Tag: Astrobiology

How Do They Know That: Europa’s Subsurface Ocean

~ 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.

October Is Europa Month Here on Planet Pailly!

~ J.S. Pailly ~ 6 Comments

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?

Sciency Words: Morphospecies

~ J.S. Pailly ~ 6 Comments

Hello, friends!  Welcome back to Sciency Words, a special series here on Planet Pailly where we talk about those weird and wonderful words scientists like to use.  In this week’s episode of Sciency Words, we’re talking about:

MORPHOSPECIES

The clearest definition I’ve found for “morphospecies” comes from Wiktionary.  According to Wiktionary, a morphospecies is: “A species distinguished from others only by its morphology.”  In other words, do these two animals look alike?  If so, then they’re the same morphospecies.  This is in contrast to taxonomic or phylogenic species, which take other factors into account, like evolutionary history or reproductive compatibility.

Classifying organisms by their physical appearance alone will lead to obvious problems.  Think of caterpillars and butterflies, as an example.  Or think of all the plants and animals that have evolved to mimic other plants and animals.  As this paper from the Journal of Insect Science warns, the morphospecies concept should only be used in circumstances “where morphospecies have been assessed as reliable surrogates for taxonomic species beforehand.”

However, in some cases physical appearance may be the only thing we know about an organism or group of organisms.  I’ve been reading a lot about xenophyophores lately.   They’re my new favorite unicellular organisms (more about them later this week).   Xenophyophores live in the deepest, darkest reaches of the ocean, and marine biologists have had a very difficult time studying them.  Given how little we know about xenophyophores, classifying them by physical appearance alone may be (in some cases, at least) the best we can do.

As a science fiction writer, I wonder how useful the morphospecies concept would be for studying and categorizing life forms on some newly discovered alien world.  It would be problematic, for sure, and I’d want to read more about this topic before sticking the word “morphospecies” into a story.  But my gut feeling is that classifying alien organisms by morphospecies might be the best we could do, at least at first.

Abyssal Gigantism on Europa?

~ J.S. Pailly ~ 11 Comments

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.

Venus Has Phosphine Fever

~ J.S. Pailly ~ 15 Comments

Hello, friends!

Over the last decade or so, Mars has been trying really hard to convince us that he can (and does) support life.  We’ve seen evidence of liquid water on the Martian surface, and traces of methane have been detected in the Martian atmosphere.  These things are highly suggestive, but none of that proves Martian life exists.

It would be nice if we knew of a chemical that clearly and unambiguously proved that a planet has life, wouldn’t it?  According to this paper published in Nature Astronomy, phosphine (chemical formula PH3) might be the clear and unambiguous biosignature we need.  Here on Earth, phosphine gas is a waste product produced by certain species of anaerobic bacteria.  It’s also produced by humans in our factories.  Either way, the presence of phosphine in Earth’s atmosphere is strong evidence that there’s life on Earth.

And according to that same paper from Nature Astronomy, astronomers have now detected phosphine on another planet.  No, it wasn’t Mars.

Okay, we humans do know of non-biological ways to make phosphine, but they’d require Venus to be a very, very different planet than she currently is.  For example, Venus would need to have a hydrogen-rich atmosphere, or Venus would have to be bombarded constantly with phosphorus-rich asteroids, or the Venusian surface would have to be covered with active volcanoes (more specifically, Venus would need at least 200 times more volcanic activity than Earth).

None of that appears to be true for Venus, so we’re left with two possibilities:

  • There is life on Venus.
  • There’s something we humans don’t know about phosphine, in which case phosphine is not the clear and unambiguous biosignature we hoped it was.

In either event, Venus is about to teach us something.  Maybe it’s a biology lesson.  That would be awesome!  Or maybe it’s a chemistry lesson.  Personally, I’m expecting it to be a chemistry lesson.  There must be some other way to make phosphine that we humans never thought of.

P.S.: Now I’m sure a lot of you are thinking: “Wait a minute, don’t Jupiter and Saturn have phosphine in their atmospheres too?”  You’re right.  They do, and we’ll talk about that in Wednesday’s post.

Sciency Words: Aerobiology

~ J.S. Pailly ~ 2 Comments

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we talk about those weird and wonderful words scientists like to use.  Today on Sciency Words, we’re talking about:

AEROBIOLOGY

You will find life pretty much anywhere you go on Earth.  Living things are in the water, on the land, and up in the air.

Aerobiology comes from three Greek words meaning “air,” “life,” and “the study of.”  So aerobiology is the study of airborne life, specifically airborne microbial life.  According to the Oxford English Dictionary, the term was first introduced in the late 1930’s.

