A new space mission concept led by researchers at ETH Zurich aims to determine how common life is in the universe — even if no signs of life are detected. Known as LIFE (Large Interferometer For Exoplanets), the proposed mission would use four space telescopes flying in formation around a central combiner spacecraft to examine rocky planets located in their stars' habitable zones.

Advertisment

The LIFE mission intends to investigate the atmospheres of exoplanets for biosignatures — chemical indicators of life such as oxygen, water vapour, methane, and others. Using a technique called nulling interferometry, the telescopes would cancel out the light of host stars, allowing the faint signals from orbiting planets to be observed. Although the telescopes would not directly image the planets, they would perform mid-infrared spectroscopy to identify atmospheric molecules.

Currently, LIFE remains a mission concept and has not been adopted by any space agency. However, scientists at ETH Zurich have been examining what such a mission could reveal even in the absence of a positive detection.

Using Bayesian statistical modelling, the team calculated how many Earth-like exoplanets the mission would need to survey to make a meaningful statement about the rarity of life. According to their analysis, if LIFE observed between 40 and 80 planets without detecting any biosignatures, it could suggest — with statistical confidence — that fewer than 10 to 20 per cent of similar planets in the galaxy host life.

Advertisment

The study highlights the importance of the chosen statistical approach. Bayesian statistics uses existing knowledge to refine probability estimates, while frequentist statistics relies on large samples and repeated trials. The researchers applied both methods to ensure robustness in their conclusions and found similar results from both approaches.

The team acknowledges that uncertainties remain. Biosignatures may be present but undetectable, or some planets might be misclassified as habitable. These factors could affect interpretations of the data.

Emily Garvin, a doctoral researcher at ETH Zurich, noted that different survey goals may require tailored statistical methods. The study presents a framework for adopting multiple approaches to interpret findings from future space-based observations.

Advertisment

Even if LIFE does not detect biosignatures, its observations could place upper limits on how common inhabited planets are — contributing to a broader understanding of life's distribution in the universe. The findings were published in The Astronomical Journal on 7 April.