Signs of extraterrestrial life may have been ignored by researchers for decades, say a team of astrobiologists, warning of the potential pitfalls of false negatives in the search for ET.

In a recent paper in Nature Astronomy, researchers at Utrecht University argue that poorly designed tests for life elsewhere in the cosmos are a great waste of science funding.

Astrobiology is a specialized field dedicated to discovering the origins of life and detecting life on other planets, yet it remains ambiguous in its conclusions.

False Extraterrestrial Signals

“We should be aware of these false-negative results,” says lead author Inge Loes ten Kate, professor in astrobiology at Utrecht University and the University of Amsterdam. “It means there are shortcomings in recognizing the existence of life. These shortcomings are not yet high on the research agenda.”

The researchers argue that while false positives are well considered in the astrobiology field, potential false negatives, in which existing extraterrestrial life may not appear present, are largely overlooked, to the detriment of the field.

The researchers identified three primary reasons why the search for extraterrestrial life may lead to false negatives. The first is that ancient life on distant worlds may not have been preserved, leaving no remnants left to uncover, even if something once lived. The second two are related; the signals of life on some world may be extremely faint, and our current level of technology may not be advanced enough to detect them. 

“There are several life-detection instrument concepts in development for Mars and even for icy moons that so far have not yet been selected for a mission that I would love to see fly,” Professor ten Kate told The Debrief. “Even though we will always run the risk that those instruments will not find life, whether it is there or not.”

Targeting the Extraterrestrial

“We therefore advocate for the development of a targeted research strategy that systematically addresses these risks, in which we must combine laboratory experiments with modeling research and fieldwork,” ten Kate explained. “Space missions and instruments are designed to detect potential signs of life, but the risk of overlooking something is not taken into account.” 

“The search for signs of life should go hand in hand with better-defined questions and testable hypotheses to justify specific measurement or observation targets,” ten Kate continued.

The researchers favor using artificial intelligence tools to recognize patterns in extraterritorial data, which might identify elements missed by the human eye, and then apply them to future observations. They also note that failing to identify evidence of life may lead to long-term mistakes, such as dismissing objectives and instruments too hastily. They compare this to a person looking at a rock from above, unaware that bugs live beneath it, and, down the line, resource extraction could destroy the rock and the bugs with it.

Possibilities for Life Elsewhere

The Utrecht researchers say that much work remains to be done theorizing what sort of life may exist in the cosmos, what types of environments that life could persist in, and what external signals it should produce. A recent example the team is interested in is an unusual oxidation noted in a Martian rock last year, which bore intriguing similarities to finds on Earth, the only planet known to harbor life.

“On Earth, we only see such differing oxidation as a result of the presence of life,” ten Kate said. “But does that necessarily mean that we are dealing with life in an extraterrestrial context?”

The team says that to better understand this promising Martian discovery, astrobiologists will have to refine their understanding of geochemistry in an extraterrestrial environment before sending a crewed mission to investigate the Red Planet.

If there were life, and it were hidden, ten Kate argues, “there would be a high likelihood of the crew unknowingly killing that Martian life.”

“Although this hypothetical Martian life might ‘only’ be unicellular, like bacteria, in my opinion, we do not have the right to kill it, not even accidentally,” ten Kate concluded. “This is, of course, an ethical dilemma, and I know not everybody would agree.”

The paper, “False Negatives in the Search for Extraterrestrial Life,” appeared in Nature Astronomy on May 21, 2026.

Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.

Earth has many unique features for a planet, such as a magnetic field, a large moon, and plate tectonics. It’s also the only planet we know of that harbors life. These facts form the basis of the Rare Earth hypothesis, which posits that we haven’t found aliens because other planets in the Galaxy probably don’t have all the right conditions for life. 

Another characteristic of Earth is that about 30% of its surface is land and about 70% is ocean. Recently, Columbia University Assistant Professor David Kipping investigated whether the proportion of Earth’s surface covered by dry land versus ocean, or its land fraction, is another reason Earth is habitable not only for simple single-celled organisms, but also for intelligent species like humans. 

To test this hypothesis, Kipping created 4 statistical models of planets with different land fractions that intelligent aliens could potentially evolve on. First, he created an equation to describe the likelihood that a planet in its star’s habitable zone has a particular land fraction, known as a probability distribution. Kipping weighted this probability distribution toward the extreme ends, making it more likely that a planet would be covered by a single huge landmass or a single vast ocean than by a mix of both, as on Earth. 

Kipping then incorporated this land fraction probability distribution into his statistical models to calculate the probability that a random planet will have that land fraction and host intelligent life. The 4 scenarios Kipping tested were: 1) that intelligent life is more likely to emerge on land-dominated planets, 2) that it’s more likely to emerge on ocean-dominated planets, 3) that it’s more likely to emerge on planets with roughly equal amounts of land and ocean, and 4) that its emergence is independent of a planet’s land fraction. 

As a first step in determining the kinds of planets intelligent aliens would tend to emerge on, Kipping used each model to predict the probability that intelligent life would emerge on a planet with the same land fraction as Earth. He then compared these probabilities by calculating the ratios between each value. Because Earth is the only known planet with intelligent life, a model that predicted a greater probability for humanity’s existence on Earth would be more likely to reflect reality.

