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.

Protect Europa!

Hello, friends!  We’ve reached the end of October, which means we’ve reached the end of Europa month here on Planet Pailly.  We still haven’t determined whether or not Europa is home to alien life, but I hope I’ve persuaded you to take the possibility of life on Europa seriously.

One question that came up a few times this month was whether or not we should send humans to Europa.  The answer, in my opinion, is no.  First off, as we discussed in a previous post, the radiation environment on Europa is crazy dangerous.  We humans would also struggle with the extreme cold and the very low surface gravity.  I’m not saying a colony on Europa is impossible, but there are far safer and easier places we could choose to go.  The neighboring moons of Ganymede and Callisto, for example, would serve as safer and more comfortable bases of operation for humans.

But there’s another reason why colonizing Europa seems like a bad idea to me.  It’s not a science reason.  It’s a legal issue.  There’s an international agreement in place (Article IX of the 1967 Outer Space Treaty) which forbids space agencies like NASA, the E.S.A., or Roscosmos from contaminating other worlds with our Earth germs.  The same agreement also forbids contaminating Earth with germs from other planets.

Some missions are considered riskier than others, contamination-wise.  For example, Article IX doesn’t really apply to NASA’s Parker Solar Probe.  There’s no chance Earth germs will be able to contaminate the Sun (and since the probe will not be returning to Earth, there’s no chance any lifeforms from the Sun could contaminate Earth).  There’s actually a whole risk categorization system in place, with five different categories of risk, and a bunch of sub-categories, too.  Click here if you want to know more details about that.

The important thing for our purposes is that any mission to Europa will involve a very high risk of contamination.  We may not know yet if alien life exists on Europa, but the possibility should be taken seriously.  The people who wrote the Outer Space Treaty made it clear that they’d learned the lessons of history and did not want to repeat the mistakes of the past.  We would not want Earth germs to endanger an alien ecosystem on Europa (nor would we want Europa germs endangering Earth-life).

So for the foreseeable future, I think Europa will be off limits to humans.  Europa might even be declared an interplanetary wilderness preserve, or something like that, and if there’s scientific research to be done on Europa, it can be done remotely from bases on Ganymede or Callisto.

There are easier places in the Solar System for us humans to colonize.  There’s no need for humans to go there.  So unless and until someone shows the contamination risk on Europa is zero, let’s leave Europa alone.

WANT TO LEARN MORE?

As part of my research for this post, I read the two papers listed below.  If you’re interested in how Earth laws work (or don’t work) in outer space, these papers are worth a look.  Also, if you’re interested in writing Sci-Fi, these papers may get the wheels of your Sci-Fi writer brain turning.

Would Europa Life Have Bioluminescence?

Hello, friends!

All month long, we’ve been talking about Europa, the sixth moon of Jupiter.  Scientists are 99% sure that there’s an ocean of liquid water beneath Europa’s icy crust, and speculation runs rampant about possible alien life swimming around in that subsurface ocean.

I’m currently reading a book called The Zoologist’s Guide to the Galaxy, by Arik Kershenbaum.  The book takes the fairly uncontroversial stance that the same evolutionary processes that shaped life on Earth would shape life on other worlds (uncontroversial among the scientific community, at least).  Specific details about biochemistry or genetics might be wildly different, but general principles like natural selection are likely universal.

Other science writers follow the same premise when imagining what we might find beneath the surface of Europa.  The environment is presumed to be very similar to the deepest, darkest reaches of Earth’s oceans.  Therefore, the same evolutionary pressures should apply, and Europa-life should have much in common with the deep ocean creatures we find here on Earth.

For example, Europa-life would probably cluster around hydrothermal vents, or similar geological hot spots, at the bottom of the ocean.  It’s nice and warm there, and there are plenty of tasty nutrients billowing up from the rocky mantle.

Another example: abyssal gigantism, which is the tendency for organisms in the deep ocean to grow to enormous sizes (compared to their shallow water cousins).  Scientists aren’t 100% sure why abyssal gigantism happens, but it may have something to do with metabolic efficiency.  If life in Earth’s deep oceans needs to be gigantic for the sake of metabolic efficiency, then Europa-life would probably be gigantic too.

A lot of science writers also predict that bioluminescence will be common on Europa.  It’s fairly common here on Earth, especially in the deepest, darkest regions of Earth’s oceans.  And as you can see in this totally legit photo from the Mariana Trench, bioluminescence is really pretty.

