Sciency Words: Flora and Fauna

August 22, 2022August 22, 2022 ~ J.S. Pailly ~ 11 Comments

Hello, friends! Welcome to another episode of Sciency Words, a special series here on Planet Pailly where we talk about the definitions and etymologies of science or science related terms. In today’s post, we’re talking about two words:

FLORA AND FAUNA

So this weekend, I was thinking about alien life, as I often do, and it occurred to me that the words “plant” and “animal” are woefully inappropriate words to apply to extraterrestrial organisms. That got me wondering if maybe the words “flora” and “fauna” would be better.

This is hardly a revolutionary insight. Arik Kershenbaum talks about this in his book The Zoologist’s Guide to the Galaxy. You see, in the cosmic sense, when we’re considering life across the entire universe, the words “plant” and “animal” are highly Earth-specific terms. Strictly speaking, plants are organisms belonging to the kingdom Plantae, and animals are organisms belonging to the kingdom Animalia. These kingdoms are two branches of the tree of life—Earth’s tree of life. Not Mars’s tree of life. Not Proxima b’s tree of life. Earth’s.

Extraterrestrial life forms would belong to the kingdom… who the heck knows? I guess astro-taxonomists will have to figure that out if/when extraterrestrial life is discovered. In the meantime, would it make sense to use the words “flora” and “fauna” as generic terms for plant-like and animal-like aliens? Initially I thought it would, but after doing some research, I’m not so sure.

Definitions of flora and fauna: In ecology, the words flora and fauna refer to all the plants and animals, respectively, found within a particular ecological region.

Etymologies of flora and fauna: The word “flora” traces back to the Latin word for flower. Fauna comes from the name of an ancient Roman goddess of fertility.

So the words flora and fauna are not exactly synonyms for plants and animals; however, they do include the words “plants” and “animals” in their definitions. And extraterrestrials, no matter how plant-like or animal-like they may be, would still have to be categorized as something else.

I still feel like referring to alien life forms as flora and fauna is better than calling them plants and animals. Or at least it’s less wrong. But it’s still not perfect. In a distant, Sci-Fi future, new terminology may need to be invented.

WANT TO LEARN MORE?

I highly recommend reading The Zoologist’s Guide to the Galaxy by Arik Kershenbaum. Obviously we do not know at this point what alien life might be like, but, as Kershenbaum argues, we can make some educated guesses based on the way life on Earth does (or does not) work.

Sciency Words: Critical Zone

August 15, 2022August 15, 2022 ~ J.S. Pailly ~ 2 Comments

Hello, friends! Welcome to Sciency Words, a special series here on Planet Pailly where we take a closer look at the definitions and etymologies of science or science related terms, in order to expand our scientific vocabularies together. In today’s post, our Sciency Word is:

CRITICAL ZONE

So I could make this post about climate change, but I won’t. Certain people would just get angry with me in the comments, and I’m not in the mood for that today. So instead, I’m going to talk about Earth’s “critical zone” as something that could be relevant to astrobiological research.

Definition of Critical Zone: In Earth sciences, the critical zone is the surface and near surface environment of our planet—in other words, it’s the part of our planet where life lives. The proper scientific study of Earth’s critical zone will require an interdisciplinary approach, combining geology, biology, hydrology, and other related fields.

Etymology of Critical Zone: The term was first introduced in 1998 by American sedimentary geologist Gail Ashley. She called it the critical zone because, in her words, “it’s critical for life” and also because it is “critical to know more about it.” (Source: see the Eos article in the links below.)

Here’s a fun fact that I like to share at parties: there are somewhere between four and five thousand different minerals found here on Earth. Four to five thousand! Other planets in our Solar System are known to have only a few hundred, at best.

Why is Earth so mineralogically diverse? Plate tectonics, for one thing. Liquid water plays an important role as well. Some minerals can only form in the presence of liquid water. But the biggest factor, by far, is life. Living things do lots of weird chemistry, and all that weird chemistry messed with the planet’s soil and bedrock. Earth’s biosphere affects Earth’s geology. And Earth’s geology, in turn, affects Earth’s biosphere. There’s a synergistic relationship between living things and non-living rocks on this planet—and that is what the concept of Earth’s critical zone is all about.

I feel this is a terribly important concept to understand as it relates to Earth. It’s also something worth bearing in mind as we think about other worlds out there, worlds which may or may not support life of their own.

WANT TO LEARN MORE?

I’m going to recommend this article from Eos, entitled “Critical Zone Science Comes of Age.” I think that article is a pretty good summary of how critical zone research started and how it’s going, and it includes some quotes from Gail Ashley explaining what she was thinking about when she originally coined this term.

