Abyssal Gigantism on Europa?

Hello, friends!

So the first time I heard about the subsurface ocean on Europa (one of Jupiter’s moons), my imagination ran wild.  Or should I say it swam wild?  I imagined all sorts of wonderful and terrifying sea creatures: krakens with lots of horrible tentacles and teeth; crab-like creatures scuttling around on the ocean floor; and perhaps even extraterrestrial merfolk with a rich and complex civilization of their own.

As I’ve learned more about space and science, though, I’ve scaled back my expectations for what we might find on Europa.  Or on Enceladus, or Dione, or Titan, or Ariel, or Pluto… there’s a growing list of planetoids in the outer Solar System where subsurface oceans of liquid water are suspected and/or confirmed to exist.

Any or all of those worlds might support alien life.  But not giant sea monsters.  When astrobiologists talk about alien life, they’re usually talking about microorganisms.  For Europa, rather than civilized merfolk and tentacle-flailing leviathans, we should imagine prokaryotic microbes clustered around hydrothermal vents, feeding on sulfur compounds and other mineral nutrients.  If we ever find evidence that these Europan microbes exists, it will come in the form of a weird amino acid residue, or something like that.

That’s the most exciting discovery we can hope for, realistically speaking.  Unless…

On Monday, I introduced you to the term “abyssal gigantism,” also known as “deep-sea gigantism.”  Abyssal gigantism refers to the tendency of deep-sea organisms to grow larger (sometimes much larger) than their shallow-water cousins.  As an example, see the giant squid.  Or if you really want to give yourself nightmares, look up the Japanese spider crab.

The more I read about abyssal gigantism, the more my thoughts turn to Europa (and Enceladus, and all the rest).  The environment beneath Europa’s icy crust shouldn’t be so different from the deepest parts of Earth’s oceans.  So shouldn’t what happens in the deepest parts of Earth’s oceans also happen on Europa?

According to this article from Hakai Magazine, yes.  Yes, it should.  The same evolutionary pressures that cause abyssal gigantism here on Earth should cause a similar kind of gigantism on Europa.  In fact, it would be strange if that didn’t happen.  One marine biologist is quoted in that article saying: “You would have to come up with a rationale why [abyssal gigantism on Europa] couldn’t happen, and I can’t do that.”

Before you or I let our imaginations swim wild, I should note that that article from Hakai Magazine was the one and only source I could find on this specific combination of topics: abyssal gigantism and life on Europa.  So maybe take all of this with a grain of salt (preferably a grain of Europan sea salt).  But… well, I’ll put it to you this way: if someone were to write a story about a NASA submarine being attacked by sea monsters, that story would seem plausible to me.

Sciency Words: Abyssal Gigantism

Hello, friends!  Welcome back to Sciency Words, a special series here on Planet Pailly where we talk about those weird and wacky terms scientists use.  This week’s Sciency Word is:

ABYSSAL GIGANTISM

In the deepest, darkest abyss of the ocean, animals have a tendency to grow to gigantic sizes.  This tendency is known as abyssal gigantism.  It’s also known as deep-sea gigantism.

Based on what Google Ngram Viewer has to show us, it looks like these terms (both abyssal and deep-sea gigantism) first appeared in the 1950’s, but people have obviously known that giant things live in the ocean for far longer than that.  Common examples of abyssal gigantism include the giant squid, the giant oarfish, and the Japanese spider crab.  All of these animals live in the deep, deep, deeeeeep ocean, and they all grow larger—considerably larger—than their shallow-water cousins.

What causes abyssal gigantism?  That’s not entirely clear.  As you might imagine, marine biologists have a tough time studying creatures that live that far down underwater.  But based on what I’ve read about this so far, the two most common explanations seem to be:

  • Keeping warm: Bigger animals can retain more of their own body heat.  That’s important if you live in extremely cold environments, like the deep oceans.  This is related to an ecological principle known as Bergmann’s rule.
  • Being metabolically efficient: Bigger animals tend to be more metabolically efficient, as modeled by something called Kleiber’s law.  In other words, big animals need less food relative to their size than smaller animals do.  That’s important if you live in an environment where food is scarce, like the deep oceans.

