The Fermi Paradox is one of the most puzzling problems about living in our universe. Based on our current understanding of biology and physics, we should see alien civilizations or signs of their existence across the night sky. Yet as far as we can tell, we are alone in the cosmos. Why is this?
One reason that we are not finding alien life is that we are not looking in the right places. Since Earth lifeforms are the only ones we know of, scientists have tended to look for life like ours. Perhaps Earth is unusual, and life flourishes in far stranger places than we ever imagined.
Here are ten places that have been suggested as homes for alien organisms.
Venus is quiet like Earth, or at least Earth if it was sent to hell. Both planets are similar in size and mass, and the surface’s gravity is comparable. Surely this makes it an obvious place to look for life. When astronomers in the early 20th century peered at Venus through their telescopes, all they could see were dense clouds reflecting sunlight. This led some to picture the surface as a tropical and humid swamp teeming with lifeforms. Unfortunately, when space probes explored the planet, they found its surface temperature was hot enough to melt lead, and its toxic atmosphere had a pressure nearly 100 times that on Earth. Not really somewhere to expect life, then.
Except there are parts of the planet that may just harbors organisms. There are places higher in the atmosphere where the pressure is not too great, the temperature is cool enough for liquid water, and there might be less of the ubiquitous sulfuric acid. Single-celled organisms might be able to exist there, caught in the high winds.
One theory is that these organisms could live their lives in two stages. When in the right place, they are active and alive, but if they start falling toward the surface as a droplet forms around them, they go into a tough hibernation state that can survive at lower levels. As they dry out on their descent, they become lighter and are carried back into the habitable zone, where they can become active again.
A recent observation by the ALMA observatory suggested there were high levels of phosphine in the atmosphere of Venus. On Earth, only life is known to form phosphine, so it was suggested it might be coming from Venusian life. Unfortunately, it seems that this detection was mistaken. If life exists on Venus, we’ll have to look harder.
9 Under Ice
One of the reasons astronomers search Earth-like planets in certain orbits around stars is that there is one indisputable fact about life on Earth—it needs liquid water to survive. Too close to a star, and all the water boils. Too far, and it all turns to ice. At least, that was what astronomers thought. Some places outside the habitable zone of our own sun might be concealing vast oceans.
The icy moons of Jupiter, like Ganymede, Europa, and Callisto, are covered with layers of water ice but underneath may be deep reservoirs of water where life could evolve. Europa is only a quarter the diameter of Earth but could have more than four times all the water found in Earth’s oceans under its icy outer crust. It is thought that the massive pressures exerted by Jupiter’s gravity provide the energy to keep this ocean in its liquid form.
We know that life can exist in the deepest and darkest parts of Earth’s seas, and so it is just possible that life found a way to survive on these icy moons. Multiple space probes have been and will be launched toward Jupiter to get a better look at its moons and see if life can be detected.
Comets can be some of the most spectacular sights in our sky. As they plunge from the outer solar system toward the sun, they warm up and blast huge plumes that form illuminated tails behind the comet. Because they have a large amount of water ice, they may have been vital to the formation of life on Earth. It is thought that much of the water on our came from comets colliding with the early Earth. But could life exist on comets themselves?
At first, it seems unlikely. Comets spend the majority of their time far away from the light and warmth of the sun. When at their furthest, temperatures can be just 50 degrees above absolute zero. When at this temperature and with minimal gravity of their own, comets have no atmosphere to speak of. When the Rosetta space mission placed a lander on comet 67P/Churyumov-Gerasimenko in 2015, it detected chemicals strongly associated with biological life.
Very few scientists suggested that this could mean that organisms were actually living on the comet. According to the Panspermia theory, comets spread life to other planets as they go about their travels. More scientists dismiss the idea of comet-based life, but the presence of complex hydrocarbons on comets could be another sign that they were important in the appearance of life on Earth.
Meteorites look pretty when they streak into our atmosphere, but apart from making a wish on a shooting star, most people probably don’t pay them much attention. On the other hand, scientists have long looked at rocks that fell from space to uncover what they might reveal about the solar system. This includes looking for life in them.
While most meteorites originate from the asteroid belt and the leftover debris of the formation of the solar system, some come from other planets and moons. When a collision is big enough, rocks from the surface of a planet or moon can be ejected into space, where they wander until they fall to Earth. Several meteorites have been recovered that can be traced to Mars, and inside some of them are microscopic structures that some scientists interpret as fossils of Martian life.
In 1996, President Clinton announced the finding of such fossils in a Mars meteorite. The results of this discovery were soon questioned, but other researchers have come to similar conclusions about other Mars meteorites. Others have found the building blocks of proteins in meteorites. Next time you see a shooting star, maybe wish that it has indisputable proof of alien life inside it.
6 Gas Giants
In 1976 Carl Sagan and Edwin Salpeter published a paper examining whether Jupiter could be home to varieties of life. They concluded that Jupiter, whose atmosphere is mostly hydrogen and helium with methane, ammonia, and water, might actually be habitable for aliens. They would just be very alien aliens.
