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?

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 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

In Memory of Cassini

Last week, NASA’s Cassini Mission came to an end when the spacecraft crashed into the planet Saturn. This was, of course, a planned event: a way for the mission to end in a blaze of glory, collect a little extra data about Saturn’s atmosphere, and also protect Saturn’s potentially habitable moons (Titan, Enceladus, and possibly also Dione) from microorganisms that may have hitched a ride from Earth aboard the spacecraft.

Cassini’s last few days were an oddly emotional time, at least for me. Somehow knowing that the end was coming, that everything was proceeding according to schedule, made it a little harder to bear. When the words “data downlink ended” started appearing in my Twitter feed, I got a little misty eyes and had to walk away from the computer for a while.

This despite the fact that I never got to know Cassini all that well. I never really followed the Cassini Mission closely (especially compared the way I follow Juno). Looking back through my old posts, it seems Cassini only ever appeared on this blog twice. Once for that time it spotted sunlight glinting off the surface of Titan’s methane lakes…

… and once more for the time it used precise measurements of Enceladus’s librations to determine that Enceladus does indeed have an ocean of water beneath its crust.

So today I thought I’d turn the floor over to several of the moons of Saturn and also Saturn herself. They’re the ones who got to know Cassini well. Not me. It’s right that they get the chance to give Cassini’s eulogy.

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.

NASA’s Next Flagship Mission

Let’s imagine you’re NASA. You have two big flagship-class missions coming up: one to search for life on Mars (launcing in 2020) and another to search for life on Europa (launching in 2022). These flagship missions are big, expensive projects, so Congress only lets you do one or two per decade.

After 2022, the next flagship mission probably won’t launch until the late 2020’s or early 2030’s, but still… now is the time for you to start thinking about it. So after Mars and Europa, where do you want to go next? Here are a few ideas currently floating around:

  • Orbiting Enceladus: If you want to keep looking for life in the Solar System, Enceladus (a moon of Saturn) is a good pick. It’s got an ocean of liquid water beneath it surface, and thanks to the geysers in the southern hemisphere, Enceladus is rather conveniently spraying samples into space for your orbiter to collect.
  • Splash Down on Titan: If there’s life on Titan (another moon of Saturn), it’ll be very different from life we’re familiar with here on Earth. But the organic chemicals are there in abundance, and it would be interesting to splash down in one of Titan’s lakes of liquid methane. If we built a submersible probe, we could even go see if anything’s swimming around in the methane-y depths.
  • Another Mars Rover: Yes, we have multiple orbiters and rovers exploring Mars already, but some of that equipment is getting pretty old and will need to be replaced soon. If we’re serious about sending humans to Mars, it’s important to keep the current Mars program going so we know what we’re getting ourselves into.
  • Landing on Venus: Given the high temperature and pressure on Venus, this is a mission that won’t last long—a few days tops—but Venus is surprisingly similar to Earth in many ways. Comparing and contrasting the two planets taught us how important Earth’s ozone layer is and just what can happen if a global greenhouse effect get’s out of control. Who knows what else Venus might teach us about our home?
  • Orbiting Uranus: This was high on NASA’s list of priorities at the beginning of the 2010’s, and it’s expected to rank highly again in the 2020’s. We know next to nothing about Uranus or Neptune, the ice giants of our Solar System. Given how many ice giants we’ve discovered orbiting other stars, it would be nice if we could learn more about the ones in our backyard.
  • Orbiting Neptune: Uranus is significantly closer to Earth than Neptune, but there’s an upcoming planetary alignment in the 2030’s that could make Neptune a less expensive, more fuel-efficient choice. As an added bonus, we’d also get to visit Triton, a Pluto-like object that Neptune sort of kidnapped and made into a moon.

If it were up to me, I know which one of these missions I’d pick. But today we’re imagining that you are NASA. Realistically Congress will only agree to pay for one or two of these planetary science missions in the coming decade. So what would be your first and second choices?

Have I Been Drawing Enceladus Wrong?

Enceladus, one of Saturn’s moons, is becoming increasingly famous as one of those places in the Solar System where we’re most likely to find alien life. It certainly has the water for it. On this blog, I traditionally depict Enceladus like this:

It’s a nice, icy-looking world with a cheerful personality and active geysers in its south polar region. But have I been drawing Enceladus wrong this whole time? Would it make more sense to draw it like this?

Maybe. According to this article from Saturn Daily, Enceladus may have tipped sideways (by about 55°) at some point in its history. Apparently surface features reveal evidence of an old equator and old north and south poles.

The story is that one day, Enceladus was orbiting along, minding its own business, when it got whacked hard by an asteroid. Saturn Daily tells us that following the impact, Enceladus would have spent about a million years wobbling back and forth until it could reorient its rotation.

But Enceladus did manage to reorient itself. It has a new axis of rotation, a new north and south pole, and a new equator. It’s not a sideways moon, at least not anymore, which means by the logic of space cartoons, I’ve been drawing Enceladus correctly.

At least I think I have. What do you think? Does it make sense to draw Enceladus based on its current orientation or its (possible) original orientation?