I’m also going to recommend this brief article entitled “‘Critical Zones’ on Mars and Across the Solar System,” which attempts to adapt the concept of the critical zone for other worlds.

And if you want to read more about why Earth is so mineralogically diverse, here’s a piece from EarthDate.org entitled “Minerals Evolve, Too.”

Our Place in Space: Xanadu

April 28, 2022April 26, 2022 ~ J.S. Pailly ~ 4 Comments

Hello, friends! Welcome to Our Place in Space: A to Z! For this year’s A to Z Challenge, I’ll be taking you on a partly imaginative and highly optimistic tour of humanity’s future in outer space. If you don’t know what the A to Z Challenge is, click here to learn more. In today’s post, X is for…

XANADU

`Titan is the largest moon of Saturn. It’s a very cold place. It’s so cold on Titan that water is basically a kind of rock, and certain chemicals that we typically think of as gases (i.e.: methane and ethane) flow freely as liquids. As a result, the surface of Titan looks surprisingly similar to some regions on Earth: a rocky landscape eroded by rain and rivers. Except the “rock” is frozen water, and the rain and rivers are a mix of liquified methane and ethane. One of the most curiously familiar “rock” formations on Titan lies near the equator. It’s called Xanadu.

Xanadu is an Australia-sized region of craggy hills and mountains. Due to Titan’s thick, hazy atmosphere, it’s impossible to see Xanadu (or any other surface feature on Titan) except in certain specific wavelengths, such as certain wavelengths of infrared. When Xanadu is visible, it appears as a bright splotch on Titan’s surface, surrounded by much darker desert terrain.

It’s unclear how Xanadu came to be. One hypothesis I read argues that Xanadu could be associated with some sort of giant impact event. Perhaps a large asteroid or comet smashed into Titan, disrupting the icy crust, which then refroze as this jagged and craggy terrain. Another hypothesis suggests that Xanadu was created by some sort of tectonic activity—a fascinating possibility. At this point, Earth is the only world confirmed to have plate tectonics.

In this Our Place in Space series, I’ve tried to emphasize all the cool and exciting things humans could do in the distant future. I have also mentioned, from time to time, my belief that humans in the distant future will learn to be good stewards of the Earth. Space exploration can help us do that. Titan is so curiously familiar, yet also so weirdly different from Earth. Trying to understand why Titan is so different-yet-similar can teach us much about our own world—which, in turn, will help us figure out how to take better care of our planet.

But there’s a catch. Just as we have a responsibility to take better care of Earth, we also have a moral responsibility to not mess up Titan. Remember Titan’s thick, hazy atmosphere? There are some weird chemicals forming in that atmosphere. Organic chemicals. Could those organic chemicals be associated, in one way or another, with biological activity? Maybe. Maybe not. No one can say at this point.

In the next few years, NASA will be sending a robotic helicopter to explore Titan’s Shangri-La region, one of the dark-colored regions directly adjacent to Xanadu. If we’re lucky, maybe that robo-helicopter will venture into Xanadu at some point. I have confidence that NASA will thoroughly sterilize all of their equipment before sending it to Titan to ensure that we do not contaminate Titan with our Earth germs.

There will be many more missions to Titan in the future. Just as Mars is crawling with Mars rovers today, Titan will be covered in Titan rovers, Titan helicopters, and Titan submarines in the future. The place has too much in common with Earth, and we simply cannot leave it unexplored. But humans in the distant future will not only be good stewards of the Earth; they’ll be good stewards of the Solar System. And so, whether we’re exploring Xanadu or Kraken Mare or Shangri-La, or any other region on Titan that has a super cool name, strict safety precautions will always be a must.

Want to Learn More?

I had a really hard time finding information about Xanadu for this post. I’m guessing that’s because very little information is available at this time. More exploring needs to be done! What I did find came from these three scientific papers:

Our Place in Space: The Wilderness

April 27, 2022April 26, 2022 ~ J.S. Pailly ~ 8 Comments

THE WILDERNESS

All month long, I’ve been telling you about how, in the distant future, human civilization will spread out far and wide across the Solar System. At the same time, I have rather casually been declaring various places in the Solar System should be off limits to humans. I feel perfectly justified in doing that after reading a certain research paper titled “How much of the Solar System should we leave as wilderness?”

I’m not going to summarize that paper in its entirety. If you want to learn more, you can check out the links in the “Want to Learn More?” section below. The main point I want to talk about, based on what that “wilderness” paper said, is that the Solar System is absolutely ginormous. You may think you understand how big the Solar System is. However big you think it is, it’s probably bigger than that.

