How Many Planets Are Enough?

According to researchers, surveying between 40 and 80 Earth-like exoplanets and finding no signs of life—a so-called "perfect" null result—could still offer valuable insights. Such a result would suggest that fewer than 10 to 20 percent of similar planets in the galaxy harbor life. Given the sheer number of stars in the Milky Way, even that 10 percent could mean as many as 10 billion potentially inhabited worlds. So, even without discovering life, scientists could finally place a meaningful upper limit on how common it might be across the cosmos—something that’s been frustratingly out of reach until now.

Figure 1. The Power of Nothing: How Emptiness Informs the Search for Life.

However, there’s a caveat. Even a “perfect” null result comes with uncertainty, which affects how confident we can be in the conclusions. One source of uncertainty, known as interpretation uncertainty, comes from the risk of false negatives—cases where life exists but remains undetected. Another, called sample uncertainty, stems from potential biases in the types of planets chosen for study. If some planets in the sample aren’t truly capable of supporting life, the results could lead us astray. Recognizing and accounting for these uncertainties is crucial to making solid scientific judgments from upcoming planet-hunting missions. Figure 1 shows The Power of Nothing: How Emptiness Informs the Search for Life.

Asking the Right Questions

“It’s not just about how many planets we observe—it’s about asking the right questions and understanding how confident we can be in detecting, or not detecting, the signs we’re looking for,” explains Angerhausen. “If we’re not careful, and we overestimate our ability to recognize signs of life, even a large survey could end up leading us astray.”

These concerns are especially relevant for upcoming missions like the international Large Interferometer for Exoplanets (LIFE), led by ETH Zurich. LIFE aims to investigate dozens of exoplanets with Earth-like mass, size, and temperature by analyzing their atmospheres for key biosignatures such as water vapor, oxygen, and more complex indicators of life. Encouragingly, Angerhausen and his team believe that the planned number of observations will be sufficient to draw meaningful conclusions about how common life might be in our galactic neighborhood.

Bayesian vs. Frequentist Perspectives

Angerhausen and his colleagues also explored how assumptions about prior knowledge—referred to as priors in Bayesian statistics—can shape the results of future exoplanet surveys. To do this, they compared outcomes from the Bayesian framework with those from the Frequentist approach, which relies solely on observed data and does not incorporate prior assumptions. For the sample sizes anticipated in missions like LIFE, they found that the influence of priors in Bayesian analysis is relatively limited. In fact, both statistical methods produced similar conclusions under these conditions.

“In applied science, Bayesian and Frequentist statistics are often viewed as rival schools of thought. But as a statistician, I prefer to see them as complementary tools for understanding the world and interpreting probabilities,” says co-author Emily Garvin, a PhD student in Quanz’s group. Garvin focused on the Frequentist analysis, which played a key role in validating the team’s findings and checking the robustness of their assumptions. “Depending on a survey’s specific scientific goals, different statistical methods may be better suited to deliver accurate and reliable insights,” she adds. “Our aim was to show how different approaches can enrich one another and offer a broader roadmap for interpreting complex data.”

The Power of Just One Discovery

This research underscores the importance of asking the right questions, selecting appropriate methods, and designing careful sampling strategies to ensure statistically reliable conclusions. “A single positive detection would change everything,” says Angerhausen. “But even if we don’t find life, we’ll still gain the ability to quantify how rare—or how common—planets with detectable biosignatures might truly be.”

Source: SciTECHDaily

Cite this article:

Priyadharshini S (2025), No Signs, Big Revelations: How Null Results Shape Our Search for Life, AnaTechMaz, pp.334