveys, comparing the outcomes of Bayesian and Frequentist approaches. While the influence of chosen priors is found to be limited in this scenario, the two frameworks yield comparable results, showing that distinct approaches provide a complementary understanding of the same dataset.
Ultimately, this work shows why it’s essential to formulate the right research questions, choose the appropriate methodology, and implement careful sampling designs for a reliable statistical interpretation of a study’s outcome. Even if we don’t find life, we’ll be able to quantify how rare—or common—planets with detectable biosignatures really might be.
Source: https://phys.org/news/2025-04-life-exoplanets.html