I have to confess I am totally new to aerobiology.  I only found out about this term yesterday, and I don’t want anything I say to misrepresent the field.  But based on what I have read, it sounds like aerobiologists are primarily concerned with protecting public health from the spread of pollen and other allergens, as well as the spread of airborne diseases.

However, aerobiologists also study airborne microbes that are not a direct threat to human health—and this is the part that connects to the outer space stuff I normally write about.  For decades now, aerobiologists have known that algae and other common microorganisms can fly up into Earth’s atmosphere and travel great distances on the wind.  And according to this 2001 paper, microorganisms can (and do) remain active—growing and reproducing—inside the water droplets found in clouds.  As the authors of that 2001 paper explain it, we should start thinking of clouds as microbial habitats.

So what does this have to do with outer space?  Well, if clouds on Earth can serve as a habitat for microorganisms, then maybe microorganisms could exist in the clouds of some other planet.

And by some other planet, I mean Venus.

And by maybe, I mean stay tuned for Monday’s post.

A Breath of Fresh Hydrogen

~ J.S. Pailly ~ 10 Comments

Hello, friends!

So let’s imagine that extraterrestrials don’t breathe oxygen.  Oxygen is a pretty dangerous chemical, after all, so there’s good reason why alien organisms might want to avoid it.  But what would these aliens breathe instead?

A few years back, I came across an interesting “fact” on a conspiracy theory website.  The government doesn’t want you to know this, but apparently a lot of alien species breathe hydrogen.  That conspiracy theory website said a lot of weird and wacky things, but this hydrogen-breathing alien idea… based on what I know about chemistry, that idea kind of made sense to me.

You see we Earthlings use oxygen to oxidize our food.  This oxidation reaction generates the energy we need to stay alive.  But oxidation reactions are sort of equal-and-opposite to reduction reactions.  Oxygen is a powerful oxidizing agent, obviously, but hydrogen?  Hydrogen is a pretty effective reducing agent.

A paper published earlier this year examined the possibility of Earth-like planets with hydrogen-rich atmospheres.  Such planets could, in theory, exist, but they’d have to meet one or more of the following criteria:

  • The planet would have to be much colder than Earth (think Titan or Pluto-like temperatures).
  • The planet would have to have much higher surface gravity than Earth.
  • The planet would have to continuously outgas hydrogen from some underground source (subsurface reservoirs of water ice mixed with methane ice might do the trick).

If one or more of these conditions are not met, then a hydrogen-rich atmosphere would quickly fizzle out into space through a process called Jeans escape.

Now, could life exist in that sort of hydrogen-rich environment?  The answer is yes.  Absolutely yes.  Even here on Earth, there are organisms that “breathe” hydrogen and use it to generate energy through reduction reactions.  These organisms can be found deep underground, or clustered around deep-sea hydrothermal vents, or in other exotic niche environments where hydrogen is plentiful and oxygen is rare.

The real question is: could hydrogen-breathers evolve into complex, multicellular life forms?  Earth’s hydrogen-breathers are mere microorganisms.  Their version of respiration is nowhere near as efficient as the oxygen-based system we humans and our animal friends use.  The inefficiency of hydrogen-based respiration has stunted the evolutionary development of Earthly hydrogen-breathers.

But maybe on another planet—a planet with a hydrogen-rich atmosphere unlike anything Earth has ever seen—maybe complex multicellular life could evolve on a planet like that.  Maybe.

It’s plausible enough for science fiction, at least.

How Proxima b Lost Its Ozone Layer

~ J.S. Pailly ~ 6 Comments

Hello, friends!

Today we’re visiting Proxima Centauri, one of three stars in the Alpha Centauri system, the star system right next door to our own.  And it turns out Proxima has at least one planet.  Not only that: Proxima’s planet is orbiting within the habitable zone.  That planet may have liquid water on its surface, and perhaps even life!

Proxima’s planet, known officially as Proxima b, orbits about 0.05 AU away from its star.  That puts Proxima b closer to its star than Mercury is to our Sun.  But that’s okay.  Proxima Centauri is much smaller, dimmer, and colder than our own Sun, so everything balances out.

But I have bad news.  The temperature might be right for life, but the radiation environment is all wrong.  Proxima Centauri is a very angry little star.  It’s much angrier than our Sun.  Solar flares, solar wind, and solar radiation are a whole lot worse than anything Earth would normally have to worry about.

In March of 2016, Earth-based astronomers observed a “superflare” on Proxima Centauri.  As you can see in the highly technical diagram below, that superflare would have done serious damage to Proxima b’s ozone layer (assuming Proxima b had an ozone layer in the first place).

According to this 2018 paper on ozone loss, if superflares like that are normal for Proxima Centauri, we should expect Proxima b to lose 90% of its ozone layer in just five years (again, assuming Proxima b had an ozone layer in the first place).  Without an ozone layer, incoming ultraviolet radiation would thoroughly sterilize Proxima b’s surface (much like it does on Mars).