But while predictions about abyssal giants and hydrothermal vents make a certain logical sense to me, I’m not convinced bioluminescence makes sense on Europa.  As I understand it, life on Earth developed eyes first, and bioluminescence came later.

Having some sort of light-detecting organ makes sense on a world where there’s plentiful sunlight.  There’s an obvious evolutionary advantage to having eyes here on Earth.  And then, if some Earth-creatures decided to swim down to the bottom of the ocean, it makes sense for them to develop bioluminescence in order to help them see each other and the environment around them (or to help them lure in food).

But the ocean on Europa lies beneath a thick shell of ice.  There’s no sunlight there.  There has never been sunlight there.  So what is the evolutionary advantage of having eyes?  And if there’s no evolutionary advantage to having eyes, what would be the evolutionary advantage of bioluminescence?

Whenever Europa-life is depicted in science fiction, it’s almost always lit up in bold, bioluminescent colors.  A lot of science communicators seem to envision Europa-life that way too.  And why wouldn’t they?  To see all those strange alien creatures waving their glow-tentacles around—that would be an awe-inspiring sight!  But as awesome as it would be to see Europa-life in all its bioluminescent glory, I cannot think of a good reason why Europa-life would evolve that ability. Can you?

WANT TO LEARN MORE?

I haven’t finished reading The Zoologist’s Guide to the Galaxy yet, but what I’ve read so far is good, thought-provoking stuff.  If you’re interested in what alien life might really be like, scientifically speaking, then I’d say this book is worth a look.

The Colors of Europa: What’s That Red Stuff on Europa’s Surface?

Hello, friends!

Europa (one of the moons of Jupiter) is said to have the smoothest, youngest-looking surface of any planet or moon in the whole Solar System.  But Europa’s surface, as astonishingly smooth as it is, still isn’t perfectly smooth.  As you can see in the totally legit Hubble image below, there are dark-colored cracks and rough patches, and there are also blob-shaped discolorations that kind of look like the birthmark on Mikhail Gorbachev’s head.

I don’t want to get political on this blog, but this Gorbachev quote seems appropriate to me.

Fifteen to twenty years ago, when I started teaching myself about space, the things I read about Europa made it sound like scientists had no idea what caused the discolorations on Europa.  The blue-grey regions were frozen water, obviously; but the reddish-brown stuff… that could be anything!  Tholin?  Sulfur?  Amino acids?  Alien poo?  Anything.  Those reddish-brown areas may as well have been marked “here be dragons,” chemically speaking.

Today, though, it seems like scientists have seriously narrowed down the range of possibilities.

Sulfuric Acid: Io, one of Jupiter’s other moons, happens to be the most volcanically active object in the Solar System.  Io is so volcanically active that sulfur from Io shoots up into space and spreads to the neighboring Jovian moons.  On Europa, Io’s sulfur can react with Europa’s frozen water to create sulfuric acid (H2SO4).  This could explain some of the discoloration we see on Europa.

Epsom Salts: The discoloration could also be explained by a different sulfur compound: magnesium sulfate (MgSO4).  Also known as Epsom salts, magnesium sulfate is found in Earth’s oceans, and it’s reasonable to guess that it might be found in Europa’s subsurface ocean as well.  If so, magnesium sulfate could be spilling onto Europa’s surface through cracks and fissures in the surface ice.

Table Salt: In a previous post, I told you about the intense radiation environment on Europa’s surface.  Recent laboratory experiments have shown that sodium chloride (NaCl) can change color when exposed to that much radiation.  Just like magnesium sulfate, sodium chloride could be welling up to the surface through cracks and fissures in the ice.  And after a bit of radiation exposure, sodium chloride could cause the kind of discoloration we see on Europa.

So which of these three chemicals causes the discoloration on Europa?  Or is it some combination of all three?  From what I’ve read, I don’t think the scientific community has reached a consensus on that.  Much of the discoloration we see is in the vicinity of cracks, fissures, or other breaches in Europa’s surface.  That seems to favor sodium chloride and/or magnesium sulfate as the explanation.  However, one hemisphere of Europa is more exposed to the sulfur cloud coming from Io than the other.  And guess what!  The hemisphere that’s more exposed to Io is also more discolored!  That evidence seems to favor sulfuric acid as the explanation.

