Mushballs

I first ran into the concept that not all planets had hard, rocky surfaces -- like Earth, and the ones I was all too familiar with from scientific documentaries like Lost in Space -- when I was about eight.

It was in one of those kids' books about astronomy, and I found the whole thing absolutely fascinating.  Mercury, Venus, Earth, and Mars were small, solid, and made mostly of silicate rocks.  Certainly, the four have their dramatic differences -- airless, scorched Mercury; Venus with its brutally hot, carbon-dioxide-rich atmosphere and clouds of sulfuric acid; temperate, lovely Earth; and chilly, windswept, dusty Mars.  But all four, at least to some extent, fit the picture I'd had of what a planet should look like.

But then the outer four -- Jupiter, Saturn, Uranus, and Neptune -- confounded that completely.

All four are gas giants, massive planets with no solid surface (or, if there is one, it's buried so deep as to be all but inaccessible).  The atmospheres are largely hydrogen, helium, carbon monoxide and dioxide, ammonia, and methane.  They rotate fast -- Jupiter, the largest planet, rotates once on its axis every ten hours -- and this, combined with some serious convection currents, creates enormous storms, the most famous of which is Jupiter's Great Red Spot, which is large enough to swallow the Earth entirely and has wind speeds over four hundred kilometers per hour.

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

Even the gas giants' cores aren't like the Earth's; ours is predominantly iron and nickel, while Jupiter -- and, it is surmised, the other three -- have a core largely composed of hydrogen compressed to the point that its electrons delocalize and it begins to act like a metal.  (This metallic hydrogen core is thought to be the source of Jupiter's enormous magnetic field.)

So my picture of the outer four planets was forever changed.  They were huge, churning blobs of gas, not solid at all.  Saturn, in fact, has such a low overall density that if you could find a swimming pool big enough, it'd float.  Then, my mind was further blown when I was twenty and first saw Carl Sagan's Cosmos, where he suggested that such a planet might still host life -- floating or flying creatures that could ride the wild thermal updrafts, and somehow metabolize the anoxic stew of gases they live in.

What's coolest of all, though, is that our understanding of the gas giants is still being refined.  A study out of the University of California - Berkeley found that certain areas of Jupiter's atmosphere are strangely ammonia-depleted.  This is unexpected -- the constant turbulence, you'd think, would result in uniform mixing, just like stirring a cup of coffee distributes the cream and sugar evenly throughout.  If there are areas low in ammonia, what is keeping them that way?

The researchers found a mechanism that might be responsible.  Updrafts in low-pressure zones might, just as they do on Earth, create hailstorms.  But everything's bigger on Jupiter -- bigger than Texas, even -- and these enormous updrafts allow the formation of huge "mushballs" composed primarily of frozen ammonia and water that, once they are too heavy to keep aloft any more, fall down into the lower layers of the atmosphere, leaving upper regions depleted.

So unlike on Earth, where a three-centimeter hailstone is considered pretty huge, these would be between the size of a softball and a basketball.

"The mushball journey essentially starts about fifty to sixty kilometers below the cloud deck as water droplets," said Chris Moeckel, lead author of the paper on the phenomenon, which appeared in Science Advances this week.  "The water droplets get rapidly lofted all the way to the top of the cloud deck, where they freeze out and then fall over a hundred kilometers into the planet, where they start to evaporate and deposit material down there.  And so you have, essentially, this weird system that gets triggered far below the cloud deck, goes all the way to the top of the atmosphere and then sinks deep into the planet...  Imke [de Pater, Moeckel's advisor] and I both were like, 'There's no way in the world this is true.'  So many things have to come together to actually explain this, it seems so exotic.  I basically spent three years trying to prove this wrong.  And I couldn't prove it wrong."

So Sagan's floaters and flyers would not only have to deal with Jupiter's screaming winds and monstrous lightning storms, they'd have to dodge volleyball-sized hailstones.

Not the most hospitable place in the world.

It's pretty cool that even our own Solar System still has the capacity to amaze us.  The more we learn, the more questions we have.  It's like Neil deGrasse Tyson said; "As our knowledge grows, so too does the perimeter of our ignorance."  And sometimes it's a simple, innocuous-seeming question -- like, "why are some parts of Jupiter's atmosphere low in ammonia?" -- that leads to a huge shift in our picture of how some part of the universe works.

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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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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!]