I have to admit I still have a lot to learn about this topic, and some of the things I read were a little confusing to me.  For example, I’ve read contradictory things about oxygen levels in the deep ocean and how that might factor into abyssal gigantism.

But that’s not the important thing.  You see, it’s not just that animals can grow to gigantic sizes in the deep ocean; it’s that they must.  For one reason or another, there’s evolutionary pressure on deep sea animals to get bigger and bigger and bigger.  And that’s got me thinking….

Next time on Planet Pailly, let’s revisit that very deep, very dark, very cold subsurface ocean on Europa.

Sciency Words: Stagnant Lid

Sciency Words: (proper noun) a special series here on Planet Pailly focusing on the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:

STAGNANT LID

Here on Earth, we have earthquakes.  Lots and lots of earthquakes.  And that’s very odd.

Maybe we should be thankful for all those earthquakes.  Our planet’s system of plate tectonics is unique in the Solar System.  Frequent earthquakes are a sign that Earth’s tectonic plates are still moving, that our planet is still geologically healthy.  The alternative would be stagnant lid tectonics, and that’s something we Earthlings probably don’t want.

In this 1996 paper, planetary scientists V.S. Solomatov and L.N. Moresi coined the term “stagnant lid” to describe what was happening on Venus—or rather what was not happening.  Venus doesn’t have active plate tectonics.  Maybe she did once, long ago.  If so, Venus’s plates somehow got stuck together, forming a rigid, inflexible shell.

The term stagnant lid has since been applied to almost every other planetary body in the Solar System, with the obvious exceptions of the four gas giants, and the possible exceptions of two of Jupiter’s moons: Europa and Ganymede.

According to this paper from Geoscience Frontiers, neither Europa nor Ganymede have truly Earth-like plate tectonics, but something similar may be happening.  The authors of that paper refer to the situation on Europa and Ganymede as “fragmented lid tectonics” or “ice floe tectonics.”  The upcoming Europa Clipper and JUICE missions should tell us more about how similar or different this is to Earth’s plate tectonics.

A stagnant lid does not necessarily mean that a planet or moon is geologically dead.  Venus and Io both have active volcanoes, for example, and it was recently confirmed that Mars has marsquakes.  But none of these stagnant lid worlds seem to be as lively as Earth—and I mean that in more ways than one.

If you buy into the Rare Earth Hypothesis, plate tectonics is one of those features that makes Earth so rare. Plate tectonics is something Earth has that other planets don’t, and thus it may be an important factor in why Earth can support life when so many other worlds can’t.

Meet Miranda, a Moon of Uranus

Miranda has been called the Frankenstein’s monster of the Solar System.  There’s just such a jumbled mismatch of landscapes.  You’d almost believe a mad scientist took pieces of several different moons and stitched them together.

Apparently this is a result of sporadic global resurfacing events.  At least that’s the conclusion of this 2014 paper entitled “Global Resurfacing of Uranus’s Moon Miranda by Convection.”  Due to a paywall, I haven’t been able to read that paper in full, but the research is summarized in articles here, here, and here.

Apparently Miranda used to have a more eccentric (non-circular) orbit than she does today.  Thus, the gravitational pull of Uranus would sometimes be stronger, sometimes weaker, causing Miranda to repeatedly compress and relax.  Imagine Uranus using Miranda like a stress ball and you’ll get a sense of what Miranda must’ve felt like.

All that squeezing and unsqueezing created friction and heat in Miranda’s interior.  Miranda’s internal ices got melty.  Convection cells formed underground, much like they do here on Earth, and some sort of tectonic and/or volcanic activity got started on the surface.

Something similar happens on Europa, a moon of Jupiter. As a result, Europa has the smoothest, youngest-looking surface in the whole Solar System.  So how did Europa turn out looking so beautifully smooth while Miranda turned into Frankenstein’s moon?

Based on what I’ve read, it sounds like Miranda’s orbit changed.  Uranus stopped squeezing Miranda like a stress ball, Miranda’s interior cooled off, and the resurfacing process came to a halt.  What we see today is a moon that is only half transformed by global resurfacing.

