As the absurdity on our home planet grows, so does humanity's curiosity about life beyond 1 AU. Of course, wildly speculating about aliens is nothing new: It's been fuelling many facets of science fiction for years. But recently-proposed missions to "Ocean worlds" that could harbour microbial life make the search for extraterrestrials less tinfoil hat-like and a bit more tangible.
Illustration: Jim Cooke/Gizmodo
If we did find alien life, it would be the biggest discovery in human history. Most sci-fi tells us this will likely end poorly, but some of us choose to believe otherwise. If we keep an open mind and speculate wildly, some pretty interesting questions arise — most obviously, what the hell would aliens look like?
In this week's Giz Asks, we spoke to astrobiologists about what extraterrestrial life might look like if we ever find it. Hopefully it's more Arrival than Signs, but ultimately, I'm rooting for space capybaras.
Senior astronomer at the SETI (Search for Extra-Terrestrial Intelligence) Institute
What do you think is the most unrealistic depiction of aliens according to pop culture?
Well, I prefer the aliens that seem to be pretty intelligent. The Daleks were among that distinguished set, but their general resemblance to industrial-grade vacuum cleaners always inclined me to think that, as alien lifeforms go, they suck. And they were somehow considered to be mutants. Well, heck, we're ALL mutants, but at least we can climb stairs.
What's the closest thing on Earth we have to aliens?
Among earthly life forms, the most alien, to my mind, are insects. When you just see them flit across a room or picnic table, they're relatively unimpressive, even if annoying. But seen up close, they are truly alien — utilitarian and ingenious. Also ugly, although I suppose if you were, like Gregor Samsa, also an insect, you might find them appealing.
Astronomer, physicist, and PhD candidate in Space and Planetary Sciences at the University of Arkansas
What are some destinations outside our solar system where scientists think we might be able to find life?
If a planet is by a large enough star (for light) and is nestled within that star's Goldilocks zone — not too hot and not too cold for water — then that's a good start! However, as we are learning with Europa and Enceladus, it's entirely possible to have subsurface oceans that would be warm enough to house "life" and yet be very frozen on the outer surface.
Is it likely that life outside Earth would resemble anything we have here?
I'll put "life" in quotes due to it being a very vague term in regards to aliens. We have carbon-based life. But there's theories for sulphur-based and other chemistries to form some biological structures. "Life" could mean anything from microscopic blue cupcake-loving worms to sentient snorkels that like polka — not necessarily human-like. Not necessarily intelligent either.
President of METI International, which focuses on seeking out radio signals from intelligent extraterrestrial life
Obviously, we have yet to find life outside Earth. But if we did, what might it be similar to? Tardigrades? Whales?
Evolution relies heavily on chance events, so there's no reason to expect that the history of life as we've seen it on Earth would play out the same on other planets. And yet, we see cases on our own world in which similar environments seem to pull for creatures that are built the same. Sharks and dolphins have similar body forms, though they are far distant relatives, one being a fish and the other a mammal. We should not be surprised to see a similar convergence of body shape when we encounter life on other worlds. But the particular combination of details that define each species on Earth could result in a suite of creatures that vary radically from planet to planet. The bottom line is that we should not expect to see a duplicate of Homo sapiens as we look for life beyond Earth.
If we find life on the 'ocean worlds' within our own solar system, how might it present itself? How could it survive?
As we continue to explore our own solar system with robotic missions, we will be searching for signs of life indigenous to other planets and moons. Perhaps under the icy crust of Saturn's moon Enceladus we will someday find evidence of microbial life, living off the energy provided by hydrothermal vents. But the waters of Enceladus are so bone-chillingly cold that it would be hard to any imagine life there being much bigger than a bacterium.
Might we find life on another moon of Saturn? Titan is an intriguing possibility, with an atmosphere much denser than that of other moons, including carbon-containing molecules. The apparent lack of liquid water on its surface is a strike against Titan for habitability, but pools of liquid ethane and methane may provide a critical crucible for life. Given that Titan is much further from the Sun than is Earth, its surface temperature is also much lower.
Europa's potential habitability hinges on the fact that its subsurface ocean shows signs of liquid water in direct contact with the moon's mineral-rich mantle. Another factor in favour of Europa as an abode of life is that it seems to be generating energy from within, which could support the metabolic processes of life. Although some of this internal energy may arise from radioactive decay, even more energy is likely to come from tidal flexing. All of these are promising signs, but is it sufficient to yield something like a tardigrade on Europa? Let's be cautious, remembering that even on Earth, tardigrades are able to survive at the coldest temperatures and the greatest pressures for only a short time. As we seek out multicellular life on other worlds, it would need to be like a tardigrade on steroids, not only surviving a harsh environment for limited time, but being a true extremophile, thriving under conditions that are inconceivable for human beings.
Are the grey aliens from pop culture a pretty unlikely representation of what intelligent life would look like?
How likely are any intelligent beings on other worlds to look like the grey aliens from pop culture? Not very. To find a humanoid form on another world, a whole series of unexpected events would have to been replicated. Early hominids adapted to a particular niche on the savannas of Africa, their upright posture letting them see stronger, fiercer predators at a distance. Under a different environment, having a brain at the top of the body might be a liability, with increased risk of damage by falling but with no great advantage to compensate.
We see varied forms of intelligence on our own world. Octopuses are remarkably intelligent, but without controlling everything from a centralised brain. Instead, their "smarts" are largely distributed throughout their eight limbs. If we do make contact with intelligence on another planet, it means they have created radio or laser transmitters to signal us across the vast distances between the stars. But whether they did that with a pair of hands or a set of tentacles, we have no way of anticipating.
Astrobiologist at NASA
If we do find life outside Earth — let's say on a planet like Enceladus — how big or small would it (probably) be?
I doubt that it would more than a single cell life form so the size would be comparable to a bacterium. The environment of Enceladus does not lend itself to support multi-cellularity, in my opinion.
What do you think is the biggest misconception about finding life outside Earth?
That if a planet or moon is in the habitable zone around a star then it has what it takes for life. That is not true, especially if you go back to Jim Kasting's papers where he defines the habitable zone all it is is the zone where if water exists on a planet or moon that the water could be in a liquid state. That, however, is far from what it takes for life to originate and evolve.
You need all of the other ingredients for life and in the right form (e.g., reduced carbon, reduced nitrogen, phosphorus, etc.). Then once you have them they have to occur together in sufficient concentrations that they can chemically react.