As a result, we can declare insanely large swaths of territory and resources “protected wilderness” without inconveniencing ourselves. The paper advocates for establishing a one-eighth principle, meaning that our future space economy should be restricted to using only one-eighth of the resources in our Solar System. The remaining seven-eighths would be off limits. To quote from the paper:

We are required, as a point of social ethics, to accept reasonable constraints upon our self-interest in order to meet basic standards of justice between one another and (arguably) between ourselves and future generations. This is a precondition of having any sort of stable and lasting human society. However, we will take it that a livable ethic for society at large cannot ask for too much. More precisely, a reasonable social ethic cannot ask for anything so demanding that it is impossible, inconsistent with what we know about human psychology, or otherwise so demanding that it belongs only in the domain of private sacrificial commitment of a sort associated with political and religious ideals. The one-eighth restriction may seem to fall foul of this constraint.

Yes, the one-eighth principle sounds very demanding and restrictive at first glance. But, as the authors of that paper go on to explain, the Solar System is really big. Even if we make some highly optimistic assumptions about how fast the future space economy might grow, it would still take centuries to use up a full eighth of the Solar System.

This wilderness paper is now one of my all time favorite scientific research papers. It does make some important warnings for the future, though, and if you’re a fan of the kind of futurism I’ve been touting in this Our Place in Space series, I’d encourage you to check out the links below.

In the meantime, I declare that the rings of Saturn should be off limits to mining operations. Let’s preserve the natural beauty of those rings. Parts of Mars should be off limits as well—if we find alien life on Mars, perhaps the whole planet should be off limits. Same for many of the icy moons of Jupiter, Saturn, Uranus, and Neptune—especially Titan, Enceladus, and Ganymede—and most extra especially, Europa. Seriously, nobody mess with Europa!

Want to Learn More?

Click here to read “How much of the Solar System should we leave as wilderness?”

Or click here to read an article from Live Science summarizing the paper’s main points in less technical language.

Our Place in Space: Callisto

April 4, 2022April 3, 2022 ~ J.S. Pailly ~ 18 Comments

CALLISTO

The major moons of Jupiter are Io, Europa, Ganymede, and Callisto. In science fiction, Europa and Ganymede seem to get the most attention. Sci-Fi writers often end up putting human colonists (or at least a handful of plucky human scientists) on the surfaces of one or both of these icy moons. But today, I’m going to argue that Callisto would be a far more suitable home for future humans.

First off, and most importantly, there’s the issue of radiation. The space around Jupiter is one of the most dangerous radiation environments in the entire Solar System. As you can see in the highly technical diagram below, the radiation is most intense in the vicinity of Io. The radiation levels get better in the vicinity of Europa and continue to taper off when you reach Ganymede. You’re still soaking up a lot of radiation, though! Callisto’s radiation levels, however, are fairly low. You might even describe the radiation levels on Callisto as “survivable.”

Furthermore, planetary protection laws in the future may mean that both Europa and Ganymede are off limits to human settlers. Scientists today are 99.99% sure that Europa has a vast ocean of liquid water beneath her surface, and (as you know) wherever there’s water, there may also be life. There’s evidence suggesting Ganymede may have a subsurface ocean, too. Europa is often said to be the #1 most likely place where we might find alien life here in the Solar System. While the odds of finding life on Ganymede are considerably lower, the possibility of Ganymedean life shouldn’t be ignored.

There are already international agreements in place regarding extraterrestrial life. Space agencies like NASA, the E.S.A., and others are legally obligated to do everything they can to protect suspected alien biospheres from our Earth germs (and also to protect Earth’s biosphere from any germs we might find in outer space). For obvious reasons, these international agreements haven’t exactly been tested in court, and it’s a little unclear how they would be enforced.

But in a future where human civilization is spreading out across the Solar System, I’d imagine bio-contamination laws would become stronger, not weaker. Europa would almost certainly be declared off-limits to humans, unless it is proven beyond a shadow of a doubt that no aliens currently live there. Ganymede may end up being off-limits, too, for the same reason.

Meanwhile, we have Callisto. Scientists who want to study possible biospheres on Europa and Ganymede could set up a research station on Callisto. From there, they could keep a close eye on the other moons of Jupiter. They could operate remote-controlled probes to explore Europa and Ganymede without risking contamination, or they could go on brief excursions to Europa and Ganymede themselves (taking proper safety precautions, of course). While they’re at it, these scientist could also explore Io. Io is the most volcanically active object in the Solar System. There is virtually no chance that we’ll find life there, but studying Io’s volcanoes would still be interesting.