Personally, after studying reference photos of Miranda, learning about what happened to her, and drawing her portrait myself, I no longer feel comfortable with the whole Frankenstein’s monster thing.

I’d like to suggest a new metaphor: Miranda is the Picasso painting of the Solar System. Miranda does have a weird mishmash of surface features that don’t make a lot of sense together (much like a Picasso painting), but that doesn’t make Miranda monstrous.  It gives her her own strange, confusing beauty.

So yes, Miranda, to answer your question: I do think you’re beautiful.

Sciency Words A to Z: Young Surface

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, Y is for:

YOUNG SURFACE

Imagine a nice, smooth, clean sheet of asphalt: a parking lot, maybe, with no cracks or potholes or blemishes of any kind.  Just looking at it, you would know, with a reasonable degree of certainty, that this asphalt had been laid down recently. It’s new.  It is, in effect, a young surface.

In much the same way, planetary scientists can look at the surface of a planet or moon and infer, with a reasonable degree of certainty, how young or old that surface must be.  Look at the Moon or Mercury; they’re covered in craters, showing that their surfaces must be very, very old.  Or look at Mars, where some regions are more heavily cratered than others, implying (intriguingly) that some surfaces are relatively old and some are relatively young.

And then there’s Europa, one of Jupiter’s moons. Europa may be covered in weird, orangey-red cracks, and it may have a few other orangey-red blemishes, but overall it’s surprisingly smooth, and there are very few craters.  This makes Europa look a whole lot younger than it actually is.  In fact, Europa is said to have the youngest-looking surface in the whole Solar System.

Europa’s surface is made of ice, specifically water ice.  This is not so uncommon for a moon in the outer Solar System.  It’s so cold out there that water behaves like a kind of rock.

But unlike most other icy moons, Europa must be doing something to get rid of old, crater-y surface ice and replace it with new, clean, smooth ice.  And once you really start thinking of water as a kind of rock, you might be able to guess what Europa’s doing.  As stated in this paper from Nature Geoscience: “[…] Europa may be the only Solar System body other than Earth to exhibit a system of plate tectonics.”

Except unlike Earth’s techtonic plates, which float atop a layer of magma (liquid rock), Europa’s plates would be floating atop “magma” that is actually liquid water—twice as much liquid water as we have here on Earth, according to some calculations.

And while liquid water may or may not be necessary for life, we do have good reason to suspect that any place that has liquid water might also have life.  Personally, based on everything else I’ve learned about Europa, I’d be more surprised if we didn’t find something living there.

Next time on Sciency Words A to Z, I have a prediction for the future.

Sciency Words A to Z: JUICE

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, J is for:

JUICE

Speaking as a space enthusiast and a citizen of the United States, I have to confess I’m a bit disappointed with the status of the American space program.  While there have been some success stories—New Horizons, Curiosity, Scott Kelly’s year in space—I can’t help but feel like NASA has spent the last decade or so floundering.

However, it’s encouraging to see that so many other space agencies around the world are starting to pick up the slack.  My favorite example of this is the JUICE mission, a project of the European Space Agency (E.S.A.).

Astrobiologists have taken a keen interest in the icy moons of Jupiter.  There’s compelling evidence that one of those moons (Europa) has an ocean of liquid water beneath its surface.  There’s also a growing suspicion that two more of those moons (Ganymede and Callisto) may have subsurface oceans as well.

The original plan was for NASA and the E.S.A. to pool their resources for one big, giant mission to the Jupiter system.  But then the 2008 financial crisis hit.  The U.S. Congress was loath to spend money on anything—especially space stuff.  “Due to the unavailability of the proposed international partnerships […]”—that’s how this E.S.A. report describes the matter.

So the E.S.A. decided to go it alone. Personally, I think this was a very brave move.  E.S.A. has never done a mission to the outer Solar System before, not without NASA’s help.  But there has to be a first time for everything, right?  And so JUICE—the JUpiter ICy moons Explorer—began.  It’s not my favorite acronym, but it works.

According to E.S.A.’s website, JUICE will conduct multiple flybys of Europa and Callisto before settling into orbit around Ganymede.  You may be wondering why JUICE won’t be orbiting Europa.  This is in large part because of the radiation environment around Jupiter.  Europa may be more exciting to astrobiologists, but Ganymede is a safer place to park your spacecraft.

