Requiem for a dead planet

If I had to pick my favorite episode of Star Trek: The Next Generation, the clear winner would be "The Inner Light."  Some classic episodes like "Darmok," "Frames of Mind," "Yesterday's Enterprise," "The Offspring," "Cause and Effect," "Remember Me," "Time's Arrow," "The Chase," and "Best of Both Worlds" would be some stiff competition, but "The Inner Light" not only has a beautiful story, but a deep, heartwrenching bittersweetness, made even more poignant by a tour-de-force performance by Patrick Stewart as Captain Jean-Luc Picard.

If you've not seen it, the plot revolves around the Enterprise encountering a huge space station of some kind, of apparent antiquity, and in the course of examining it, it zaps Captain Picard and renders him unconscious.  What his crew doesn't know is that it's dropped him into a dream where he's not a spaceship captain but an ordinary guy named Kamin, who has a wife and children and a job as a scientist trying to figure out what to do about the effect of his planet's sun, which has increased in intensity and is threatening devastating drought and famine.

As Kamin, he lives for forty years, watching his children grow up, living through the grief of his wife's death and the death of a dear friend, and ultimately grows old without ever finding a solution to his planet's dire circumstances.  All the while, the real Captain Picard is being subjected to ongoing interventions by Dr. Crusher to determine what's keeping him unconscious, and ultimately unsuccessful attempts to bring him out of it.  In the end, which makes me ugly cry every damn time I watch it, Kamin lives to watch the launch of an archive of his race's combined knowledge, realizing that the sun's increase in intensity is leading up to a nova that will destroy the planet, and that their civilization is doomed.  It is, in fact, the same archive that the Enterprise happened upon, and which captured Picard's consciousness, so that someone at least would understand what the civilization was like before it was wiped out tens of thousands of years earlier.

"Live now," Kamin says to his daughter, Maribol.  "Make now always the most precious time.  Now will never come again."

And with that, Picard awakens, to find he has accumulated four decades of memories in the space of about a half-hour, an experience that leaves a permanent mark not only on his mind, but his heart.

*brief pause to stop bawling into my handkerchief*

I was immediately reminded of "The Inner Light" by a paper I stumbled across in Nature Astronomy, called, "Alkali Metals in White Dwarf Atmospheres as Tracers of Ancient Planetary Crusts."  This study, led by astrophysicist Mark Hollands of the University of Warwick, did spectroscopic analysis of the light from four white dwarf stars, which are the remnants of stellar cores left behind when Sun-like stars go nova as their hydrogen fuel runs out at the end of their lives.  In the process, they vaporize any planets that were in orbit around them, and the dust and debris from those planets accretes into the white dwarf's atmosphere, where it's detectable by its specific spectral lines.

In other words: the four white dwarfs in the study had rocky, Earth-like planets at some point in their past.

"In one case, we are looking at planet formation around a star that was formed in the Galactic halo, 11-12.5 billion years ago, hence it must be one of the oldest planetary systems known so far," said study co-author Pier-Emmanuel Tremblay, in an interview in Science Daily.  "Another of these systems formed around a short-lived star that was initially more than four times the mass of the Sun, a record-breaking discovery delivering important constraints on how fast planets can form around their host stars."

This brings up a few considerations, one of which has to do with the number of Earth-like planets out there.  (Nota bene: by "Earth-like" I'm not referring to temperature and surface conditions, but simply that they're relatively small, with a rocky crust and a metallic core.  Whether they have Earth-like conditions is another consideration entirely, which has to do with the host star's intrinsic luminosity and the distance at which the planet revolves around it.)  In the famous Drake equation, which is a way to come up with an estimate of the number of intelligent civilizations in the universe, one of the big unknowns until recently was how many stars hosted Earth-like planets; in the last fifteen years, we've come to understand that the answer seems to be "most of them."  Planets are the rule, not the exception, and as we've become better and better at detecting exoplanets, we find them pretty much everywhere we look.

When I read the Hollands et al. paper, I immediately began wondering what the planets around the white dwarfs had been like before they got flash-fried as their suns went nova.  Did they harbor life?  It's possible, although considering that these started out as larger stars than our Sun, they had shorter lives and therefore less time for life to form, much less to develop into a complex and intelligent civilization.  And, of course, at this point there's no way to tell.  Any living thing on one of those planets is long since vaporized along with most of the planet it resided on, lost forever to the ongoing evolution of the cosmos.

If that's not gloomy enough, it bears mention that this is the Earth's ultimate fate, as well.  It's not anything to worry about (not that worry would help in any case) -- this eventuality is billions of years in the future.  But once the Sun exhausts its supply of hydrogen, it will balloon out into a red giant, engulfing the inner three planets and possibly Mars as well, then blow off its outer atmosphere (that explosion is the "nova" part), leaving its exposed core as a white dwarf, slowly cooling as it radiates its heat out into space.

Whether by that time we'll have decided to send our collective knowledge out into space as an interstellar archive, I don't know.  In a way, we already have, albeit on a smaller scale than Kamin's people did; Voyager 2 carries the famous "golden record" that contains information about humanity, our scientific knowledge, and recordings of human voices, languages, and music, there to be decoded by any technological civilization that stumbles upon it.  (It's a little mind-boggling to realize that in the 48 years since Voyager 2 was launched, it has traveled about 20,000,000,000 kilometers, so is well outside the perimeter of the Solar System; and that sounds impressive until you realize that's only 16.6 light hours away, and the nearest star is 4.3 light years from us.)

So anyhow, those are my elegiac thoughts on this August morning.  Dead planets, dying stars, and the remnants of lost civilizations.  Sorry to be a downer. If all this makes you feel low, watch "The Inner Light" and have yourself a good cry.  It'll make you feel better.

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Piercing the clouds

One of the most unusual stories that H. P. Lovecraft ever wrote is "In the Walls of Eryx."  It isn't his usual fare of soul-sucking eldritch nightmares from the bubbling chaos at the center of the universe; in fact, it's his only real, honest-to-Asimov science fiction story.  It centers around a human colony on Venus, devoted to mining a kind of crystal that can be used for propulsion.  There's an intelligent native species -- reptilian in appearance -- who was content to let the humans bump around in their space suits (Lovecraft at least got right that the atmosphere would be toxic to humans) until the humans started killing them.  At that point, they started fighting back -- and setting traps.

