One of the many frustrating factors that complicate the search for extraterrestrial life is the time and resources spent analyzing false signals. Molecules such as amino acids and fatty acids, which are commonly associated with signs of biological life, can also form in places where life has never existed.
Amino acids have turned up in meteorites, and fatty acids can develop in deep space without any biological input. This overlap between biological and nonbiological chemistry is a recurring challenge for astrobiologists.
Now, a new study in Nature Astronomy suggests that, instead of searching for new types of molecules, scientists should adopt a different approach. Researchers from the Weizmann Institute of Science and the University of California, Riverside, say that biological life leaves a statistical signature that can be found in the molecular data spacecraft are already collecting.
“We’re showing that life does not only produce molecules,” said Fabian Klenner, a UC Riverside assistant professor of planetary sciences and co-author of the study. “Life also produces an organizational principle that we can see by applying statistics.”
While amino acids and fatty acids are essential for life on Earth, their presence does not always indicate the presence of life. Scientists have found these molecules naturally occurring in meteorites and have also reproduced them in lab simulations of space conditions. Their existence alone is not enough to confirm the existence of life in areas where they are found.
This makes things difficult for planetary scientists. As missions to Mars, Europa, Enceladus, and other intriguing worlds return more detailed chemical data, the real challenge is determining whether those signals indicate signs of life or of chemistry occurring in the absence of biology.
“Astrobiology is fundamentally a forensic science,” said author of the study Gideon Yoffe, a postdoctoral researcher at the Weizmann Institute. “We’re trying to infer processes from incomplete clues, often with very limited data collected by missions that are extraordinarily expensive and infrequent.”
The researchers adapted a concept from ecology to measure biodiversity. Ecologists often look at two main properties: the richness or number of different species present, and the evenness of their distribution. Healthy ecosystems usually have both high diversity and even distribution, while degraded environments do not.
Yoffe first came across these diversity metrics during his doctoral studies in statistics and data science, where they were used to analyze complex datasets unrelated to biology. He later wondered if the same approach could help distinguish living chemistry from nonliving chemistry.
To test this idea, the team analyzed about 100 datasets of amino acids and fatty acids from sources including microbes, soils, fossils, meteorites, asteroids, and lab-made samples. They found that biological samples had a clear statistical pattern: their amino acid mixtures were more diverse and more evenly spread than those in nonliving material. For fatty acids, the trend was the opposite. Living organisms distribute fatty acids less evenly than nonliving processes do. The researchers believe this difference is a basic sign of biosynthesis.
One surprising result was that the method even worked on old, degraded samples. Fossilized dinosaur eggshells buried for tens of millions of years still showed traces of this statistical pattern.
“That was genuinely surprising,” Klenner said. “The method captured not only the distinction between life and nonlife, but also degrees of preservation and alteration.”
The timing is key. NASA’s Europa Clipper is already on its way to Jupiter’s moon Europa. Scientists are currently planning missions to Saturn’s moon Enceladus. The Mars Perseverance rover is still collecting samples that could one day be brought back to Earth. Each of these missions will produce the molecular data needed for this new approach.
Notably, this method does not require any special instruments. It uses the relative amounts of different molecules, which current and planned mission equipment can already measure. This means the technique could be used on data from past and future missions. The researchers caution that a positive statistical signal does not prove life existed in a sample. Instead, it would be one piece of evidence that suggests life may have been present.
“Any future claim of having found life would require multiple independent lines of evidence, interpreted within the geological and chemical context of a planetary environment,” Klenner said.
The team sees their method as one more tool in the growing set of techniques used to search for life beyond Earth. If several different methods all point to the same sample, such as statistical diversity, chemical makeup, isotopic ratios, and geological context, it becomes much more difficult to dismiss the result.
“Our approach is one more way to assess whether life may have been there,” Klenner said. “And if different techniques all point in the same direction, then that becomes very powerful.”
Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds an MBA, a Bachelor of Science in Business Administration, and a data analytics certification. His work focuses on breaking scientific developments, with an emphasis on emerging biology, cognitive neuroscience, and archaeological discoveries.
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The post Scientists used a method from ecology to identify whether icy moons could hold conditions for life appeared first on Astronomy Magazine.
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The post Could aliens ever visit Earth? appeared first on Astronomy Magazine.
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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