Meanwhile, NASA has recovered much of the funding it lost after the 2008 financial crisis, and they’re once again planning to send their own mission to the Jupiter system.  So maybe NASA and E.S.A. will get to explore those icy moons together after all!  Or maybe not.  According to this article from the Planetary Society, NASA’s budget is under threat once again.

I guess we’ll have to wait and see, but no matter what happens to NASA’s budget, E.S.A. seems fully committed to JUICE.  So speaking as a space enthusiast, at least I have that to look forward to.

Next time on Sciency Words A to Z, how do you measure the size of an alien civilization?

Sciency Words A to Z: Hydrothermal Vents

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, H is for:

HYDROTHERMAL VENTS

In his book All These Worlds Are Yours, Canadian astronomer Jon Willis recounts the story of how hydrothermal (hot water) vents were first discovered here on Earth.  It was 1977.  A scientific research vessel was towing a deep-sea probe along the ocean floor in the Pacific when the probe detected a temperature anomaly.

This was exactly what the crew of that research vessel was hoping to find: a sort of underwater volcano, right where two tectonic plates were moving apart.  But the real surprise came when that research team brought their deep-sea probe back to the surface and developed all its photographs.  They saw the hydrothermal vent they were expecting to see, but they also saw things living—yes, living!—all around it.

Marine microbiologist Holger Jannasch, who was part of a follow-up expedition in 1979, had this to say:

We were struck by the thought, and its fundamental implications, that here solar energy, which is so prevalent in running life on our planet, appears to be largely replaced by terrestrial energy—chemolithoautotrophic bacteria taking over the role of green plants.  This was a powerful new concept and, in my mind, one of the major biological discoveries of the 20th Century.

It’s become fashionable to suppose that, rather than the “warm little pond” that Charles Darwin once wrote about, perhaps life began its conquest of Earth in an environment like this: a place deep under water where heat and chemicals come spewing up out of the planet’s crust.

An Introduction to Astrobiology actually cites science fiction writer Arthur C. Clarke as the first to realize what all this might mean for life in our Solar System.  Specifically, Clarke thought of the icy moons of Jupiter.  In his 2001: A Space Odyssey novels, Clarke tells us of a hydrothermal vent on Europa—a “warm oasis” populated by plant-like, slug-like, and crab-like creatures.

The idea of life on Europa (or Saturn’s moon Enceladus) clustered around hydrothermal vents may have started out as science fiction, but it is now a possibility that astrobiologists take very seriously. But we’ll talk about that later this week.     

Next time on Sciency Words A to Z, what’s wrong with the I in SETI

Europa’s Cold Spot

I still have a ton of research reading to catch up on from 2018.  This weekend, I read a paper about Europa.  I wasn’t sure at first why this was on my to-be-read list, but by the end I knew why this one had caught my attention.

Europa is one of the icy moons of Jupiter.  It’s often listed as one of the most likely places in the Solar System where we might find alien life.  That’s because there’s evidence of a vast ocean of liquid water sloshing around beneath Europa’s icy crust.

Maybe someday we’ll be able to drop a little robo-submarine into that ocean and see if anything’s swimming around down there. But in the meantime, we’re really only able to explore Europa’s surface.  And as you can see in the highly technical diagram below, no matter where you go on Europa’s surface, it’s cold.  But in one specific region, Europa gets really cold.

Or at least, that one region appears to be extra cold.  This is a case where it’s important to understand how we get our data. We’re really measuring Europa’s thermal emissions, the amount of heat that gets radiated out into space. So that cold spot may represent one of two things:

  • Either that region absorbs less sunlight than the rest of Europa, and so it never heats up in the first place…
  • Or that region does a better job trapping the heat it absorbs from the sun, and so we detect less heat escaping back into space.

Either way, something weird is happening. Unfortunately, our previous missions to the Jupiter system did not provide us any useful photos of that one specific spot on Europa’s surface.  Our current Juptier mission, Juno, is unable to approach Europa at all, so that’s no help.