Sciency Words: Libration (An A to Z Challenge Post)

Today’s post is a special A to Z Challenge edition of Sciency Words, an ongoing series here on Planet Pailly where we take a look at some interesting science or science related term so we can all expand our scientific vocabularies together. In today’s post, L is for:

LIBRATION

The Moon is tidally locked to the Earth, meaning one side is always facing toward us and the other side is always facing away. Except this tidal locking isn’t perfect. The Moon rocks back and forth just a little bit.

The technical term for this is libration. It comes from a Latin word meaning balance. In the visual simulation above (courtesy of Wikipedia), we can see the phases of the Moon on fast-forward. We can also see that the Moon moves a little closer to us and then a little farther away, due to its elliptical orbit.

And if you watch closely, you can see the Moon rocking or swaying back and forth. If you’re having trouble seeing it, I recommend picking a surface feature—a crater, perhaps—and following it with your eyes.

Of course our Moon isn’t the only moon that librates. I first learned about libration from a paper about Enceladus, a moon of Saturn.

Thanks to the Cassini mission, we were able to get extremely precise measurements of Enceladus’s libration, and we discovered Enceladus librates a lot. Like, a whole lot.

Enceladus librates so much that it cannot be solid all the way through. Instead, there must be a vast ocean of liquid water sloshing around inside, with only a thin, icy crust floating on top.

That’s a big deal because with all that liquid water, there’s a chance that maybe—just maybe—Enceladus could support life.

Next time on Sciency Words: A to Z, we’ll talk about metal. Everyone knows what metal is. Everyone except astronomers.

Sciency Words: Frost Line

Welcome to a very special holiday edition of Sciency Words! Today’s science or science-related term is:

FROST LINE

When a new star is forming, it’s typically surrounded by a swirling cloud of dust and gas called an accretion disk. Heat radiating from the baby star plus heat trapped in the disk itself vaporizes water and other volatile chemicals, which are then swept off into space by the solar wind.

But as you move farther away from the star, the temperature of the accretion disk tends to drop. Eventually, you reach a point where it’s cold enough for water to remain in its solid ice form. This is known as the frost line (or snow line, or ice line, or frost boundary).

Of course not all volatiles freeze or vaporize at the same temperature. When necessary, science writers will specify which frost line (or lines) they’re talking about. For example, a distinction might be made between the water frost line versus the nitrogen frost line versus the methane frost line, etc. But in general, if you see the term frost line by itself without any specifiers, I think you can safely assume it’s the water frost line.

Even though our Sun’s accretion disk is long gone, the frost line still loosely marks the boundary between the warmth of the inner Solar System and the coldness of the outer Solar System. The line is smack-dab in the middle of the asteroid belt, and it’s been observed that main belt asteroids tend to be rockier or icier depending on which side of the line they’re on.

It was easier for giant planets like Jupiter and Saturn to form beyond the frost line, since they had so much more solid matter to work with. And icy objects like Europa, Titan, and Pluto—places so cold that water is basically a kind of rock—only exist as they do because they formed beyond the frost line. This has led to the old saying:

dc23-outer-solar-system-christmas-party

Okay, maybe that’s not an old saying, but I really wanted this to be a holiday-themed post.

Meet a Moon: Dione

Regarding Greek mythology, it seems no one’s really sure who Dione was. Ancient sources contradict each other, and modern scholars think there may have actually been more than one mythical woman who went by that name. But I was able to find out this much: according to Wikipedia, at least one of these Diones was “sometimes associated with water or the sea.”

What that in mind, I’d like to introduce you to Dione, one of Saturn’s moons.

oc24-meet-dione

You sure are, Dione. In fact, I can’t think of a better description for you.

The Waters of Enceladus

Over the last decade or so, one of Saturn’s other moons has become famous for having an ocean of liquid water beneath its surface. That moon is called Enceladus. We know about Enceladus’s water for two reasons:

  • Geysers: Enceladus has a series of cracks (called tiger stripes) in its south polar region, and saltwater shoots out of these cracks at regular intervals.
  • Libration: Enceladus wobbles in place (librates) more than it should. This is best explained by the presence of a layer of liquid separating the moon’s crust from its core.

It’s still a mystery how Enceladus generates enough heat to keep its liquid water from freezing, but at this point, it’s pretty clear the water is there.

The Waters of Dione

Dione doesn’t librate the way Enceladus does, and we haven’t noticed any saltwater geysers, but a recent paper in Geophysical Research Letters says Dione might have a subsurface ocean too.

The authors of the paper created a new theoretical model for icy moons, a model which fits precisely with observations of Enceladus. Then they applied this new model to Dione and concluded that Dione should have a subsurface ocean.

This raises two questions that are fairly easily answered.

  • Where are Dione’s geysers?: Dione may not spew saltwater (anymore), but it does have cracks and fissures in its surface, suggesting that it may have had active “tiger stripe” geysers in the past.
  • What about Dione’s libration?: The new model suggests that Dione should librate, but not as much as Enceladus does. The Cassini spacecraft (currently orbiting Saturn) does not have instruments sensitive enough to detect the predicted libration.

So there you have it. According to at least one theoretical model, Dione should have a subsurface ocean, but we cannot yet confirm that it does. And it’ll probably be awhile before we can send a new spacecraft to Saturn to find out one way or another.

But hey, how appropriate is it that we named this moon, which might have a subsurface ocean, depending on your theoretical model, after a mythical figure that might sometimes have been associated with water, depending on which ancient sources your reading!