The Colors of Europa: What’s That Red Stuff on Europa’s Surface?

Hello, friends!

Europa (one of the moons of Jupiter) is said to have the smoothest, youngest-looking surface of any planet or moon in the whole Solar System.  But Europa’s surface, as astonishingly smooth as it is, still isn’t perfectly smooth.  As you can see in the totally legit Hubble image below, there are dark-colored cracks and rough patches, and there are also blob-shaped discolorations that kind of look like the birthmark on Mikhail Gorbachev’s head.

I don’t want to get political on this blog, but this Gorbachev quote seems appropriate to me.

Fifteen to twenty years ago, when I started teaching myself about space, the things I read about Europa made it sound like scientists had no idea what caused the discolorations on Europa.  The blue-grey regions were frozen water, obviously; but the reddish-brown stuff… that could be anything!  Tholin?  Sulfur?  Amino acids?  Alien poo?  Anything.  Those reddish-brown areas may as well have been marked “here be dragons,” chemically speaking.

Today, though, it seems like scientists have seriously narrowed down the range of possibilities.

Sulfuric Acid: Io, one of Jupiter’s other moons, happens to be the most volcanically active object in the Solar System.  Io is so volcanically active that sulfur from Io shoots up into space and spreads to the neighboring Jovian moons.  On Europa, Io’s sulfur can react with Europa’s frozen water to create sulfuric acid (H2SO4).  This could explain some of the discoloration we see on Europa.

Epsom Salts: The discoloration could also be explained by a different sulfur compound: magnesium sulfate (MgSO4).  Also known as Epsom salts, magnesium sulfate is found in Earth’s oceans, and it’s reasonable to guess that it might be found in Europa’s subsurface ocean as well.  If so, magnesium sulfate could be spilling onto Europa’s surface through cracks and fissures in the surface ice.

Table Salt: In a previous post, I told you about the intense radiation environment on Europa’s surface.  Recent laboratory experiments have shown that sodium chloride (NaCl) can change color when exposed to that much radiation.  Just like magnesium sulfate, sodium chloride could be welling up to the surface through cracks and fissures in the ice.  And after a bit of radiation exposure, sodium chloride could cause the kind of discoloration we see on Europa.

So which of these three chemicals causes the discoloration on Europa?  Or is it some combination of all three?  From what I’ve read, I don’t think the scientific community has reached a consensus on that.  Much of the discoloration we see is in the vicinity of cracks, fissures, or other breaches in Europa’s surface.  That seems to favor sodium chloride and/or magnesium sulfate as the explanation.  However, one hemisphere of Europa is more exposed to the sulfur cloud coming from Io than the other.  And guess what!  The hemisphere that’s more exposed to Io is also more discolored!  That evidence seems to favor sulfuric acid as the explanation.

But again, I don’t think there’s a consensus about this yet.  This is still a topic of some debate among the scientific community.  However, the fact that we’ve gone from “it could be anything, here be dragons (chemically speaking)” to “it’s one or more of these three chemical substances” seems like real progress to me.

WANT TO LEARN MORE?

I relied on these three research papers for this post.  Together, I think they show the evolving conversation about Europa’s discolored regions over the last few years.

I wish I could recommend some easier and more accessible articles on this topic, but the ones I read all made claims like “scientists prove Europa’s covered in Epsom salts!”  Those sorts of articles do not reflect what the actual research papers are saying.

Oops! I Learned Something Wrong About Io

Hello, friends!

As you may remember from a previous post, Io is my favorite moon in the Solar System.  He may not be the prettiest moon, and he certainly isn’t the most habitable.  I, for one, would never, ever, ever want to live there.  You see, Io is the most volcanically active object in the Solar System.  He is constantly—and I do mean constantly!—spewing up this mixture of molten hot sulfur compounds.  It gets everywhere, and it is totally gross.

