Sciency Words: Europa Edition

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

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

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

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

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

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

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

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

Radiation on Europa: How Quickly Would It Kill You?

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

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

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

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

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

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

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

WANT TO LEARN MORE?

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

How Do They Know That: Europa’s Subsurface Ocean

Hello, friends!

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

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

HOW DO THEY KNOW THAT?
EUROPA’S SUBSURFACE OCEAN

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

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

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

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

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

WANT TO LEARN MORE?

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

October Is Europa Month Here on Planet Pailly!

Hello, friends!  Let’s talk about aliens!

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

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

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

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

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

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

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

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

WANT TO LEARN MORE?

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

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