Kipping considered it strong evidence that a given model was more realistic than another if the ratio between 2 of them was greater than 10, meaning one model was 10 times more likely to predict the existence of Earth and humanity. Kipping found that no comparison of any 2 models passed this threshold. However, the models assuming that intelligent life prefers ocean-dominated planets or planets with a land-ocean balance were 2.5 and 3 times more likely to predict the existence of humanity than the model assuming that intelligent life prefers land-dominated planets. Additionally, the model assuming that intelligent life prefers a land-ocean balance was always more likely to predict humanity than any other model, though marginally. 

Kipping also addressed whether finding more planets with intelligent life would affect which model was deemed most realistic, for example, if scientists discovered conclusive evidence of life on Mars in its distant past. Here, Kipping identified 2 complications. First, it’s uncertain how much of Mars’s surface was once covered by water – some estimate it had a land fraction as high as 81%, while others estimate it was as low as 25%. Second, proving that Mars once had life would not prove it once had intelligent life.

Regardless, Kipping reran the models assuming that ancient Mars had a land fraction comparable to Earth’s. Adding this second data point produced ratios similar to those in the earlier Earth-only calculations, meaning it still didn’t make any single model 10 times more likely to predict the existence of humans and Martians, respectively. 

Kipping then took the 10-times threshold and reversed the calculations to find what conditions would exceed it. In doing so, he calculated that astronomers would need to find 14 other planets with intelligent life and known land fractions to robustly determine whether intelligent life is more likely to occur on desert planets, ocean planets, balanced planets, or without bias.

Kipping concluded that he can’t yet definitively state whether there is something special about Earth’s land fraction when it comes to producing intelligent species. However, Earth’s existence would suggest that intelligent life is unlikely to favor extreme desert planets, so the Milky Way probably isn’t filled with Tatooines and Jakkus. And while his analysis doesn’t debunk the Rare Earth hypothesis, it does undermine the argument that Earth’s ocean size explains why Earth is rare. 

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Most people think of Mars as a big red dustball, but researchers recently found Martian mineral deposits suggesting it was once warm and humid. The team used the Compact Reconnaissance Imaging Spectrometer aboard NASA’s Mars Reconnaissance Orbiter to analyze specific wavelengths of visible and near-infrared light from minerals on Mars’s surface to determine their chemical composition from afar.

Past researchers identified layered silicate minerals, called clays, across the Martian surface. Clays form when water interacts with rock, and record the amounts and chemical compositions of the waters that formed them. As water interacted with Martian surface rocks, it picked up more mobile elements like magnesium and iron and carried them to lower depths in the Martian soils, while less mobile elements like aluminum stayed in place. This process, called leaching, created 2 distinct layers of clays in the Martian rocks. 

Scientists have proposed 2 main hypotheses for how these layered clays formed on Mars. The first is that they formed through underwater leaching in pools or lakes sometime in Mars’ past. The second is that they formed across the Martian surface, where a widespread humid environment provided the moisture needed to leach them. 

To evaluate these hypotheses, a team led by researchers at Purdue University recently estimated the “true” thicknesses of Martian clay layers with a method scientists had previously only used on Earth. Rock layers containing clays can become tilted, making them appear thicker or thinner than they actually are. To address this discrepancy, the team used the High Resolution Imaging Science Experiment (HiRISE) tool on the Mars Reconnaissance Orbiter to create high-resolution elevation maps of the Martian surface. Then they combined these maps with surface composition data from the Compact Reconnaissance Imaging Spectrometer to create 3D composition maps. 

Using the 3D composition maps, the researchers found where each clay layer was exposed at the surface and traced it underground to estimate an angle of tilt. They then used trigonometry to calculate the true thicknesses of each clay layer. They analysed 46 regions across the Martian surface, and found that the combined thickness of both clay layers was around 20 to 680 feet (6 to 200 meters), with an average of about 190 feet (60 meters). That’s a maximum thickness as high as a 60-story building! 

Next, the researchers tested the extent of the clay deposits in a large ancient Martian valley known as the Mawrth Vallis Region. They focused on this region because it had large elevation changes, and scientists in the past had already collected high-resolution chemical composition and elevation data there. 

They explained that if the clay layers were restricted to the lowest parts of the valley where water once existed, and had changing thicknesses and boundaries between layers, this would provide strong evidence in favor of the “underwater leaching” hypothesis. In contrast, if the clay layers were more widespread, with consistent layer boundaries and thicknesses, this would provide strong evidence of a humid surface environment, in favor of the “surface leaching” hypothesis. 

The researchers found that the clay layers extended beyond the lowest parts of the valley and had consistent layer boundaries across more than half a mile (about a kilometer) of elevation change. Thus, they concluded that the clay layers formed by surface leaching in a humid environment. 

These findings conflict with climate models of early Mars, which generally suggest that the Martian surface rarely got above freezing temperatures. To address this discrepancy, the team proposed that these deposits could have formed over a long period of time rather than in a consistently warm and wet environment. If the surface was frozen most of the time, but got above freezing in short bursts, these clay deposits could still have formed, just over a much longer time period. In this case, the Mars climate models and the researchers’ findings would agree.

The researchers acknowledged that their study has some limitations, particularly regarding the sparse sample locations. Though they found strong evidence for a widespread humid environment on early Mars, more in-depth studies of locations like Mawrth Vallis could better constrain the specific surface environmental conditions under which these clays formed and potentially reconcile their data with Martian climate models.

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