But it’s also super fascinating—fascinating enough that Io ended up becoming my #1 favorite moon in the whole Solar System.  I’ve read a lot about Io over the years.  I thought I understood Io pretty well.  But I was wrong.  One of the facts in my personal collection of Io-related facts was based on a fundamental misunderstanding of how Io’s volcanism works.  Let me explain:

Io is caught in this gravitational tug of war between his planet (Jupiter) and his fellow Galilean moons (Europa, Ganymede, and Callisto).  Jupiter’s gravity pulls one way; the moons pull another; Io is caught in the middle, feeling understandably queasy.  I always thought this gravitational tug-of-war was directly responsible for Io’s volcanic activity.  But it’s not.  Recently, while reading a book called Alien Oceans: The Search for Life in the Depths of Space, I realized that I had some unlearning to do.

The gravitational tug-of-war has forced Io into a highly elliptical (non-circular) orbit.  This means there are times when Io gets very close to Jupiter, and times when Io is much farther away.  When Io’s orbit brings him close to Jupiter, Jupiter’s gravity compresses Io’s crust.  And when Io moves father away, his crust gets a chance to relax.  This cycle of compressing and relaxing—of squeezing and unsqueezing—causes Io’s interior to get hot, which, in turn, keeps Io’s volcanoes erupting.

This squeezing and unsqueezing action wouldn’t happen if not for Io’s highly elliptical orbit, so the gravitational tug-of-war with Jupiter’s other moons is still partially responsible for Io’s volcanism.  But the tug-of-war is not the direct cause of Io’s volcanism, as I always assumed it to be.

I wanted to share all this with you today because some of you may have had the same misunderstanding about Io that I did.  Hopefully I’ve cleared that up for you!  But also, I think this is a good example of how the process of lifelong learning works.  If you’re a lifelong learner (as I am), you may have favorite topics that you think you know an awful lot about.  But there’s always more to learn, and sometimes learning more means unlearning a few things that you thought you already knew.

WANT TO LEARN MORE?

If you’re an Io fanatic like me, I highly recommend Alien Oceans: The Search for Life in the Depths of Space by Kevin Peter Hand.  The book is mainly about Europa and the other icy/watery moons of the outer Solar System, but there’s a surprising amount of information in there about Io, too.  Apparently, if it turns out that Europa really is home to alien life (as many suspect her to be), then Io may have played a crucial role in making that alien life possible.

Sciency Words: Plasma Torus

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:

PLASMA TORUS

Astronomers have discovered thousands of planets out there.  Exoplanet hunting techniques have gotten so good that astronmers are now moving on to the next great challenge: finding exomoons.  And one possible method for detecting exomoons involves something called a plasma torus.

Ever since the 1960’s, we’ve known something weird was happening with Io, one of the moons of Jupiter.  In 1964, an astronomer by the name of E.K. Bigg determined that Io had some strange power over Jupiter’s magnetosphere.  Subsequent research identified clouds of ionized sulfur and sodium in the vicinity of Io’s orbit.  Then in 1979, NASA’s Voyager 1 space probe photographed Io up close, catching Io in the act of spewing a mix of sulfur compounds and other noxious chemicals into space.

We now know that Io is the most volcanically active object in the Solar System and that Io’s volcanic activity directly affects Jupiter’s magnetic field.  As you can see in this totally legit Hubble image, Io has created a nasty mess around Jupiter.

All those nasty chemicals get swept up in Jupiter’s powerful magnetic field, which acts like a supersized particle accelerator, turning those chemicals into a high-energy plasma.

I can’t be sure who coined the term plasma torus, but a multitude of papers from the 1960’s and 70’s (like this one, or this one, or this one) attempt to model the plasma clouds surrounding Jupiter as a torus—torus being the fancy mathematical term for “donut-shape.”

The nifty thing about Io’s plasma torus is that you can detect it even from a great distance.  Even if you’re too far away to observe Io directly, you can still infer that she’s there based on all those ionized chemicals swirling around Jupiter and the effect those chemicals have on Jupiter’s magnetic field.

So could we find volcanically active exomoons by looking for plasma tori?  According to this paper from The Astrophysical Journal, we sure can—and maybe we already have!  The paper identifies the signatures of possible plasma tori encircling several large exoplanets.

One thing I’m not sure about: when we find a plasma torus, can we be 100% certain it’s caused by an exomoon?  Are there any other natural (or unnatural) phenomena that might cause a plasma torus to form?  I don’t know.