But again, I don’t think there’s a consensus about this yet.  This is still a topic of some debate among the scientific community.  However, the fact that we’ve gone from “it could be anything, here be dragons (chemically speaking)” to “it’s one or more of these three chemical substances” seems like real progress to me.

WANT TO LEARN MORE?

I relied on these three research papers for this post.  Together, I think they show the evolving conversation about Europa’s discolored regions over the last few years.

I wish I could recommend some easier and more accessible articles on this topic, but the ones I read all made claims like “scientists prove Europa’s covered in Epsom salts!”  Those sorts of articles do not reflect what the actual research papers are saying.

Sciency Words: Europa Edition

Hello, friends, and welcome back to Sciency Words!  That’s right, Sciency Words is back!  I’m going to handle this series a little differently than I did before.  I could explain what those differences are, but I think it’s better if we just dive right in so you can see for yourselves.

Since this is officially Europa Month here on Planet Pailly, we’re going to turn our attention to Europa, the sixth moon of Jupiter.  When exploring alien worlds, scientists sometimes discover geological features that are not found here on Earth.  When that happens, scientists need to invent new words to describe what they’re seeing.  Here are a few of the terms used to describe geological surface features seen on Europa.

Chaos Terrain: For the most part, Europa’s surface is made of very smooth, very fresh-looking ice.  But in some regions, we find these big, broken chunks of ice in a state of chaotic disarray.  Imagine a bunch of icebergs breaking loose from a glacier.  Now imagine that, before the icebergs drift too far, the water around them freezes, locking those icebergs in place.  That’s basically what chaos terrain looks like.  Oh, and chaos terrain tends to be discolored with some sort of reddish-brown substance.  Click here to see some chaos terrain on Europa.

Linea (plural, lineae): From the Latin word for line, linea means… line.  Reddish-brown lineae crisscross the surface of Europa.  They appear to be cracks in Europa’s icy surface, cracks which have been filled in by a mixture of freshly frozen ice and more of that reddish-brown substance.  Click here to see a color enhanced view of Europa’s lineae.

Lenticula (plural, lenticulae): From the Latin word for freckles, lenticulae are small, reddish-brown spots scattered all over the surface of Europa.  They tend to be round, but they don’t appear to be impact craters, which means they’re probably caused by something happening beneath Europa’s surface.  Click here to see a cluster of lenticulae on Europa’s surface.

Macula (plural, maculae): From the Latin word for spot, maculae are spots of discoloration on the surface of a planet or moon.  Europa’s maculae are irregularly shaped blotches of reddish-brown color.  At least one macula (known as Thera Macula) has been identified as a possible region of active chaos terrain formation.  Click here for a closer look at Thera Macula.

It’s extremely cold in the outer Solar System, so cold that water behaves almost like a kind of rock.  When thinking about icy worlds like Europa, it can be helpful to conceptualize water in that way.  Water is a kind of rock.  With that in mind, Europa’s icy surface is much like the rocky crust we have here on Earth, and Europa’s subsurface ocean of liquid water is sort of like the layer of molten rock that lies beneath Earth’s crust.  And thus the surface features we see on Europa might be caused by processes similar to the tectonic and volcanic activity we experience here on Earth.

There are, of course, other geological terms associated with Europa, but for this post I wanted to focus on just these four.  Europa’s chaos terrain, lineae, lenticulae, and maculae all have something important in common: that reddish-brown discoloration.  Next time on Planet Pailly, we’ll try to figure out what, exactly, that reddish-brown stuff on Europa is.

Radiation on Europa: How Quickly Would It Kill You?

Hello, friends!  If you happen to have any radiation protection clothing lying around—like those lead aprons they give you for X-rays at the dentist—I recommend putting it on now before you read any further.  In today’s post, we’ll be exploring the radiation environment of Europa.

Europa is often listed as one of the top four places in the Solar System where we might find alien life.  That makes exploring Europa a top priority for NASA and other space agencies.  Unfortunately, Europa is one of the moons of Jupiter, with an orbit that puts Europa deep inside Jupiter’s radiation belts.

Radiation is going to be a problem wherever you go in space, but the radiation belts around Jupiter are extra scary. If you were to spend a few days on the surface of the Moon or Mars without any sort of radiation protection gear, you’d end up with a significantly higher risk of developing cancer at some point later in life.  If you spent a similar amount of time on the surface of Europa without radiation protection, you wouldn’t live long enough to worry about cancer.  Radiation sickness would kill you in a matter of days—maybe a matter of weeks, if you’re “lucky.”