And it gets worse.  Earth’s magnetic field deflects a lot of harmful solar and cosmic radiation away.  But according to this 2016 paper on space weather, Proxima b’s magnetic field (assuming Proxima b has a magnetic field) is taking a real beating.  The magnetic field would be badly weakened and compressed.  As a result, Proxima b’s atmosphere would start eroding away, due to the solar wind, and if those UV rays haven’t already killed everything on the surface, all that solar and cosmic radiation would have a chance to finish the job.

Even the most extreme of extremophiles here on Earth would have a tough time surviving on Proxima b.  But the situation is not hopeless.  That 2016 paper on space weather and that 2018 paper on ozone loss both acknowledge that there are still plausible scenarios where life could evolve and thrive on Proxima b.  But in order to do it, the Proxima b-ians must have done one of two things:

  • Life on Proxima b must be very specifically adapted to that radiation environment, or…
  • Life on Proxima b must have found a good hiding place, perhaps deep underwater or underground, where the radiation can’t reach it.

Next time on Planet Pailly, it’s a bird!  It’s a plane!  It’s… oh no, it’s a killer asteroid!!!

Something Worth Knowing

~ J.S. Pailly ~ 9 Comments

Hello, friends!

Today I’d like to share a very old video I found on YouTube.  It’s a series of man (and woman) on the street interviews where people are asked if they think we’ll find life on other planets.

According to the video description, this was filmed in 1962.  It’s interesting to me to hear people talk about the possibility of finding “vegetable” and/or “animal” life on Venus.  At that time, the Soviet Union’s Venera 1 spacecraft would have already visited Venus; however, due to a technical glitch, Venera 1 failed to transmit any data about Venus back to Earth.  So surface conditions on Venus were still unknown to us Earthlings.

But setting aside the Venus stuff in particular, in general people’s opinions about space exploration and extraterrestrial life have not changed much since 1962.  Some people are enthusiastically optimistic, others think it’s all nonsense, and a lot of people don’t seem to care one way or the other.

Then, of course, you get the one guy who swears he’s seen a U.F.O.  And then, of course, you get the guy who’s “working off the theory of the Bible,” where it says God only created life on one planet (F.Y.I., I’ve read the Bible too, and I don’t remember it ever saying that).  So again, not much has changed since 1962.

But my favorite is the woman at 1:40 who says she doesn’t expect we’ll find any life on Venus, but then goes on to say we’ll still find “something worth knowing.”  I’d say she was right on both counts!

Personally, I do think there’s life on other planets, and also on other moons (I’m looking at you, Europa).  But regardless of whether or not we find alien life out there, we should absolutely keep searching and keep exploring.  I suspect we will continue to learn all sorts of things that are worth knowing!

Next time on Planet Pailly, we’ll learn how to dance like binary stars.

Sciency Words: The Silurian Hypothesis

~ J.S. Pailly ~ 9 Comments

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:

THE SILURIAN HYPOTHESIS

I’ve heard several variations on this joke.  Why did the dinosaurs go extinct?  Because they didn’t put enough money into their space program.

But what if that isn’t a joke?  What if the dinosaurs (or some other prehistoric creatures) did establish an advanced civilization right here on Earth millions of years before we came along?  Could such a civilization come and go without leaving any trace for us modern humans to find?  Or could the traces be there for us to see, and we just haven’t recognized them yet?

In 2018, NASA astrobiologists Gavin Schmidt and Adam Frank presented this idea in a formal scientific paper titled “The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?”  As Schmidt and Frank explain in a footnote:

We name the hypothesis after a 1970 episode of the British science fiction TV series Doctor Who where a long buried race of intelligent reptiles “Silurians” are awakened by an experimental nuclear reactor.  We are not however suggesting that intelligent reptiles actually existed in the Silurian age, nor that experimental nuclear physics is liable to wake them from hibernation.

Schmidt and Frank go on to examine some of the ways human industrial activities have changed this planet, and how those changes are being recorded geologically.  They also examine a few of the oddities and anomalies in the geological record as we currently know it.

To be clear, there is absolutely no definitive evidence that another advanced civilization existed on Earth before our own.  Schmidt and Frank go to great pains to emphasize that they don’t actually believe their own hypothesis to be true.

The Silurian Hypothesis is intended to be more of a thought experiment than anything else.  It’s meant to help us better understand how human civilization is changing this planet, and also (remember Schmidt and Frank are NASA astrobiologists) how alien civilizations might be changing their own worlds.

P.S.: The Silurian Hypothesis is also a wonderful example of how science fiction can inspire real life science.