P.S.: Safety warning to any space adventurers who might be reading this.  A plasma torus is a high radiation environment.  Keep your distance!

Sciency Words: Stagnant Lid

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

STAGNANT LID

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

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

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

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

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

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

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

My Favorite Moon: Io

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

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

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

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

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

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

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

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

Io: Jupiter’s Ugliest Moon

For today’s post, I hopped in my imaginary spaceship and flew all the way out to Io, one of Jupiter’s moons. Without a doubt, Io is the ugliest object in the Solar System.

I know, that’s mean. I shouldn’t say things like that. But come on, just look at it. Seriously, look at it. It’s like some moldy horror you might find in the back of the fridge.

So yeah, Io’s hideous. Let’s go look at something else instead. Something pretty, like Jupiter’s auroras.

We have auroras back on Earth, of course, but Jupiter’s are a whole lot bigger, a whole lot more powerful, and when viewed in ultraviolet, a whole lot brighter. Also, unlike Earth’s auroral lights which come and go, Jupiter’s are always there. They may vary in intensity, but they never stop, never go away.

Auroras are caused by charged particles getting caught in a planet’s magnetic field, directed toward the magnetic poles, and colliding at high speed with molecules in the planet’s atmosphere.

On Earth, those charged particles come mostly from the Sun in the form of solar wind. No doubt the solar wind contributes to Jupiter’s auroras as well, but the greater contributing factor is actually—believe it or not—Io. That’s right: ugly, little Io causes Jupiter’s auroras. I guess spreading ionized sulfur all over the place is good for something after all!

In fact if you ever get to see a Jovian aurora, you’ll notice little knots in the dancing ribbons of light. These knots correspond to the positions of several of Jupiter’s moons. And the largest, brightest, most impressive of these knots… that one belongs to Io.

Jupiter.Aurora.HST.mod.svg
Image courtesy of Wikipedia.

So I guess today’s lesson is that even the ugliest object in the Solar System can still help make the universe a more beautiful place.

Sciency Words: Plasma Torus

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

PLASMA TORUS

Saturn may have the most beautiful rings in the Solar System, but Jupiter’s got the most impressive plasma torus. Torus is the proper mathematical term for a donut shape, and plasma refers to ionized gas. Put the two words together and you get a giant, donut-shaped radiation death zone wrapped around a planet’s equator.

Jupiter’s plasma torus is faint, almost invisible; but if we take the totally legit Hubble image below and enhance the sulfur emission spectra, you’ll see what we’re talking about.

Ever since the discovery of Jupiter’s decametric radio emissions, astronomers have known there must be a relationship between Jupiter’s magnetic field and its moons. Well, I say moons plural, but it’s really only one moon we’re talking about: Io.

It wasn’t until the Voyager mission that we figured out why Io has so much influence over Jupiter’s magnetic field. In 1979, the Voyager space probes discovered active sulfur volcanoes on Io. They also detected ionized sulfur and oxygen swirling through space conspicuously near Io’s orbital path.

It seems that due to Io’s low surface gravity, Io’s volcanoes can easily spew a noxious mix of sulfur dioxide and other sulfur compounds up into space. Jupiter’s intense and rapidly rotating magnetic field acts as a sort of naturally occurring cyclotron, bombarding these sulfur compounds with radiation, breaking them apart into ionized (electrically charged) particles and accelerating those particles round and round the planet.

The result is a giant, spinning, donut-shaped cloud of ionized gas. We’re talking about a lot of radiation here—seriously, keep your distance from the Io plasma torus! We’re also talking about a lot of electrically charged, magnetically accelerated particles moving through a planetary magnetic field.

One source I read for today’s post described Io as “the insignificant-looking tail that wags the biggest dog in the neighborhood.” Jupiter has by far the largest, strongest magnetic field of any planet in the Solar System, but thanks to this plasma torus, it’s Io—tiny, little Io—that has the real power in the Jovian system.

Next week, we’ll go take a look at Jupiter’s auroras. They’re rather different from the auroras we have here on Earth, and SPOILER ALERT: Io has a lot of control over them.

