Using advanced statistical modeling, a team of researchers from ETH Zurich, Seti Institute, and University ‘Tor Vergata’ Yonversity investigated how many exoplanets should be observed and understood before declaring that life beyond Earth is common or rare.
Future telescopes will investigate mild terrestrial exoplanets to estimate the frequency of habitable or inhabited worlds. Angerhausen et al. It aims to determine the minimum number of exoplanets required to draw statistically significant conclusions. Particularly for null results (i.e., no detection). Image credit: Sci.News.
In science, not being able to find anything can bring important insights.
When scientists look for life on exoplanets, they often focus on certain characteristics, such as water, gases like oxygen and methane, which may exhibit biological activity.
But what if scientists can’t find these features? Can we learn meaningful things about how ordinary life exists in the universe?
“Even one positive detection changes everything, but up until then we need to make sure we are learning as much as possible from what we can’t find,” said Dr. Daniel Angerhausen, researcher at ETH Zurich and SETI Institute.
New research shows that if scientists look at 40-80 planets and can’t find any signs of life, they can confidently conclude that less than 10-20% of similar planets have life.
However, this depends heavily on how certain we are for each observation.
These discoveries allow scientists to set meaningful caps on the prevalence of living in the universe.
Furthermore, if there is only 10% of planets in the Milky Way alone that have some form of life, it could still be more than 10 billion planets.
“This kind of outcome would be a turning point,” Dr. Angerhausen said.
“Even if life is not found, ultimately we can quantify planets that are truly rare or common with planets with detectable biosignatures.”
The findings will have a direct impact on future missions such as NASA’s Habitable World Observatory (HWO) and European-led large-scale interferometers on exoplanets searching for life.
These missions will study dozens of Earth-like planets by analyzing the planet’s atmosphere for water, oxygen, and even more complex biosignature signs.
Research shows that the number of observed planets is large enough to draw critical conclusions about the likelihood and prevalence of life in the galaxy.
However, this study points out that even with advanced equipment, these studies should carefully account for uncertainty and bias, and develop frameworks to ensure statistically meaningful results.
One important insight from this study is that uncertainty in individual observations, such as false negatives, can significantly impact conclusions.
“It’s not just the number of planets we observe. It’s about how confident we are to see what we’re looking for or not,” Dr. Angerhausen said.
“If we are not careful and confident in our ability to identify life, even large-scale research can lead to misleading consequences.”
The study will be published in today’s Astronomy Journal.
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Daniel Engerhausen et al. 2025. What if nothing is found? Bayesian analysis of null statistics in future exoplanet habitability and biosignature investigations. AJ 169, 238; doi:10.3847/1538-3881/adb96d
Source: www.sci.news