– NASA’s Juno space probe flying through radiation near Jupiter.

Even robotic spacecraft have a tough time dealing with Jupiter’s radiation belts.  The Juno mission, currently orbiting Jupiter, has all its mission critical electronics sealed up inside what NASA calls a radiation vault.  It’s basically a big, heavy box with thick walls made of titanium.  The radiation vault cannot block all of the radiation, but it blocks enough of it that Juno should survive long enough to finish its mission.

NASA’s upcoming Europa Clipper mission, which will take an even closer look at Europa, will be equipped with a similar radiation vault.

Before we end today’s post, some of you may be wondering what all this radiation means for potential alien organisms living on Europa.  Well, it probably wouldn’t affect them much, if at all.  The aliens (if they exist) would be swimming around in Europa’s subsurface ocean, beneath several kilometers worth of water ice.  And large quantities of water happen to be one of the very best radiation shields nature can provide.

WANT TO LEARN MORE?

  • “Colonization of Europa” from Wikipedia.  Yeah, it’s a Wikipedia article, but if you’re interested in what it would take to put human beings on the surface of Europa, this article is a pretty good place to start.
  • “Juno Armored Up to Go to Jupiter” from nasa.gov.  This is a press release from 2010, when the Juno spacecraft was still under construction.  It describes, in plain English, what Juno’s radiation vault is and why Juno needs it so badly.
  • “Spent Fuel Pool” from What If?  For those of you who didn’t know about water’s incredible radiation blocking powers, this is an amusing look at water’s incredible radiation blocking powers.

How Do They Know That: Europa’s Subsurface Ocean

Hello, friends!

This month is Europa month here on Planet Pailly!  For those of you who haven’t met Europa before, she’s one of the moons of Jupiter, and she’s generally counted among the top four places in the Solar System where we might find alien life.  This is in large part because Europa has a vast, global ocean of liquid water hidden beneath her surface.  By most estimates, Europa has twice as much liquid water as Earth!

But one might reasonably ask how we know, for certain, that Europa’s ocean of liquid water exists.  I mean, no space probe has ever cracked through Europa’s surface to check.  Not yet, anyway.  Which brings us to another episode of “How Do That Know That?”

HOW DO THEY KNOW THAT?
EUROPA’S SUBSURFACE OCEAN

There are three main lines of evidence pointing to the existence of Europa’s ocean: spectroscopic evidence, gravitational evidence, and magnetic evidence.

  • Spectroscopy: Every chemical substance in the universe interacts with light in its own unique way.  Very specific wavelengths of light will be absorbed and/or emitted, depending on what chemical substance you’re looking at.  So by measuring the wavelengths of light reflecting off Europa, scientists could determine what Europa’s surface is made of.  I won’t leave you in suspense.  The answer is water.  Frozen water.
  • Gravity: In the 1990’s, NASA’s Galileo spacecraft conducted several close flybys of Europa.  Each time, Europa’s gravity nudged Galileo ever so slightly off course.  By measuring exactly how much gravitational nudging Galileo experienced, scientists could calculate what Europa’s internal structure must be like.  Turned out there was a thick layer of low density material near the surface.  Water, in either a frozen or liquid phase, has a pretty low density.
  • Magnetism: Jupiter has an absurdly powerful magnetic field.  As Europa orbits Jupiter, a mysterious something inside Europa responds to Jupiter’s magnetism, creating what’s called an “induced magnetic field” around Europa.  Once again using data from the Galileo spacecraft, scientists could measure the shifting and changing intensity and orientation of Europa’s magnetic field as she orbited Jupiter.  As it so happens, a large volume of saltwater would react to Jupiter’s magnetic field in much the same way as the mysterious something inside Europa.

Taken individually, each line of evidence would have to be considered inconclusive.  Suggestive, perhaps, but ultimately inconclusive.  Sure, spectroscopy tells us there’s frozen water on Europa’s surface, but that layer of frozen water might only be skin deep.  Gravity data tells us there’s a very deep layer of low density material, but gravity data, by itself, cannot tells us what that low density material is.  And if you didn’t know anything else about Europa’s internal structure or chemical composition, then her induced magnetic field could be explained in many different ways.  Taken together, though, these three lines of evidence leave little room for doubt: there’s an ocean of liquid water (specifically saltwater) beneath the surface of Europa.

