Floating predators. Googly-eyed monkeys. Sky cows. Brain matter in tanks. Sentient robots.
Netflix’s new series Alien Worlds covers them all. Each episode dreams up a fictional planet and the creatures who call it home. When you first see the fantastical critters and colorful plants on each world, you might dismiss the show as pure science fiction, but Alien Worlds is rooted in biology and evolution here on Earth.
What would happen to life on a planet where gravity was twice as strong? How would animals adapt to a planet around a dimmer star? Are we doomed to become a hive mind? Biologist and award-winning science fiction author, Philip Kramer, PhD, and Margaret Reeb, who works at the SETI Institute, have teamed up to break down the series.
Philip: The episode begins with the statement that “all living things need the same things, to feed, reproduce, and evolve.” This isn’t the exact definition of life, though, which is an entity that can grow, reproduce, undergo metabolic processes, and sense and interact with the environment. This simplistic definition has led to some interesting debates.
Margaret: Yes, it’s a very interesting question. One topical example is whether a virus is alive.
Philip: Crystals too can take in energy and materials from their environment and use it to grow and reproduce. Is a crystal alive? Alien life will also likely defy some of these rules. This flexibility is handy when you’re a scifi writer and want to come up with your own alien lifeform. Check out my post on the Science of Exobiology.
Margaret: I got very excited when they talked about extremophiles. Astrobiologists (the people who study the origins and natures of life) are very interested in these microbes because they can teach us a lot about different forms of life, including non-carbon organisms.
Philip: When they showed the Danakil Depression in Ethiopia, I thought for certain they were showing us some amazing CGI of an alien world at first. I had no idea this existed right here on Earth. A “Gateway to Hell,” or so they named it locally. The organisms here survive in acidic and near-boiling hot springs. Later in the episode, they give another example of bacteria that feed off hydrogen sulfide in dark caves. It makes you really appreciate just how varied Earth’s climates are and the lengths some organisms have gone to in order to survive the most extreme of them.
Margaret: So let’s talk about Janus, which orbits a red dwarf, or an M-type star. These are the smallest, coolest type of star, so a planet has to orbit very close in order to be warm enough to have liquid water. And, as the show points out, being this close to the star means the planet would be tidally-locked. So one side is always light and the other is always dark. The twilight zone in the middle is where most of the action happens.
Philip: It’s strange they don’t show crazy weather patterns on Janus. It can get up to 65C and as low as -50C on the day and night side of the planet. We know from Venus, which also has a slow rotation (its day is longer than its year), that the light and dark side of the planet are pretty similar in temperature due to the winds moving around the planet.
Margaret: True, that would have been interesting to see. Another thing to consider is planets orbiting red dwarf stars may end up without an atmosphere due to the UV radiation and solar flares they experience from being so close to their star. But from the show, it’s clear Janus has an atmosphere.
Philip: These spider-like creatures are the dominant life form on Janus, and depending on which side of the planet they grow up on, have extremely different characteristics. The day-side pentapods have a dark and shiny exterior to combat the extreme temperatures, while the night-side pentapods are covered in a thick fur.
Margaret: I thought the different types of pentapods were a little unbelievable at first. They seemed like over-the-top examples of polyphenism.
Philip: I admit, I thought the same, but they really made me a believer with their description of ant colonies. In order for a single ant species to be adaptable they need members of the colony to specialize, to switch their genes on and off selectively to become either workers, soldiers, and foragers.
Margaret: Okay, fine. I’ll get on board. I suppose. I still think it would be very hard for life to take root on the day-side of the planet. The Pentapods that lived on the dark-side of the planet were more believable to me.
Philip: They would have more access to water, that’s for sure, but they would also have to expend more energy just to keep from freezing to death. Using their comparison with scorpions, they need far less food to survive the heat.
Margaret: Scorpions! That was a great part of this episode. I had no idea those venomous little suckers could slow metabolism and go a whole year without eating anything.
Philip: As a scientist who studies metabolism, this was particularly interesting to me. Especially the insight into the energy sources of creatures that have no access to sunlight or starlight and the plants that grow beneath it. On Janus, the dark-side pentapods eat grubs around geothermal vents. Insects live off those microorganisms. We see the same principle around the volcanic vents on the bottom of the ocean.
Margaret: What did you think about the way the dark side pentapods ingested the bug’s biolumience?
Philip: I thought that was a clever adaptation. On Earth, the flamingo gets its characteristic pink color from Astaxanthin in the algae it ingests. But that is a pretty simple molecule. If the bioluminescence is anything like that found in fireflies, which requires a specific enzyme and substrate. I find it hard to believe the protein components would survive a digestive tract designed to break down organic matter. Which brings up the question, what do you make of their overall physiology?
Margaret: The overall look of these animals is very interesting and makes a lot of sense. The ability to move in any direction and see in all directions would be very important if food was scarce.
Philip: I somewhat disagree with that. Radial symmetry, where the layout of the creature is mirrored on more than one side, is very rare on Earth. Those creatures with radial symmetry are also pretty simple, like the starfish. Replicating so many complicated organs like eyes and appendages on all sides seems like a waste of resources. Scorpions and ants are bilateral, which seems much more efficient. Even the octopus is considered bilateral, and it still puts all of its arms to good use.
Margaret: What did you think about the way they reproduced?
Philip: Their being hermaphroditic means they both have the chance to produce offspring and increase their chances of survival as a species. While it is by no means uncommon on Earth, it is unusual for a creature this size to be hermaphroditic. The fact that it uses the same tooth-lined orifice for reproduction as eating is a bit terrifying. That it launches its offspring like tiny helicopters in the air is also pretty unique, though some species of spiders on Earth are known for something similar. They ride parachutes made of webs to disperse through the air soon after they hatch.
Margaret: I’m glad they discussed the importance of water, but I think it should have come in the first episode. Liquid water is the backbone of astrobiology so it seems like an important point to make early.
Philip: They did say that you need to “follow the water” in order to find life, but we also know that other solvents are being considered like ammonia and methane, and life itself might center around other elements like silicon or boron instead of carbon.
Margaret: “Follow the water” is an astrobiologist’s life motto! It’s interesting that you bring up methane. It makes me think of Titan, which is a moon of Saturn. It has methane lakes, which makes me wonder about what life could look like there.