The story centers around a crystal hunter who is out on an expedition and sees a huge crystal in the hands of a (human) skeleton.  He goes toward it, and runs face-first into an unseen obstacle -- completely transparent walls, slick (and therefore unclimbable) and four meters tall (so unjumpable).  The problem is, when he tries to back out, he's already moved around a bit, and doesn't retrace his steps perfectly.

Then he runs into another wall.

What's happened is that he's stumbled into an invisible labyrinth.  And how do you find your way out of a maze if you can't see it?  You'll just have to read it.  It's only a dozen or so pages long, and is one of the neatest (and darkest) puzzle-box stories you'll ever pick up.

It's been known since Lovecraft's time ("In the Walls of Eryx" was written in 1936) that Venus was covered by clouds, and its surface was invisible from Earth.  Of course, a solid mantle of clouds creates a mystery about what's underneath, and speculation ran wild.  We have Lovecraft's partially-correct solution -- a dense, toxic atmosphere.  Carl Sagan amusingly summed up some of the early thinking on Venus in the episode "Heaven and Hell" from his groundbreaking series Cosmos: "I can't see a thing on the surface of Venus.  Why not?  Because it's covered with a dense layer of clouds.  Well, what are clouds made of?  Water, of course.  Therefore, Venus must have an awful lot of water on it.  Therefore, the surface must be wet.  Well, if the surface is wet, it's probably a swamp.  If there's a swamp, there's ferns.  If there's ferns, maybe there's even dinosaurs...  Observation: I can't see anything.  Conclusion: dinosaurs."

Of course, reputable scientists didn't jump to these kinds of crazy pseudo-inferences.  As Neil deGrasse Tyson points out, "If you don't know, then that's where your conversation should stop.  You don't then say that it must be anything."  (It's not a coincidence that Tyson was the host of the reboot of Cosmos that appeared a few years ago.)

The first hint that Venus was not some lush tropical rain forest came in the late 1950s, when it was discovered that there was electromagnetic radiation coming from Venus that only made sense if the surface was extremely hot -- far higher than the boiling point of water.  This was confirmed when the Soviet probe Venera 9 landed on the surface, and survived for 127 minutes before its internal circuitry fried.

In fact, saying it's "hot" is an understatement of significant proportions.  The average surface temperature is 450 C -- 350 degrees higher than the boiling point of water, and hot enough to melt lead.  The atmosphere is 96.5% carbon dioxide (compared to 0.04% in the Earth's atmosphere), causing a runaway greenhouse effect.  Most of the other 3.5% is nitrogen, water vapor, and sulfur dioxide -- the latter being the rotten-egg chemical that, when mixed with water, creates sulfuric acid.

Yeah.  Not such a hospitable place.  Even for crystal-loving intelligent reptiles.

Photograph from the surface of Venus [Image is in the Public Domain, courtesy of NASA/JPL]

But there's still a lot we don't know about it, which is why at the meeting of the American Geophysical Union, there was a proposal to send a probe to our nearest neighbor.  But this was a probe with a difference; it would be attached to a balloon, which would keep it aloft, perhaps indefinitely given the planet's horrific convection currents.  From there, we could not only get photographs, but more accurate data on the atmospheric chemistry, and possibly another thing as well.

One of the things we don't know much about is the tectonics of the planet's surface.  There are clearly a lot of volcanoes -- unsurprising given how hot it is from other causes -- but whether the crust is shifting around the way it does on Earth is not known.  One way to find out would be looking for "venusquakes" -- signs that the crust was unstable.  But how to find that out when probes on the surface either melt or get dissolved by the superheated sulfuric acid?

The cool suggestion was that because of the atmosphere's density, it might be "coupled" to the surface.  So if something shook the surface -- a venusquake or volcanic eruption -- those waves might be transferred to the atmosphere.  (This effect is insignificant on Earth because our atmosphere is far, far less dense.)  Think of a plate with a slab of jello on it -- if you shake the plate, the vibrations are transferred into the jello because the whole thing is more or less stuck together, so the surface of the jello wobbles in resonance.

An airborne probe might be able to tell us something about Venus's geology, which is pretty awesome.  It appeals not only to my fascination with astronomy, but my love of a good mystery, which the second planet definitely is.

So I hope this project gets off the ground, both literally and figuratively.  Even if it's unlikely to detect anything living -- reptilian or not -- we could learn a great deal about what happens when the carbon dioxide levels start undergoing a positive feedback loop.

A scenario we all would like very much not to repeat here at home.

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The barrage

At the last Tompkins County Friends of the Library Used Book Sale, I picked up a copy of Donald Yeomans's fascinating book titled Near-Earth Objects (which has the rather alarming subtitle, Finding Them Before They Find Us).  Yeomans has impeccable credentials -- senior fellow with NASA's Jet Propulsion Laboratory, manager/supervisor of the Near-Earth Object Program Office and Solar System Dynamics Group, and researcher with the Deep Impact Project that investigates the composition, origins, and trajectories of comets.  His book is about the potential for a significant asteroid or comet strike on Earth -- and, more importantly, how we might find potentially hazardous orbiting objects soon enough to have a chance to avert the collision.

As Canadian astronaut Chris Hadfield put it, "The dinosaurs went extinct because they didn't have a space program."

One of the topics in Yeomans's book is the history of impacts, including the famous one that ended the Mesozoic Era.  But his timeline goes back a great deal further than that; one of the sections is devoted to a period called the Late Heavy Bombardment -- on the order of four billion years ago -- during which it is thought that the Earth got absolutely pummeled.

What caused this barrage?  Well, first of all, it must be stated that not all scientists even think it happened.  The geological processes on the Earth's surface have erased most of the evidence.  Studies of cratering on the Moon (which presumably would also have gotten clobbered during the same period) have yielded conflicting results; Patrick Boehnke and Mark Harrison, of the University of California, wrote a paper back in 2016 suggesting that the radioisotope dating of rocks from the Moon supported a uniformly decreasing impact rate over its history (i.e., no sudden spike about four billion years ago).

