Much has been said on this topic, but this post I saw recently reminded me how mistaken we might be in terms of the Drake Equation. In brief, the Drake Equation attempts to calculate how many intelligent, communicating civilizations there are in the galaxy, based on multiple parameters- the rate of star formation, the fraction of stars that have planets, the fraction of planets that will be habitable, the fraction of planets where life forms, the fraction of life that will achieve sentience, the fraction of sentient life that develops the ability to communicate, and their communicable window)
The ones that’ve been the biggest in the news recently have been the fraction of stars that have planets- the number keeps going up and up, as Kepler and other missions start to show that planets are EVERYWHERE- and the fraction that are habitable: we now know of two (GJ 667Cc and GJ 518d). Possibly. And they’re both within ~10 pc of the Sun, orbiting tiny M dwarfs.
But then there are the other things that have happened recently (at least as far as I know): As for “Fraction of planets that might be habitable”, the Solar System could be thought of for having FIVE such worlds: Earth (obviously), Mars (for the polar caps and permafrost layer), Titan (for its nice thick atmosphere and fairly earth-like methane cycle that mimics our water cycle), Europa (for its subsurface water) and Enceladus (for its subsurface water, again). So there’s a solar system with perhaps five worlds, most outside the traditional habitable zone anyway… It helps that we’ve found tons of extremophiles since Drake first conceived of his equation, including a microbe in a gold mine that is its own ecosystem and could presumably survive if we transplanted it directly to a similar location below the surface of Mars.
But then there’s that pesky “fraction that develop sentient life” thing. Once upon a time it meant humans, because we’re the only ones who use tools. Well, then there are the chimpanzees, the apes, seagulls using rocks to crack shells, and even ravens have been known to be spectacularly adept at tool use. If you go by the mirror test, Earth has MANY sapient life forms (“sentient” means intelligent, “sapient” means self-aware). There are the dolphins, and chimpanzees, and elephants (National Geographic has a particularly nice article about how elephants have excellent memories, social structures, and unfortunately also suffer post-traumatic stress disorder), as well as other primates, and magpies. There are even questions whether the mirror test is appropriate for dogs and cats, who do not rely on vision for all that much and perhaps should be given a pass for not noticing visual representations of themselves.
We’re now so certain of this that, as recounted in that first link, chimpanzee testing is being heavily restricted. It’s probably the first step toward actually giving all sapient beings appropriate rights. Assuming we don’t kill off all of them while destroying their habitats or poaching them specifically…
So: Life in the universe? If the Solar System can be taken as representative, not only are there multiple places in each solar system life could exist, but each world may hold several intelligent species.
Just don’t count on us talking to them. And maybe the fraction of sapient species that are communicative is a bit low; they just prefer swimming around in their own pool.