The Common Europa Hypothesis

Hello, friends!  So Europa month ended a while ago, and I haven’t done much blogging since then.  Sorry about that.  I’ve been distracted by other writing projects.  But I now have some blog time in my schedule again, and I’m ready to blog about some new topics.  Except… I can’t help myself.  There’s one more thing I want to say about Europa.

I have this crazy idea.  I haven’t found much scientific literature to support me on this, but I still think this idea makes scientific sense.  I think that Europa—or rather, Europa-like worlds—may offer a solution to the Fermi Paradox.

For those of you who don’t know, in 1950, Italian physicist Enrico Fermi famously asked “Where is everybody?” in reference to extraterrestrial life.  Fermi argued that alien life should be all around us.  Almost everywhere we look in the cosmos, we should find alien beings waving back at us.  And yet, as of 1950, no real evidence of alien life had been found.  And as of today, in 2021, the situation remains much the same.

One possible answer to Fermi’s question came in the form of the rare Earth hypothesis.  Earth-like planets must be few and far between.  To be clear, when I say Earth-like planets in this context, I mean planets that meet the same Goldilocks parameters as Earth: not too hot, not too cold; not too big, not too small; not too wet, not too dry; et cetera, et cetera.  Planets that are so Goldilocks-perfect must be vanishingly rare in our universe.  Like, you could probably count on one hand how many Earth-like worlds exist in our whole galaxy.  So if life needs an Earth-like environment to survive, that may explain why alien life has been so frustratingly hard to find.

But then there’s Europa, the sixth moon of Jupiter.  Could there be life on Europa or on a Europa-like world?  And when I say a Europa-like world, I mean a world that looks like this:

A Europa-like world is a world with an ocean of liquid water covered up (and protected) by a thick shell of ice.  The mantle and core are hot, much like Earth’s, and hydrothermal vents on the ocean floor offer heat and nutrients to any potential life forms that might develop.

With respect to life on Europa herself, I’m 50/50.  There are good reasons to think Europa is habitable, and there are good reasons to think Europa falls just a little bit short of habitability.  But only a little bit.  Conditions on Europa are either just right for life or almost right.  So even if Europa misses the mark on habitability, another Europa-like world could easily hit it.

And here’s the important thing: while truly Earth-like worlds are rare, Europa-like worlds seem to be quite common.  There are at least two of them here in our own Solar System: Europa (obviously) and Enceladus, one of the moons of Saturn.  And there may be more.  In my research, Ganymede (moon of Jupiter), Dione (moon of Saturn), Titan (moon of Saturn), Ariel (moon of Uranus), and Triton (moon of Neptune) have all come up as places with certain suspiciously Europa-like qualities.  Even Pluto may have some liquid beneath her surface.

I’m choosing to call this idea the common Europa hypothesis, as a nod to the rare Earth hypothesis.  I think Europa-like worlds are common, both here in the Solar System and all across the cosmos.  Even if only 1% of these Europa-like worlds support life, that could still end up being an enormous amount of alien life out there.

Getting back to Enrico Fermi’s original question: “Where is everybody?”  Well, between the rare Earth and common Europa hypotheses, perhaps we have an answer.  Aside from us Earthlings and the lucky few who get to live on Earth-like planets, everybody is swimming around in Europa-like subsurface oceans, beneath thick layers of ice.

WANT TO LEARN MORE?

I suggest reading Exoplanets by Michael Summers and James Trefil.  Among other things, there’s plenty of discussion about all the surprising yet plausible places Europa-like worlds might exist.

Sciency Words A to Z: Rare Earth Hypothesis

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, R is for:

THE RARE EARTH HYPOTHESIS

Once upon a time, it was believed that the Sun, Moon, planets, and all the stars revolved around the Earth.  This was known as the geocentric theory.

Copernicus, Galileo, Kepler, and others set us straight about our planet’s physical location in space.  However, it is still sometimes asserted that Earth is special or unique in other ways.  Such assertions are often referred to in a derogatory sense as “geocentrisms.”

It’s tempting to dismiss the Rare Earth Hypothesis as just another geocentrism.  The idea was first presented in 2000 in a book called Rare Earth: Why Complex Life is Uncommon in the Universe by Peter Ward and Donald Brownlee.  In that book, Ward and Brownlee go through all the conditions they say were necessary for complex life to develop on this planet.  Crucially, they point out all the ways things could have gone wrong, all the ways complex life on Earth could have been prematurely snuffed out.

In other words, we are very, very, very lucky to be here, according to Ward and Brownlee, and the odds of finding another planet that was as lucky as Earth must be astronomically low.  Sure, there might be lots of planets where biology got started. Simple microorganisms may be quite common.  But complex, multicellular life like we have here on Earth—that’s rare.  And intelligent life forms like us are rarer still.  Perhaps intelligent life is so rare that we’re the only ones.

My favorite response to the Rare Earth Hypothesis comes from NASA astronomer Chris McKay.  In All These Worlds Are Yours, McKay’s argument is described as the Rare Titan Hypothsis.

Imagine intelligent life has developed on Titan (such a thing seems unlikely, I know, but there may be something living on Titan).  Titanian scientists look through their telescopes and soon realize that no other world in the Solar System is quite like their own.  Earth, for example, if too hot for life as the Titanians know it, and there’s far too much of that poisonous oxygen in the atmosphere anyway.  Furthermore, water would wreak havoc on what the Titanians would consider a biomolecule.

Perhaps a pair of Titanian scientists then decide to publish a book.  They list all the conditions required for complex life to develop on Titan, point out all the ways Titanian life could have been snuffed out prematurely, and argue that the odds of finding another Titan-like world must be astronomically low.

Personally, I think there’s some validity to the Rare Earth Hypothesis, but McKay’s point is worth bearing in mind.  There could be many different ways for life to develop in our universe.  Earth is but one example.  Planets that are just like Earth may indeed be rare—extremely rare—but there’s no reason to conclude that Earth-like life is the only kind of complex life out there.

Next time on Sciency Words A to Z… oh my gosh, we’ve finally made it to S!  It’s finally time to talk about SETI!