Nevertheless, it moves If it moves, its probably alive: Searching for life on other planets Scientists find a way to look for alien life that doesn't need elaborate equipment. Jacek Krywko Feb 12, 2025 7:20 am | 0 If there's life on other planets in our Solar System, it probably won't be this obvious. If there's life on other planets in our Solar System, it probably won't be this obvious. Story textSizeSmallStandardLargeWidth *StandardWideLinksStandardOrange* Subscribers only Learn moreThe search for extraterrestrial life has always been a key motivator of space exploration. But if we were to search Mars, Titan, or the subsurface oceans of Europa or Enceladus, it seems like all we can reasonably hope to find is extremophile microbes. And microbes, just a few microns long and wide, will be difficult to identify if were relying on robots working with limited human supervision and without all the fancy life-detecting gear we have here on Earth.To solve that problem, a team of German researchers at the Technical University in Berlin figured that, instead of having a robot looking for microbes, it would be easier and cheaper to make the microbes come to the robot. The only ingredient they were lacking was the right bait.Looking for movementMost ideas we have for life detection on space mission rely on looking for chemical traces of life, such as various metabolites. Most recent missions, the Perseverance rover included, werent equipped with any specialized life-detecting instruments. On Mars, the focus was on looking for signs of possible ancient lifefossils or other traces of microbes, says Max Riekeles, an astrobiologist at the Technical University Berlin. The last real in-situ life detection missions were performed by Viking landers, which is quite a while back already,We didnt fit more advanced instruments that could reliably look at chemical biosignatures of microbes living on Mars on the most recent mission because such instruments would add too much mass, boost energy consumption, and require additional computing power. So, Riekeles and his colleagues suggested a much simpler and lighter life detection system based on the most obvious biosignature of them all: motility. When you see something move on its own, you can tell its alive, right?But how do you get an alien microbe moving? From previous research, Riekeles knew most microbes, even those living in extreme environments, are attracted to L-serine, an amino acid used by organisms on Earth to build proteins. The microbes sense the presence of L-serine in their surroundings and move toward it, a behavior known as chemotaxis. Also, there seems to be evidence L-serine was found outside of Earth, and it was present in the Martian environment, Riekeles said.Once the bait was sorted, the team chose its test subjects, the microorganisms chosen to play the part of aliens were extremophile bacteria. They picked several, including Bacillus subtilis, which can survive in temperatures reaching 100 C, and Pseudoalteromonas haloplanktis, which lived in the cold waters of Antarctica. The third organism they used was Haloferax volcanii, an archaeon inhabiting extremely saline environments like the Dead Sea. This one was especially interesting to us because we know from spectral evidence that there seems to be a lot of salt on Mars,Riekeles explains.The researchers used glass containers divided into two chambers separated by a barrier. Samples with microbes ended up in one chamber, the L-serine in the other, and the barrier, formed using a gel, was formulated to be permeable to microbes but impenetrable by abiotic particles. ThenRiekeles and his colleagues watched the containers using a rather simple microscope, looking for blobs of microbes forming in the L-serine chamber. Blobs were observed in experiments with all three microbes, which happily relocated to L-serine chambers within an hour and a half or so.Movement detected; life confirmed.The problem is a life-detection system like that should work well, provided those possible alien microbes look like microbes on Earth. But what if alien life proves a bit more surprising?Baiting the unknownOn the face of it, Riekeles idea to bet on motility as a biosignature seems quite robust against possible different chemistries and natures of alien life. You can imagine life that is not similar to our life but still evolved motility just because motility is super useful in terms of evolutionit evolved multiple times independently here on Earth, Reikeles says. But the limitations start to appear when you plunge deeper into details.The most obvious one is that only around 40 percent of prokaryotes on Earth can move. If that percentage holds true for alien worlds, well be missing more than half of possible extraterrestrial microbes right off the bat. And even microbes that can move might prove a bit tricky.The second issue is the unknown size of alien microbes. Riekeles and his colleagues knew how big the organisms they studied were beforehand, so the permeability of membranes separating the chambers was fine-tuned to let these microbes through. But what if the aliens turned out to be a bit larger than expected? At this point we are not sure what kind of membrane would be best for Mars missions. We also dont know how our membranes would perform in Mars temperatures and atmosphere, Riekeles acknowledges. Designing a more universal membrane will be its own research project.Even if the membrane issue gets sorted out, there is still the question of possible different chemistries of alien life starting with left-handed chirality. Life on Earth is based on left-handed amino acids. This is why Riekelesused L-serine, rather than R-serine in his experiments. But what if life on alien worlds evolved to choose the right-handed variety? Should we include R-serine too when sending missions to Mars or elsewhere, just in case?And how do you bait life that is completely, not just slightly alien? what if we assume, after the molecular simulation experiments done at Cornell University back in 2015, that cell membranes made of vinyl cyanide could form in the liquid methane found on Saturns moon Titan? The answers lie in the final design of the life-detecting instrument that Riekeles has in mind.The optimal way of doing it for a Mars mission would be to come up with a system where a sample is in the middle, surrounded by a variety of amino acids with different chirality,Riekeles says. He expects that coming up with baits for life with different methane-based biochemistry should be possible. But we havent explored that yet. We need to test way more organisms and see what substances are working for the most of them. There is no one-size-fits-all solution, unfortunately, Riekeles says. The next step for Riekeles life detection system will be testing it in a Mars simulation chamber replicating atmospheric conditions, temperature, irradiation, and the regolith properties present on the Red Planet.Frontiers in Astronomy and Space Sciences, 2025. DOI: 10.3389/fspas.2024.1490090Jacek KrywkoAssociate WriterJacek KrywkoAssociate Writer Jacek Krywko is a freelance science and technology writer who covers space exploration, artificial intelligence research, computer science, and all sorts of engineering wizardry. 0 Comments