Other researchers disagree.  Three of the largest impact basins on the Moon, the Mare Imbrium, Mare Serenitatis, and Mare Nectaris, all appear to date from right around the time of the hypothesized bombardment.  If the same happened on Earth, it was cataclysmic -- turning large areas of the Earth's crust into molten lava, and vaporizing huge volumes of water in the early oceans.

[Image licensed under the Creative Commons CC-BY-SA, from https://ancient-life-and-history-earth.fandom.com/wiki/Late_Heavy_Bombardment]

Where it gets interesting is the explanation for why the Late Heavy Bombardment happened -- if it did.  The whole thing hinges on a bit of physics that falls into the "stuff that I theoretically knew, but never really thought about" department.

The orbital path of a planet (or asteroid, or comet, or whatever) remains stable as long as nothing adds or removes energy from it.  If something subtracts energy, the orbit becomes smaller; if something adds energy, the orbit gets bigger.  Enough added energy, and it achieves escape velocity and is ejected from the system altogether.  But what would itself have enough energy to interact with something the size of a planet in such a way as to make any difference?

Back in the early history of the Solar System, there was a clutter of debris left over from its formation.  We still have three major bands of it left -- the Asteroid Belt between Mars and Jupiter, the Kuiper Belt beyond the orbit of Neptune, and the Oort Cloud way out past the orbit of Pluto.  There are few asteroids left in the vicinity of the planets, because any that were there were swept up gravitationally.  In fact, that's one of the requirements for an object to be classified as a planet; that it clear the space near it of asteroids.  (This is the characteristic that caused Pluto to get demoted.)

But four billion years ago, there was a great deal more debris around.  Any large-ish asteroids that got near a planet resulted in their giving a gravitational yank on each other; if the asteroid was ahead of the planet, it had a bit of its energy stolen by the planet (making the planet's orbital axis get bigger); if it passed behind the planet, the reverse happened (making the planet's orbital axis shrink).  Well, according to the models described by Yeomans, eventually the pushing and pulling by all of the asteroids added up, and a curious thing happened.

The two largest planets, Jupiter and Saturn, had their orbits altered until they were in a highly stable configuration called a 2:1 orbital resonance.  

What this means is that they were in a pattern where Saturn's orbital period was exactly twice Jupiter's.  (They're still close to that; Saturn orbits the Sun once every 29.4 years, and Jupiter once every 11.9 years.)  But when they were in perfect 2:1 resonance, they reinforced each other's gravitational influence on the outer planets, Uranus and Neptune, giving them a kick every time they lined up -- a little like a kid on a playground swing kicking off every time they pass the ground.

This did two things.  First, it gave energy to Uranus and Neptune, making their orbits bigger, moving them outwards.  Second, it subtracted energy from Jupiter and Saturn, making their orbits smaller (and eventually destroying the resonance).  But the important one here is Neptune, because the increase of its orbit moved it out into a region of space that hadn't been cleared of debris.  When Neptune slipped outward into the inner Kuiper Belt, around four billion years ago, this had the effect of slingshotting a great deal of that debris into the inner Solar System...

... turning Earth into a gigantic bullseye for meteor strikes.

So it's fascinating that if the Late Heavy Bombardment actually did occur, there's a good model for what might have caused it.

The good news is that now that Jupiter and Saturn are no longer in resonance, Neptune is more or less staying put, so any further target practice is unlikely.  Doesn't mean we're out of the woods completely, of course.  Yeomans's whole book is about the possibility of asteroid strikes.

But at least it looks like the barrage is a thing of the past.

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The cotton-candy planet

There's a general pattern you see in astrophysics, which arises from the fact that gravity is both (1) always attractive, never repulsive, and (2) extremely weak.

It's hard to overstate the "extremely weak" bit.  The next strongest of the four fundamental forces, electromagnetism, is 36 orders of magnitude stronger; that is, the electromagnetic force is 1,000,000,000,000,000,000,000,000,000,000,000,000 times more powerful than gravity.  This may seem odd and counterintuitive, since the gravitational pull on your body seems pretty damn strong (especially when you're tired).  But think about it this way; if you use a refrigerator magnet to pick up a paper clip, that little magnet is able to overcome the force of the entire Earth pulling on the clip in the opposite direction.

The practical result of these two features of gravity is that at small scales and low masses, the effects of gravity are essentially zero.  If I'm picking up a book, I don't have to adjust for the negligible gravitational attraction between myself and the book, only the attraction between the book and the enormous mass of the Earth.  On the largest scales, too, the effects of gravity more or less even out; this is called the flatness problem, and is something I dealt with in more detail in a recent post.  (Plus, on these cosmic scales, the force of expansion of spacetime itself -- something that's been nicknamed dark energy -- takes over.)

It's at mid-range scales that gravity becomes seriously important -- objects the size of planets, stars, and galaxies.  And there, the other feature of gravity kicks in; that it always attracts and never repels.  (Whatever Lost in Space may have had to say about anti-gravity, there's never been evidence of any such thing.)  So for objects between the size of planets and galaxies, gravity always wins unless there is some other force opposing it.

This, in fact, is how stars work; the pull of gravity from their mass causes the matter to collapse inward, heating them up until the fusion of hydrogen starts in the core.  This generates heat and radiation pressure, a balancing force keeping the star in equilibrium.  Once the fuel runs out, though, and that outward force diminishes, gravitational collapse resumes -- and the result is a white dwarf, a neutron star, or a black hole, depending on how big the star is.

All of this is just a long-winded way of saying that if you've got a mass big enough to form something on the order of a planet or star, it tends to fall inward and compress until some other force stops it.  That's why the insides of planets and stars are denser than the outsides.

Well, that's how we thought it worked.

The latest wrench in the mechanism came from the discovery of a planet called WASP-193b orbiting a Sun-like star about 1,200 light years away.  On first glance, WASP-193b looks like a gas giant; its diameter is fifty percent larger than Jupiter's.  So far, nothing that odd; exoplanet studies have found lots of gas giants out there.

But... the mass of WASP-193b is only one-seventh that of Jupiter, giving it the overall density of cotton candy.