I’d be remiss if I didn’t mention this: Callisto might have liquid water beneath her surface, too. Not as much liquid water as Ganymede, and nowhere near as much as Europa, but still… it’s possible. Which means there’s a slim possibility that there could be life on Callisto. But in Callisto’s case, it is a very slim possibility. Based on what we currently know about Jupiter’s moons, Callisto still seems like the best place for humans to live. The radiation levels are much lower, the risk of bio-contamination is negligible… Yeah, if I were a science fiction writer, I’d put my human colonists on Callisto.

Want to Learn More?

In 2003, NASA published a plan to send astronauts to Callisto, with the intention of using Callisto as a base of operations to explore the other Jovian moons. Click here to read that plan. Some of the information is out of date, of course, but it’s still got some interesting ideas. Maybe someday, something like this plan could work!

I’d also recommend this article on Planetary Protection Policy, covering some of the rules that are already in place to protect planets and moons where we might find alien life.

P.S.: If I were a science fiction writer…? Wait a minute, I am a science fiction writer! Click here if you want to buy my first book. It’s not set on Callisto, unfortunately, but it’s still a fun story.

Arguing with Myself: The Search for Alien Life

February 23, 2022February 22, 2022 ~ J.S. Pailly ~ 24 Comments

Hello, friends!

So a certain argument has been playing out in the back of my mind for a long, long time now. Whenever I write, there are really two different versions of me who do my writing. On the one hand, there’s science enthusiast me. On the other, there’s Sci-Fi author me. And these two versions of me view science, space exploration, and the universe at large in dramatically different ways. One of the biggest ongoing disagreements I have with myself involves alien life.

Science enthusiast me believes that extraterrestrial microorganisms are pretty common in the universe. Science enthusiast me thinks we will find evidence of extraterrestrial microbes in the very near future, perhaps hiding under the ice on Mars or swimming around in the oceans of Europa, Enceladus, or even Titan. (I almost wrote unambiguous evidence there, but science enthusiast me also expects that confirming the discovery of extraterrestrial microbes will be tricky—just ask the researchers who found (or thought they found) microfossils inside a Martian meteorite back in 1996).

As for complex multicellular life—plants and animals, or whatever the extraterrestrial equivalent of plants and animals might be—science enthusiast me is far less optimistic. While microorganisms have proven again and again that they can survive almost anything, even direct exposure to the vacuum of space, multicellular organisms seem to be far more fragile, far less resilient. Earth may be one of the very few worlds where complex, multicellular organisms like us are able to survive and thrive over cosmic timescales.

And intelligent life? Science enthusiast me believes intelligent life must exist elsewhere in the universe—surely it must! But the universe is an awfully big place. Our nearest intelligent and communicative neighbors could be many galaxies away. Humanity is not alone in the universe, according to science enthusiast me, but we may as well be.

Sci-Fi author me, however, sees things from a different perspective.

Sci-Fi author me wants to write stories where encounters with alien life are commonplace, almost routine—stories where the aliens are sometimes friendly and sometimes not so friendly—stories where all sorts of weird and wacky interspecies adventures are possible! And Sci-Fi author me takes a particular and peculiar pleasure in handwaving away all the concerns and objections science enthusiast me might have, not just regarding alien life but also in relation to faster-than-light travel, time machines, cybernetics, et cetera, et cetera. Part of the fun, for Sci-Fi author me, is thinking up clever excuses for why impossible things are now possible (in the context of the story world, at least).

So there is this ongoing argument happening in the back of my mind. This argument is never going to end, and I’ve decided that that’s okay. Not every argument needs to have a winner and a loser, nor do arguments necessarily need to end in compromises. Sometimes a house divided can stand after all. Science enthusiast me believes the universe is like this; Sci-Fi author me would prefer (for story reasons) if the universe were more like that. And the tension between these two different versions of myself drives my creativity, both as a science blogger and a science fiction writer.

P.S.: For those of you who might be interested, both the “I Heart Science” and “I Heart Sci-Fi” designs in this post are available in my RedBubble store. Click here if you heart science, or click here if you heart Sci-Fi. And remember: nobody’s stopping you from clicking both if you heart both!

The Common Europa Hypothesis

November 17, 2021November 16, 2021 ~ J.S. Pailly ~ 19 Comments

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!

October 31, 2021October 30, 2021 ~ J.S. Pailly ~ 8 Comments

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.

“Planetary Protection in the New Space Era: Science and Governance” from Frontiers in Astronomy and Space Sciences.
“How Much of the Solar System Should We Leave as Wilderness” from Acta Astronautica.

Would Europa Life Have Bioluminescence?

October 26, 2021October 26, 2021 ~ J.S. Pailly ~ 16 Comments

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.

How Do They Know That: Europa’s Subsurface Ocean

October 4, 2021October 3, 2021 ~ J.S. Pailly ~ 6 Comments

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.