Science is, in my mind, a little like trying to solve a crossword puzzle.  Not all the answers are obvious at first, but with each word in the puzzle you find, the intersecting words become a little easier to figure out.  Maybe you thought the answer to 17 across (What’s beneath the surface of Europa?) could be three or four different things.  But then you found out the middle letter is a T, and the last letter is an R, and now you can narrow down the possibilities to one and only one solution.

By following multiple lines of evidence, scientists can now say, with a very high degree of certainty, that there’s an ocean of liquid water beneath the surface Europa.  Exactly how thick is the ice above that ocean?  And what minerals are present in the ocean?  How much hydrothermal activity occurs at the bottom of that ocean?  Those are some of the next questions that need answers.

WANT TO LEARN MORE?

There’s a lot of information out there about Europa.  A little too much, actually.  It’s hard to sort through it all.  So if you want to learn more about Europa, I highly recommend Alien Oceans: The Search for Life in the Depths of Space by Kevin Peter Hand.  It’s got all the best Europa facts you could ever want, all together in a single book.  And Hand devotes a full chapter to each of those lines of evidence that I listed above.

October Is Europa Month Here on Planet Pailly!

Hello, friends!  Let’s talk about aliens!

If we want to find alien life, where should we look?  Well, if money were no object, I’d say we should look anywhere and everywhere we can.  Phosphorous on Venus?  Could be aliens.  Let’s check it out.  Melty zones beneath the surface of Pluto?  Let’s check that out too.  Ariel?  Dione?  Ceres?  Let’s check them all for signs of alien life!

But money is an object.  We simply don’t have the resources to explore all of these places.  Space exploration is expensive.  Space exploration will always be expensive so long as we’re stuck using rocket-based propulsion.  The Tsiolkovsky rocket equation makes it so.

Whenever you’re working within a restrictive budget, you need to think strategically.  With that in mind, astrobiologists (scientists who specialize in the search for alien organisms) have focused their efforts on four worlds within our Solar System.  Their names are Mars, Europa (moon of Jupiter), Enceladus (moon of Saturn), and Titan (another moon of Saturn).

This month, I’m going to take you on a deep dive (no pun intended) into Europa.  In my opinion, of the four worlds I just listed, Europa is the #1 most likely place for alien life to be found.  I don’t mean to denigrate Mars, Enceladus, or Titan.  There are good reasons to think we might find life in those places, too.  But there are also good reasons to think we might not.

  • Mars: Life may have existed on Mars once, long ago.  But then the Martian oceans dried up.  We’re unlikely to find anything there now except, perhaps, fossils.
  • Enceladus: Enceladus’s age is disputed.  She may be only a few hundred million years old, in which case she may be too young to have developed life.
  • Titan: If you want to believe in life on Titan, you have to get a little imaginative about how Titanian biochemistry would work.

Europa doesn’t have those issues.  Unlike Mars, Europa has an ocean of liquid water right now, in modern times.  Unlike Enceladus, Europa’s age is not disputed; she’s definitely old enough for life.  And unlike Titan, Europa doesn’t require us to get imaginative about biochemistry.  The same carbon-based/water-based biochemistry we use here on Earth would work just as well for the Europans.

There are still good reasons to search for aliens on Mars, Enceladus, and Titan.  Finding fossils on Mars would be super exciting!  Enceladus’s age is, as I said, in dispute, with some estimates suggesting she’s very young, but others telling us she’s plenty old.  And while life on Titan would be very different than life on Earth, scientists don’t have to imagine too hard to find plausible ways for Titanian biochemistry to work.

But if I were a gambler, I’d put my money on Europa.  And if I were in charge of NASA’s budget, I’d invest heavily in Europa research and Europa missions.  Europa just seems like the safest bet to me, if we want to find alien life. And in the coming month, I plan to go into more detail about why I feel that way.

WANT TO LEARN MORE?

If you’re interested in learning more about the Tsiolkovsky Rocket Equation, you may enjoy this article from NASA called “The Tyranny of the Rocket Equation” (because NASA is the American space agency, and anything Americans don’t like is tyranny).

As for astrobiology, I highly recommend All These Worlds Are Yours: The Scientific Search for Alien Life, by Jon Willis.  Willis frames the search for alien life just as I did in this post: alien life could be anywhere, but you only have a limited budget to use to find it.  So how would you spend that money?