So I guess in a sense it is a gas giant, but not as we know it, Jim.  At an average density of 0.059 grams per cubic centimeter, WASP-193b would float on water if you could find an ocean big enough.  Plus, there's the problem of what is keeping it from collapsing.  A mass one-seventh that of Jupiter is still an impressive amount of matter; its gravitational pull should cause it to pull together, decreasing the volume and raising the density into something like that of the planets in our own Solar System.  So there must be something, some force that's pushing all this gas outward, keeping it... fluffy.  For want of a better word.  

But what that force might be is still unknown.

"The planet is so light that it's difficult to think of an analogous, solid-state material," said Julien de Wit of MIT, who co-authored the study, in an interview with ScienceDaily.

[Image licensed under the Creative Commons NOIRLab/NSF/AURA/J. da Silva/Spaceengine/M. Zamani, Artist impression of ultra fluffy gas giant planet orbiting a red dwarf star, CC BY 4.0]

"WASP-193b is the second least dense planet discovered to date, after Kepler-51d, which is much smaller," said Khalid Barkaoui, of the Université de Liège's EXOTIC Laboratory and first author of the paper, which was published in Nature Astronomy last week.  "Its extremely low density makes it a real anomaly among the more than five thousand exoplanets discovered to date.  This extremely-low-density cannot be reproduced by standard models of irradiated gas giants, even under the unrealistic assumption of a coreless structure."

In short, the astrophysicists still don't know what's going on.  Twelve hundred light years from here is what amounts to a planet-sized blob of cotton candy orbiting a Sun-like star.  I'm sure that like the disappearing star from my post two days ago, the theorists will be all over this trying to explain how it could possibly happen, but thus far all we have is a puzzle -- a massive cloud of matter that is somehow managing to defy gravity.

As Shakespeare famously observed, there apparently are more things in heaven and earth than are dreamt of in our philosophy.

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Water worlds

Water is one of those things that seems ordinary until you start looking into it.

The subject always puts me in mind of the deeply poignant Doctor Who episode "The Waters of Mars," which has to be in my top five favorite episodes ever.  (If you haven't seen it, you definitely need to, even if you're not a fanatical Whovian like I am -- but be ready for the three-boxes-of-kleenex ending.)  Without giving you any spoilers, let's just say that the Mars colonists shouldn't have decided to use thawed water from glaciers for their drinking supply.

Once things start going sideways, the Doctor warns the captain of the mission, Adelaide Brooke, that trying to fight what's happening is a losing battle, and says it in a truly shiver-inducing way: "Water is patient, Adelaide.  Water just waits.  Wears down the cliff tops, the mountains.  The whole of the world.  Water always wins."

Even beyond science fiction, water has some bizarre properties.  It's one of the only substances that gets less dense when you freeze it -- if water was like 99% of the compounds in the world, ice would sink, and lakes and oceans would freeze from the bottom up.  Compared to most other liquids, it has a sky-high specific heat (ability to absorb heat energy without much increase in temperature) and heat of vaporization (the heat energy required for it to evaporate), both of which act not only to allow our body temperature easier to regulate, it makes climates near bodies of water warmer in winter and cooler in summer than they otherwise would be.  It's cohesive, which is the key to how water can be transported a hundred meters up the trunk of a redwood tree, and is also why a bellyflop hurts like a mofo.  It's highly polar -- the molecules have a negatively-charged side and a positively-charged side -- making it an outstanding solvent for other polar compounds (and indirectly leading to several of the other properties I've mentioned).

And those are the characteristics water has at ordinary temperatures and pressures.  If you start changing either or both of these, things get weirder still.  In fact, the whole reason the topic comes up is because of a paper in Astrophysical Journal Letters called "Irradiated Ocean Planets Bridge Super-Earth and Sub-Neptune Populations," by astrophysicist Olivier Mousis of Aix-Marseille University, about a very strange class of planets where water is in a bizarre state where it's not quite a liquid and not quite a gas.

This state is called being supercritical -- where a fluid can seep through solids like a gas but dissolve materials like a liquid.  For water, the critical point is about 340 C and a pressure 217 times the average atmospheric pressure at sea level, so nothing you'll run into under ordinary circumstances.  This weird fluid has a density about a third that of liquid water at room temperature -- way more dense than your typical gas and way less than your typical liquid.

Mousis et al. have found that some of the "sub-Neptune" exoplanets that have been discovered recently are close enough to their parent stars to have a rocky core surrounded by supercritical water and a steam-bath upper atmosphere -- truly a strange new kind of world even the science fiction writers don't seem to have anticipated.  One of these exoplanets -- K2 18b, which orbits a red dwarf star about 110 light years from Earth -- fits the bill perfectly, and in fact mass and diameter measurements suggest it could be made up of as much as 37% water.

So there you are -- some strange features of a substance we all think we know.  Odd stuff, water, however familiar it is.  Even if you don't count the extraterrestrial contaminants that Captain Brooke and her crew had to contend with.

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The dunes of Io

By anyone's standards, Jupiter's moon Io is a strange place.  It is by far the most geologically-active body in the Solar System, which is extremely unusual for an object its size.  Since tectonic forces are created by heat generated in the core, and smaller objects radiate away heat faster, it was thought that most planetary moons should be tectonically dead -- essentially, frozen in place.

What keeps the fires in Io going are the tidal forces between Jupiter and the other three "Galilean" moons (so called because they were first spotted by Galileo Galilei in January of 1610, and were instrumental in his championing of the heliocentric model of the Solar System).  But from earthbound telescopes all four just looked like points of light, despite the fact that as moons go, they're pretty big.  In fact, the largest of them -- Ganymede -- is bigger than Mercury, with a radius of 2,634 kilometers (as compared to Mercury's 2,440).  The four, the two aforementioned plus Europa and Callisto, were all named for various of Zeus's lovers, which meant astronomers had an extensive list of names to choose from, given that 95% of Greek mythology was driven by Zeus's inability to keep his toga on.

In any case, the push-and-pull of the gravitational forces from Jupiter and its moons stretches Io, and the friction thus created generates enough heat to keep its core (thought to be made mostly of iron, like Earth's) molten.  This thermal energy drives tectonic forces that dwarf the most violent volcanoes and earthquakes here on our planet.  Io has extensive lava flows, some over five hundred kilometers across.  Its volcanoes have ejected so much debris that there is a plasma ring surrounding Jupiter, sketching out Io's orbit.

