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We don't actually know if aliens exist, but if they do, their cells probably have a special type of membrane. And that knowledge alone tells us where we can look for them, and maybe even what they'll be like. Hi, I'm David, and this is Minute Earth. There are lots of different ways scientists can search for life on other planets. They can listen for radio signals from alien civilizations. They can scan distant atmospheres for the chemical fingerprints life leaves behind, and they can send spacecraft to sample places in our own solar system where life might be hiding. Or they can search for places that have the right conditions for a particular type of membrane to form. This last one is actually a pretty powerful tool for
zeroing in on possible extraterrestrial life, because virtually every cell on Earth is wrapped in a membrane that keeps its contents inside, built up a gradient by piling charged particles on one side, and then captures energy as those particles flow back through to the other. These membranes, we can call them electrochemical membranes, are so fundamental to life that many experts think that extraterrestrial life will likely have them, too. On Earth, electrochemical membranes are formed from a specific set of elements: carbon, hydrogen, oxygen, nitrogen, and phosphorus, which can form molecules that, in the presence of liquid water, assemble into, well, membranes. And those membranes, in turn, form the
foundation of life on Earth. So, one way to find extraterrestrial life is to look for other worlds that have those same elements and the liquid water that would allow them to self-assemble and some sort of energy to power the life forms. And there are two of those worlds relatively nearby. Saturn's moon Enceladus has all of those elements and liquid water, though the ocean is buried under a thick shell of ice. So, the membranes crucial to life could potentially form on Enceladus, but without direct sunlight, there's not much energy available. Any life that formed there would likely have to rely on the trickle of energy coming from hydrothermal vents on the ocean floor. So, I imagine that any life there would
be small and live right next to those vents. Jupiter's moon Europa also has all five of those membrane-building elements and a liquid ocean under an icy shell. But unlike energy-poor Enceladus, Europa is constantly being bombarded by radiation from Jupiter and experiences much more tidal heating as it gets pushed and pulled by the massive planet. So, if there is life on Europa, perhaps it's faster moving because it has more access to that energy. And then there's K2-18b, a planet about 120 light-years away from us. From spectroscopy, we're pretty sure that it has at least three of the required elements to build Earth-like electrochemical membranes, and it may even have liquid water. But,
it's also surrounded by a thick layer of hydrogen gas, which for complicated chemistry reasons some scientists speculate would lead not to the development of lots of individual membranes, but instead one big one. So, that makes me envision alien life on K2-18b that's not multiple organisms, but instead a single giant film that covers the entire world. And life may not actually be limited to worlds with exact Earth-like chemistry because scientists think that in some cases electrochemical membranes might be able to form from slightly different ingredients. The clouds surrounding Venus, for example, have no liquid water. So, Earth-like membranes couldn't form there, and even if they did, the
clouds are made of concentrated sulfuric acid, which would destroy those membranes on contact. What scientists have discovered, though, is that electrochemical membranes built with sulfur can actually self-assemble and survive in strong acid. So, any life on Venus would probably have to form inside droplets of sulfuric acid. And because those droplets would have access to plenty of energy from sunlight as they floated up and down in the clouds, I picture excited aliens bopping around in their little acid bubbles. Again, we still don't know whether aliens exist, but focusing on the likelihood that they'll have electrochemical membranes doesn't just tell us where to look. It also hints that whatever we find could be deeply weird.