Sciency Words: Decametric Radio Emissions

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

DECAMETRIC RADIO EMISSIONS

The decameter doesn’t get as much love as the meter or the kilometer, but it’s still a perfectly legitimate S.I. unit of measure. It equals ten meters.

In 1955, astronomers Bernard Burke and Kenneth Franklin detected radio emissions coming from the planet Jupiter, radio emissions with wavelengths long enough to be measured in decameters. Thus these emissions came to be known as the decametric radio emissions.

Surprisingly, the decametric radio emissions don’t radiate out into space in all directions. Instead, they shoot out like laser beams. Or perhaps I should compare them to searchlights. As a result, we can only detect them here on Earth if they happen to be aimed right at us.

Now here’s the part that I find really interesting. There are currently seven known sources for the decametric radio emissions, and they’re classified into two groups: Io-dependent and Io-independent.

The Io-independent sources require Jupiter’s magnetic field to align with Earth just so in order for us to hear them. And the Io-dependent sources? Well, they depend on Io, one of Jupiter’s moons. Jupiter’s magnetic field has to align with Earth, and Io has to be in the proper phase of its orbit.

I’m not sure why I think the decametric radio emissions would sound like dubstep. Click here, here, or here to find out what they actually sound like.

In next week’s edition of Sciency Words, we’ll take a closer look—a much closer look—at Io. It seems this humble little moon does more than adjust Jupiter’s radio emissions. Io wields enormous power and influence over the entire radiation environment surrounding Jupiter.

P.S.: Okay, on second thought, maybe we shouldn’t get too close to Io.

Sciency Words: Patera

Sciency Words PHYS copy

For the last few weeks, we’ve been touring the moons of Jupiter and learning about some of the scientific terms used to describe the weird geological features we’ve found there. Today, we conclude this Jovian moons series with the term:

PATERA

Meet Io, Jupiter’s fifth moon and the inner-most of the Galilean moons. Io, say hello to the nice blog readers.

sp23-queasy-io

Oh jeez. I’m sorry you had to see that. Io is sort of caught in a gravitational tug of war between Jupiter and the other Galilean moons. You’d feel queasy too if you were constantly being yanked back and forth by all that gravity.

The result is that Io is the most volcanically active object in the Solar System. Just about any time you look at Io, its sulfur volcanoes are erupting.

A Caldera by Any Other Name…

Astronomers use the word patera (plural, paterae) when discussing Io’s volcanoes. The term comes from the Latin word for flat dish, and the name is appropriate.

Paterae don’t look much like the kind of volcanoes we typically imagine. They aren’t raised, mountain-like features but rather flattened, crater-like depressions. If you know what a caldera is, a patera is basically the same thing.

How Calderas… I Mean, Paterae… Form

Picture this: somewhere on Io, we find an underground chamber full of a nasty, sulfur-rich brew. The temperature in this chamber rises, and the pressure builds up. Suddenly, an eruption occurs, and Io spews that sulfur mixture all over its surface.

As that subterranean chamber empties, the ground above it starts to sink. The resulting pit-like surface feature is a patera. Or a caldera. They really are the exact same thing. (Here’s a short video demonstrating the caldera/patera formation process).

Paterae are not unique to Io. They’ve also been observed on Mars, Venus, and Titan, among other places. They’re also found on Earth, except you’re not supposed to call it a patera if it’s on Earth.

Patera vs. Caldera: What’s the Difference?

If you really want to, you can use the word caldera when referring to Io’s volcanoes, or similar volcanoes on other worlds. That usage seems to be acceptable. But it is unlikely that you will ever see the word patera used for such features here on Earth.

I think there’s a bit of geocentrism at work here. A lot of planetary features have one name on Earth and some other name everywhere else. You’ll sometimes find Earthly terminology used off-world, because Earth terms are more familiar to the average reader; the reverse is rarely if ever true.

Which is fine. I’m not judging. A little linguistic geocentrism makes sense to me, at least at present. In some distant Sci-Fi future where humanity has spread across the Solar System and beyond… at that point, things like the caldera/patera distinction might seem a bit silly.