We got our first good images of Io from Voyager 1 and Voyager 2 in 1979, and from its brightly-colored, pockmarked surface astronomers said it "looked like a moldy pizza" -- a vivid image that is certainly apt enough:

An image of Io taken, appropriately enough, by the spacecraft Galileo in 1995 [Image is in the Public Domain courtesy of NASA/JPL]

The bright yellows and oranges come from crystalline sulfur, which is abundant on the moon's surface.  Also common on its surface is sulfur dioxide, which at Earth's surface temperatures is a colorless gas that smells like rotten eggs; at Io's temperatures, averaging at 110 K (about -160 C), it's a crystalline solid.  The rest is mostly made up of silicate rock and sand.

There's still a lot we don't know about this peculiar place.  One of its odd features is that it has dunes, some of them over thirty meters high.  This should be impossible, as dunes are caused by fluid flow -- on Earth, either wind or water -- and Io has essentially no atmosphere and no liquid component of any kind on the surface.  But a recent paper published in Nature Communications explains a way that dunes can form without any wind; once again, it's caused by Io's extreme volcanism.  The study found that if there's at least a ten-centimeter thick layer of sulfur dioxide ice, and it is contacted by the subterranean (well, subionion) lava flows, the ice sublimates rapidly and explosively, blowing plumes of gas and debris at speeds of up to seventy kilometers and hour, reaching as much as two hundred kilometers high.

The force, though, isn't just exerted upwards, it's exerted outward.  This lateral blast moves enough of the sand and rock on the surface to generate Io's extensive dunes.  A combination of two things -- Io's low gravity and lack of an atmosphere -- means that the airborne debris can move a lot farther than a similar flow could do on Earth.  So while at first glance the processes seem similar to what we know of planetary geology, it's (as far as we know) unique in the Solar System.

"In some sense, these [other worlds] are looking more familiar," says George McDonald, a planetary scientist at Rutgers University, who co-authored the study, in an interview with Science News.  "But the more you think about it, they feel more and more exotic."

If you want to experience mystery and wonder, just look up.  The night sky is filled with a myriad places we are only just beginning to understand.  As French physicist and mathematician Jules Henri Poincaré put it, "Astronomy is useful because it raises us above ourselves; it is useful because it is grand; …  It shows us how small is man's body, how great his mind, since his intelligence can embrace the whole of this dazzling immensity, where his body is only an obscure point, and enjoy its silent harmony."

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Mysterious planet

You never hear people talking about the planet Neptune much.

The other planets are all famous for something or another.  Mercury is the closest to the Sun; Venus is ridiculously hot; Mars has been the subject of repeated visits; Jupiter's the biggest; Saturn has rings; and Uranus is best known for being a name you can't say without all the immature people giggling. 

To be fair, the unfortunately-named Uranus has some fascinating features, the most obvious of which is its axial tilt.  Its rotational axis is tipped at a bit over ninety degrees -- so it, in effect, rolls around its orbit on its side.  This means that at its summer solstice, its northern hemisphere is almost entirely illuminated all day long, and the entire southern hemisphere is in the dark; the opposite is true on the winter solstice.  (And given that its orbital period is 84 Earth years long, its winters are even longer than the ones we have here in upstate New York.)

But Neptune?  Other than the fact that it's a gas giant, and very far out in the Solar System, most people don't know much about it.

That's a shame, because it's a pretty interesting place.  Being about 1.5 times farther away from the Sun than Uranus, it's got a much longer year, at 164.8 Earth years.  It's really cold, with an average temperature somewhere around 70 K (-200 C, give or take).  Also, it's an interesting color -- a really deep, rich blue, something we didn't know until the first good images came back from the Voyager 2 flyby almost a little over thirty years ago.  Some of the color apparently comes from crystals of methane, but according to NASA, it's way deeper blue to be accounted for solely from that.  Their page on the planet says, "Uranus' blue-green color is also the result of atmospheric methane, but Neptune is a more vivid, brighter blue, so there must be an unknown component that causes the more intense color that we see.  The cause of Neptune's bluish tinge remains a mystery."

[Image is in the Public Domain courtesy of NASA/JPL]

What brings this up is a study out of the University of Leicester showing that we haven't come close to exploring all of Neptune's oddities.  Currently the planet is in the southern hemisphere's summer; Neptune's axial tilt is a little over 28 degrees, so more than the Earth's (at 23.5) but nowhere near as tilted as Uranus (at 97.7).  So as with the Earth, when the southern hemisphere is pointed toward the Sun, it should be slowly warming up.

It's not.  It's cooling down.  The average temperature of the upper atmosphere in the southern hemisphere has dropped by 8 C.  (Remember that being a gas giant, Neptune has no well-defined surface.)  Even odder, there one place that's warming -- the planet's south pole, where the average temperature has gone up by 11 C.

These are not small changes, especially given how big Neptune is (seventeen times the mass of the Earth).  And the astronomers have no idea what's causing it.  It sounds like something that could be driven by convection -- atmospheric turnover, where warmer gases from lower down in the atmosphere rise, displacing colder, denser gases as they do so -- but that's a hell of a big convection cell if it's affecting the entire southern hemisphere of the planet.

Of course, when it comes to moving stuff around, Neptune is pretty good at it.  It has the fastest winds ever clocked in the Solar System (at a little over 1,900 km/hr).  An enormous storm called the "Great Dark Spot" was spotted by Voyager 2 in 1989 -- but by 1994, it had completely disappeared.

"I think Neptune is itself very intriguing to many of us because we still know so little about it," said astronomer Michael Roman, who was lead author on the paper, which appeared this week in The Planetary Science Journal.  "This all points towards a more complicated picture of Neptune’s atmosphere and how it changes with time."

So the most distant planet from the Sun is still largely a mystery, and this week's paper just added to its peculiarities.  Amazing that since its discovery by German astronomer Johann Gottfried Galle in 1846, we are still largely in the dark about what makes it tick.

And I, for one, find that absolutely fascinating.

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The eccentric heavens

For a lot of people, the most disquieting thing about science is the way it's moved humanity farther and farther from its position as the center of the universe.