Jupiter does not seem a promising place for life at first, given it is far from the sun, has no solid surface, and has high wind speeds. Sagan and Salpeter came up with four types of organisms that might just call it home, however, and all live in the upper atmosphere. The first they call sinkers, which are small organisms that function like algae in Earth’s oceans. Floaters are vast animals kilometers across that move by taking in the gases of the atmosphere and expelling them as jets. They hold on to the hydrogen and helium, however, which helps them to float. They also posit species of hunters and scavengers in the Jovian atmosphere.
So far, nothing like this has been found, but other scientists have suggested that gas giants around other stars could be home to exotic life forms.
5 In Liquid Methane
Titan is the largest moon of the planet Saturn and the second largest in the solar system. It is surrounded by a thick atmosphere that gives the moon an orange and hazy look. It was only when probes reached Titan that its surface was uncovered. This revealed a world with a thick crust of ice, volcanoes that spray water and ammonia, and, most startlingly, lakes. Because the temperature of Titan is well below the freezing point of water, these lakes are not like ours on Earth but instead are made of liquid methane and ethane.
Could life have evolved to survive in these liquids instead of water? Models have been produced which would have organisms in these lakes metabolizing hydrogen and acetylene from the atmosphere to get their energy. These cells would have to be radically different from our own.
Earth cells have a phospholipid membrane around them, but these would break up in the hydrocarbon lakes of Titan. It’s just possible that cells of Titan could use acrylonitrile, a molecule found on Titan, to make membranes that would keep them together. Instead of our floppy membrane, these would be flat, hard, and crystalline.
What if the reason we are not detecting life is that all the aliens have gone to sleep? That is the suggestion of one team of researchers who have come up with what they call the “aestivation hypothesis.”
Why would alien civilizations decide to give up on being active and go into hibernation? According to the research, it is an efficient use of their efforts. We are currently living relatively early in the history of the universe. Only 14 billion years have passed since the Big Bang and galaxies are still relatively active with new stars being born all the time. But one day, the last star will die and there will be none to replace it. Energy will dissipate and the universe will be a colder and darker place. This might be just what the aliens are waiting for.
If they store a lot of energy now and go to sleep, they can wake up in the distant future and use their stores of energy to do more work with it due to the prevailing physical conditions of the universe. According to the research, the aliens who do this will get 10 times more work done if they are just willing to wait a bit… Say, several trillions of years.
3 Black Holes
A black hole is probably the last place you want to find yourself. If you slip below the event horizon, there is literally no way that you can escape its fearsome gravity. If a black hole is actively absorbing matter, then the entire region around it will be filled with high energy radiation that would kill most life. However, some researchers say that black holes might just offer sanctuary to organisms.
Black holes are not magical entities that just suck up everything around them. They pull in matter by gravity just like any other massive object. This means that if you are travelling at the right speed and in the right direction, you can orbit them like the earth orbits the sun. Planets could form from the matter surrounding a black hole.
Even the absence of the sun in a black hole planetary system might not be too much of a problem. The energy needed to support life could come from the searing hot accretion disc which forms around many black holes.
One of the reasons that we are not finding life in space is because we are looking at planets and not at space itself. Computer models produced by physicists in 2007 said that interstellar dust that is electrically charged could organize itself into something that behaves in a very life-like manner.
Atoms in space often exist as a plasma of charged ions, having had electrons stripped off by radiation. Unlike the familiar plasma of the sun, this plasma can be cold, which allows the ions to interact relatively non-violently. The simulations of such plasmas in low-gravity environments showed them forming into filaments that corkscrewed a little like DNA.
Once you have structures that can self-assemble, you can get evolution going. Different forms of filament were studied and were seen to evolve over time as they created more copies of themselves. Maybe aliens are out there; they were just more out there than we ever imagined.
Perhaps the most extreme form of alien life ever suggested by a serious researcher could be lurking within the inferno of active stars. If they exist, then they would not be made from ordinary matter or even objects that have been discovered.
Cosmic strings and magnetic monopoles would be needed for life to evolve within stars. Both of these are theoretical ideas in physics, but many scientists suspect that they might exist in the universe. Researchers have suggested that cosmic strings might be captured within the gravity of stars. Once inside the high temperature of a star’s interior, which is also filled with strong magnetic fields, the strings and monopoles would be twisted into complex forms. These shapes might be able to replicate themselves using other strings and monopoles. This is analogous to DNA copying itself.
The self-replicating strings could then evolve as they made copies of themselves with slight variations. Over time, the complexity of these stringy lifeforms could continue to grow into something very like life as we recognize it. Intriguingly, the authors of this research suggest that such lifeforms might be detectable as they influence the energy output of the stars they inhabit. So if the sun ever looks brighter than you expect, it might just be our neighbors saying hi.