So we can’t match this anomalous cold spot to a visible surface feature.  However, the authors of the paper I read did suggest that this could be a sign of recent geological activity—the formation of chaos terrain, perhaps.

And if that’s true, we might (might!) find the waters of Europa’s subsurface ocean seeping up to the moon’s surface.  Maybe there’s fresh organic material seeping up onto the surface too.  Maybe.

Maybe.

Could be worth checking out, though.  Don’t you think?

My Favorite Moon: Io

Some of you may remember a post I did awhile back declaring Europa to be my favorite moon.  It’s a beautiful and mysterious world, a world that may have an incredible secret hidden beneath its icy crust.  Europa frequently tops the list of most likely places where we might find alien life.

But as I’ve learned more about the Solar System, I’ve developed a deeper affection for another moon, one of Europa’s neighbors, a world that is neither beautiful nor likely to support life.  I’m talking about Io.

Io is the innermost of Jupiter’s four big moons (Io, Europa, Ganymede, and Callisto).  As such, it gets pushed and pulled around pretty hard. Between Jupiter’s enormous gravity and the combined gravitational forces of the other three Galilean moons, it’s enough pushing and pulling to make anyone queasy.  And Io is a notoriously queasy planetoid.

Due to tidal forces, Io’s sulfur-rich interior is constantly boiling and churning.  And Io keeps literally spewing out its guts, making it the most volcanically active object in the whole Solar System.

Like Venus, my favorite planet, Io is a great chemistry professor, especially when it comes to sulfur chemistry.  Io’s also a pretty decent physics professor.  While most of the sulfur from Io’s volcanic eruptions settles back onto the moon’s surface, plenty of it escapes into space. The result: crazy dangerous games of particle physics in the vicinity of Jupiter.

Io’s ionized sulfur has a lot to do with controlling the intense radio emissions coming from Jupiter.  It’s also a major factor contributing to Jupiter’s insanely dangerous (to both humans and our technology) radiation environment. We recently learned that Jupiter has a third magnetic pole, located near the planet’s equator; while I haven’t read anything yet to back me up on this, I have a feeling Io is somehow responsible for that.

And lastly, Io’s ionized sulfur is partially (mainly?) responsible for the magnificent auroras that have been observed on Jupiter. And that’s my favorite bit about my favorite moon.  I love the idea that Io—the ugliest ugly duckling in the Solar System—plays such a crucial role in creating something beautiful.

But of course picking a favorite anything is a purely subjective thing.  Do you have a favorite moon?  If so, what is it?  Please share in the comments below!

The Titan Mission That Could’ve Been

This is a follow-up to my recent post about NASA’s next flagship-class mission. There seemed to be a lot of interest in the comments about a possible mission to Titan and/or Enceladus, Saturn’s most famous moons.

The competition for flagship mission funding can get pretty intense. The Titan Saturn System Mission (or T.S.S.M.) was a strong contender last time around, as was a proposed mission to Europa, the most watery moon of Jupiter.

According to Titan Unveiled by Ralph Lorenz and Jacqueline Mitton, things got a little nasty when the Europa team started calling Titan “Callisto with weather,” the implication being that Titan was geologically boring.

Callisto, by the way, is a large by often overlooked moon of Jupiter.

Ultimately Team Europa won. NASA deemed their proposal to be closer to launch-readiness. Now after a few years delay due to a certain global financial meltdown, the Europa Clipper Mission appears to be on track for a 2022 launch date (fingers crossed).

As excited as I am for Europa Clipper, the mission to Titan would’ve been really cool too. It actually would have included three—possibly four—spacecraft.

  • A lake-lander to explore Titan’s liquid methane lakes.
  • A hot air balloon to explore the organic chemical fog surrounding Titan.
  • A Titan orbiter to observe Titan from space and also relay data from the lander and balloon back to Earth.
  • And a possible Enceladus orbiter, built by the European Space Agency, which would have tagged along for the ride to Saturn.

It’s a shame T.S.S.M. didn’t get the green light from NASA. Just think: we would’ve had so many cool things going on at once in the Saturn System, enough to almost rival the activity we’ve got going on on Mars!

But now once Europa Clipper is safely on its way (again, fingers crossed), Team Titan will have another shot at getting their mission off the ground.