It's why the heliocentric model met with such resistance.  That the Earth was at the center, and all celestial objects move in circles around it, seemed not only common sense but to fit with the biblical view of the primacy of humans as being created in the image of God.  Copernicus and Galileo ran afoul of the church because their findings contradicted that -- especially when Galileo was the first to see the four largest moons of Jupiter (now known as the "Galilean moons" in his honor), and it was clear they were circling Jupiter and not the Earth -- meaning there are celestial objects that don't obey the model of the entire universe being geocentric.

Another blow was dealt to this idea when Johannes Kepler used data by Danish observational astronomer Tycho Brahe to show that the planets weren't even in circular orbits -- i.e., the heavens were not neat, tidy, and divine, with everything moving in "perfect circles."  That idea didn't die easily.  It'd been known since the time of Ptolemy (second century C.E.) that perfectly circular orbits with the Earth at the center didn't produce predictions that matched the actual positions of the planets, so Ptolemy and others tried desperately to salvage the model by having them move in "epicycles" -- smaller circles that loop-the-loop around a point that itself travels in a circle around the Earth.  But that didn't quite do it, either.  Instead of scrapping the model, Ptolemy introduced epicycles around the epicycles, resulting in an orbital pattern so complex it's almost funny (but still, supposedly, "perfect").

The Ptolemaic model of the universe [Image is in the Public Domain]

But that didn't quite work either, even if you followed Copernicus's lead, put the Sun at the center, and adjusted the planetary orbits accordingly.  The discrepancies bothered Kepler until he finally had to concede that the objects in the Solar System didn't move in circles around the Sun, but in "imperfect" ellipses with the Sun at one focal point.  A measure of how far off the orbit is from being circular -- the "flatness" of the ellipse, so to speak -- is called the eccentricity.  Some planets have very low eccentricity; their orbits are nearly circular.  Of the planets in the Solar System, Venus has the lowest eccentricity, at 0.0068.  Mercury has the highest, at 0.2056.

There's no reason why it couldn't go a lot higher, though.  Comets have highly eccentric orbits; Halley's Comet, for example, has an orbital period of 76 years and an eccentricity of 0.9671.

Could an actual planet have a very eccentric orbit?  Yes, but it would create the climate from hell, hot when it's at the perihelion of its orbit and freezing cold when it's at the aphelion.  Even the old Lost in Space looked at this possibility; very early on, the Robinsons find that the average temperature on the planet where they're stranded is dropping, and the Robot figures out this is because the planet is in a highly elliptical orbit.  This means, of course, that if they survive the intense cold, they're in for a period of intense heat when the planet reaches the other side of its orbit.  Unfortunately, this clever plot point got fouled up because the writers evidently didn't know the difference between a planet's rotation and its revolution, so when the peak cold and peak heat come, it only lasts for a few minutes.  For example, in a highly dramatic scene, the intrepid family take shelter under reflective tarps when the planet's sun is at its closest, and some of the tarps burst into flame, but five minutes later, things are cooling off.

Disaster averted, unless you count the traumatic eye-rolls experienced by viewers who knew even the rudiments of astronomy.

The reason this comes up is because of the discovery of an exoplanet with the highest eccentricity known.  A paper in Astronomy & Astrophysics last week describes a planet orbiting a red dwarf star about 188 light years away, which is over twice the size of the Earth, and has an orbital eccentricity of about 0.5.  This means that in its 35-day orbit, the average temperature fluctuates between -80 C and 100 C -- a frozen wasteland at aphelion and a boiling blast furnace at perihelion, with brief periods in between where the temperature might be tolerable.

"In terms of potential habitability, this is bad news," said Nicole Schanche, an astronomer at the University of Bern and lead author of the paper, in what has to be understatement of the year.

So the whole "Goldilocks zone" issue for finding habitable exoplanets -- an orbital distance resulting in temperatures where water could exist as a liquid, which isn't too hot or too cold, but "just right" -- isn't as simple as it sounds.  The average temperature might be in the right range, but if the planet has an eccentric orbit, the average may not tell you much.  It's like the old quip that if you have one foot encased in ice and the other one in a pot of boiling water, on average you're comfortable.

Not only that, but there's the problem of tidal locking -- when the rotation and revolution rate are equal, so the same side of the planet always faces its sun.  Once again, this might result in an average temperature that is reasonably good, but only because one side is getting continuously cooked while the other is in the deep freeze.  It might be possible to live on the boundary between the light and dark sides -- a place where the planet's star is forever on the horizon -- but there, you'd find a different problem.  Because of the process of convection, in which fluids flow in such a way as to distribute heat evenly, on that twilight margin there'd be catastrophic upper-level winds from the hot to the cold side and equally strong ones at the surface from the cold to the hot side, putting that thin zone smack in the center of the Convection Cell from Hell and rendering even that area effectively uninhabitable.

So we're lucky to live where we do.  Or, more accurately, if the Earth had any of the aforementioned problems, we wouldn't be here.  But this further reinforces my awareness of what a beautiful, awe-inspiring, and scarily inhospitable place the universe is.  And whether there are other places out there that are as clement as the Earth, where life as we know it could evolve and thrive, remains very much to be seen.

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Like many people, I've always been interested in Roman history, and read such classics as Tacitus's Annals of Imperial Rome and Suetonius's The Twelve Caesars with a combination of fascination and horror.  (And an awareness that both authors were hardly unbiased observers.)  Fictionalized accounts such as Robert Graves's I, Claudius and Claudius the God further brought to life these figures from ancient history.

One thing that is striking about the accounts of the Roman Empire is how dangerous it was to be in power.  Very few of the emperors of Rome died peaceful deaths; a good many of them were murdered, often by their own family members.  Claudius, in fact, seems to have been poisoned by his fourth wife, Agrippina, mother of the infamous Nero.

It's always made me wonder what could possibly be so attractive about achieving power that comes with such an enormous risk.  This is the subject of Mary Beard's book Twelve Caesars: Images of Power from the Ancient World to the Modern, which considers the lives of autocrats past and present through the lens of the art they inspired -- whether flattering or deliberately unflattering.

It's a fascinating look at how the search for power has driven history, and the cost it exacted on both the powerful and their subjects.  If you're a history buff, put this interesting and provocative book on your to-read list.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

The celestial dance

It's interesting how the approach to science has changed in the last four centuries.

It's easy to have the (mistaken) impression that as long as we humans have been doing anything scientific, we've always done it the same way -- looked at the evidence and data, then tried to come up with an explanation.  But science in Europe before the eighteenth-century Enlightenment was largely done the other way around; you constructed your model from pure thought, based on a system of how you believed things should act, and once you had the model, you cast about for information supporting it.

It's why Aristotle's statement that the rate of speed of a falling object is directly proportional to its mass stood essentially unchallenged for over a millennium and a half despite the fact that it's something any second grader could figure out was wrong simply by dropping two different-sized rocks from the same height and observing they hit the ground at exactly the same time.  As odd as it is to our twenty-first century scientific mindset, the idea of figuring out if your claim is correct by testing it really didn't catch on until the 1700s.  Which is why the church fathers got so hugely pissed off at Galileo; using a simple experiment he showed that Aristotle got it wrong, and then followed that up by figuring out how things up in the sky moved (such as the moons of Jupiter, first observed by Galileo through the telescope he made).  And this didn't result in the church fathers saying, "Whoa, okay, I guess we need to rethink this," but their putting Galileo on trial and ultimately under permanent house arrest.

That "think first, observe later" approach to science plagued our attempts to understand the universe for a long time after Galileo; people first came up with how they thought things should work, often based on completely non-scientific reasons, then looked for data to support their guess.  That we've come as far as we have is a tribute to scientists who were able to break out of the straitjacket of what the Fourth Doctor in Doctor Who called "not altering their views to fit the facts, but altering the facts to fit their views."

One of the best examples of this was the seventeenth-century astronomer Johannes Kepler.  He was a deeply religious man, and lived in a time when superstition ruled pretty much everything -- in fact, Kepler's mother, Katharina (Guldenmann) Kepler, narrowly escaped being hanged for witchcraft.  Kepler, and most other European astronomers from his time and earlier, were as much astrologers as scientists; they expected the heavens to operate by some kind of law of divine celestial perfection, where objects moved in circles (anything else was viewed as imperfect) and their movements had a direct effect on life down here on Earth.

At the beginning, Kepler tried to extend his conviction of the mathematical perfection of the cosmos to the distances at which the planets revolved around the Sun.  He became convinced that the spacing of the planets' orbits was determined by conforming to the five Platonic solids -- cube, dodecahedron, tetrahedron, icosahedron, and octahedron -- convex polyhedra whose sides are made up only of identical equal-sided polygons.  He tried nesting them one inside the other to see if the ratios of their spacing could be made to match the estimated spacing of the planets, and got close, but not close enough.  One thing Kepler had going for him was he was firmly committed to the truth, and self-aware enough to know when he was fudging things to make them fit.  So he gave up on the Platonic solids, and went back to "we don't know why they're spaced as they are, but they still travel in perfect circles" -- until careful analysis of planetary position data by the Danish observational astronomer Tycho Brahe showed him again that he was close, but not quite close enough.

This was the moment that set Kepler apart from his contemporaries; because instead of shrugging off the discrepancy and sticking to his model that the heavens had to move in perfect circles, he jettisoned the whole thing and went back to the data to figure out what sort of orbits did make sense of the observations.  After considerable work, he came up with what we now call Kepler's Laws of Planetary Motion, including that planets move in "imperfect" elliptical, not circular, orbits, with the Sun at one focus.

Start with the data, and see where it drives you.  It's the basis of all good science.

[Image licensed under the Creative Commons Gonfer, Kepler-second-law, CC BY-SA 3.0]

What got me thinking about Kepler and his abandonment of the Platonic-solid-spacing idea was a paper this week in Astronomy & Astrophysics showing that even though Kepler initially was on the wrong track, there are sometimes odd mathematical regularities that pop up in the natural world.  (A well-known one is how often the Fibonacci series shows up in the organization of things like flower petals and the scales of pine cones.)  The paper, entitled "Six Transiting Planets and a Chain of Laplace Resonances in TOI-178," by a team led by Adrien Leleu of the Université de Genève, showed that even though hard data dashed Kepler's hope of the motion of the heavens being driven by some concept of mathematical perfection, there is a weird pattern to the spacing of planets in certain situations.  The patterns, though, are driven not by some abstract philosophy, but by physics.

In physics, resonance occurs when the physical constraints of a system make them oscillate at a rate called the "natural frequency."  A simple example is the swing of a pendulum; a pendulum of a given length and mass distribution only will swing back and forth at one fixed rate, which is why they can be used in timekeeping.  The motion of planets (or moons) is also an oscillating system, and a given set of objects of particular masses and distances from their center of gravity will tend to fall into resonance, the same as if you try to swing a pendulum at a different rate than the rate at which it "wants to go," then let it be, it'll pretty much immediately revert to swinging at its natural frequency.

The three largest moons of Jupiter exhibit resonance; they've locked into orbits that are the most stable for the system, which turns out to be a 4:2:1 resonance, meaning that the innermost (Io) makes two full orbits in the time the next one (Europa) makes a single orbit, and four full orbits in the time it takes for the farthest (Ganymede).

This week's paper found a more complex resonance pattern in five of the planets around TOI-178, a star two hundred light years away in the constellation Sculptor.  It's a 18:9:6:4:3 resonance chain -- the nearest planet orbits eighteen times as the farthest orbits once, the next farthest nine times as the farthest orbits once, and so on.  This pattern was locked in despite the fact that the planets are all quite different from each other; some are small, rocky planets like Earth, others low-density gaseous planets like Neptune.

"This contrast between the rhythmic harmony of the orbital motion and the disorderly densities certainly challenges our understanding of the formation and evolution of planetary systems," said study lead author Adrien Leleu, in an interview with Science Daily.

So the dance of the celestial bodies is orderly, and shows some really peculiar regularities that you wouldn't have guessed.  But unlike Kepler's favored (but ultimately abandoned) idea that the perfect heavens had to be arranged by perfect mathematics, the Leleu et al. paper shows us that those patterns only emerge by analysis of the data itself, rather than the faulty top-down attempt to force the data to conform to the way you think things should be.  Once you open your mind up to going where the hard evidence leads, that's when the true wonders of the universe begin to emerge.

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Just last week, I wrote about the internal voice most of us live with, babbling at us constantly -- sometimes with novel or creative ideas, but most of the time (at least in my experience) with inane nonsense.  The fact that this internal voice is nearly ubiquitous, and what purpose it may serve, is the subject of psychologist Ethan Kross's wonderful book Chatter: The Voice in our Head, Why it Matters, and How to Harness It, released this month and already winning accolades from all over.

Chatter not only analyzes the inner voice in general terms, but looks at specific case studies where the internal chatter brought spectacular insight -- or short-circuited the individual's ability to function entirely.  It's a brilliant analysis of something we all experience, and gives some guidance not only into how to quiet it when it gets out of hand, but to harness it for boosting our creativity and mental agility.

If you're a student of your own inner mental workings, Chatter is a must-read!

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Bridging the Great Divide

One of the main things that separates scientists from the rest of us is that they notice things we would just take for granted.

Gregor Mendel started in the research that eventually would uncover the four fundamental laws of inheritance when he noticed that some traits in pea plants seemed to skip a generation.  Percy Spencer was messing around with vacuum tubes, and noticed that in a certain configuration, they caused a chocolate bar in his pocket to melt -- further inquiry led to the invention of the microwave oven.  French physicist Henri Becquerel discovered radioactivity when he accidentally ruined some photographic plates with what turned out to be a chunk of uranium ore.  Alexander Fleming saved countless lives with the discovery of penicillin -- found because he wondered why a colony of mold on one of his culture plates seemed to be killing the bacteria near it.

I consider myself at least a little above average, savvy-wise, but I don't have that ability -- to look at the world and think, "Hmm, I wonder why that happened?"  Mostly I just assume "that's the way it is" and don't consider it much further, a characteristic I suspect I share with a lot of people.  So here's some recent research about something I've known about since I first started reading junior books on astronomy, when I was maybe ten years old, and never thought was odd -- or even worth giving any thought to.

There's a strange gap, something astronomers call "The Great Divide," between Mars and Jupiter.  The distance between Mars and Jupiter is over twice as great as the diameter of the entire inner Solar System.  In that gap is a narrow band called the Asteroid Belt -- and not a hell of a lot else.

Even more peculiar, when you think about it (which as I said, I didn't), is why inside of the Great Divide all the planets are small, dense, and rocky, and outside of it the planets are low-density gas giants (I do remember being shocked by the density thing as a kid, when I read that Saturn's overall density is lower than that of water -- so if you had a swimming pool big enough, Saturn would float).

[Image is in the Public Domain courtesy of NASA/JPL]

The problem with these sorts of observations, though -- even if you stop to wonder about them -- is that until very recently, we pretty much had a sample size of one Solar System to work with, so there was no way to tell if any particular feature of ours was odd or commonplace.  Even now, with the discovery of so many exoplanets that it's estimated there are a billion in our galaxy alone, we only have tentative information about the arrangement of planets around stars, to determine if there's any sort of pattern there, such as the apparent one in our neck of the woods.

Well, it looks like the physicists may have explained the Great Divide and the compositional difference of the planets on either side of it in one fell swoop.  A team from the Tokyo Institute of Technology and Colorado University have found that the Great Divide may be a relic of a ring of material that formed around the early Sun, and then was pulled apart and essentially "sorted" by the gravitational pulls of the coalescing planets.

The authors write:

We propose... that the dichotomy was caused by a pressure maximum in the disk near Jupiter’s location...  One or multiple such—potentially mobile—long-lived pressure maxima almost completely prevented pebbles from the Jovian region reaching the terrestrial zone, maintaining a compositional partition between the two regions.  We thus suggest that our young Solar System’s protoplanetary disk developed at least one and probably multiple rings, which potentially triggered the formation of the giant planets.

And once the process started, it accelerated, pulling dense, rocky material inward and lightweight, organic-chemical-rich material outward, resulting in a gap -- and an outer Solar System with gas giants surrounding an inner Solar System with small, terrestrial worlds.

"Young stellar systems were often surrounded by disks of gas and dust," said Stephen Mojzsis of Colorado University, who co-authored the paper, which appeared in Nature three weeks ago.  "If a similar ring existed in our own solar system billions of years ago, it could theoretically be responsible for the Great Divide, because such a ring would create alternating bands of high- and low-pressure gas and dust.  Those bands, in turn, might pull the solar system's earliest building blocks into several distinct sinks -- one that would have given rise to Jupiter and Saturn, and another Earth and Mars.

"It is analogous to the way the Continental Divide in the Rocky Mountains causes water to drain one way or another.  That's similar to how this pressure bump would have divided material in the early Solar System...  But that barrier in space was not perfect.  Some outer Solar System material still climbed across the divide.  And those fugitives could have been important for the evolution of our own world...  Those materials that might go to the Earth would be those volatile, carbon-rich materials.  And that gives you water.  It gives you organics."

And ultimately, it gives the Earth life.

So here we have a strange observation that most of us probably shrugged about (if we noticed it at all) that not only was instrumental to the formation of our own Solar System, but might (1) drive the arrangement of planets in star systems everywhere in the universe, and (2) has implications for the origin of life on our own -- and probably other -- worlds.

All of which brings to mind the wonderful quote by Hungarian biochemist Albert von Szent-Györgyi -- "Discovery consists of seeing what everyone has seen, and thinking what nobody has thought."

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This week's Skeptophilia book of the week is a dark one, but absolutely gripping: the brilliant novelist Haruki Murakami's Underground: The Tokyo Gas Attack and the Japanese Psyche.

Most of you probably know about the sarin attack in the subways of Tokyo in 1995, perpetrated by members of the Aum Shinrikyo cult under the leadership of Shoko Asahara.  Asahara, acting through five Aum members, set off nerve gas containers during rush hour, killing fifty people outright and injuring over a thousand others.  All six of them were hanged in 2018 for the crimes, along with a seventh who acted as a getaway driver.

Murakami does an amazing job in recounting the events leading up to the attack, and getting into the psyches of the perpetrators.  Amazingly, most of them were from completely ordinary backgrounds and had no criminal records at all, nor any other signs of the horrors they had planned.  Murakami interviewed commuters who were injured by the poison and also a number of first responders, and draws a grim but fascinating picture of one of the darkest days in Japanese history.

You won't be able to put it down.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]