Encyclopedia Galactica

I was an undergraduate when the original Cosmos first aired.

It was back in 1980, and I still remember being blown away by it all -- the melding of science with animation and gorgeous music, and Carl Sagan's lyrical, almost poetic way of expressing his enduring love for astronomy.  My friends and I always waited excitedly for the next episode to air, and the day afterward spent an inordinate amount of time chatting about what we'd learned.

One of the episodes that resonated the most strongly with me was entitled "Encyclopedia Galactica."  Sagan predicted a day when we'd know so much about the universe that we'd have an encyclopedia of alien planets, each page of which would be accompanied by a list of their physical characteristics -- and types of life forms.  He was unequivocal in his belief that we were not alone in the universe, and that in fact life would turn out to be common.  Not, perhaps, "life as we know it, Jim" -- and much of it almost certainly pre-technological -- but life, he thought, would turn out to be pretty much everywhere we looked.

In the forty-five years since it aired, our detecting equipment has gotten better and better, but we're still up against the Fermi Paradox -- that famous quip from physicist Enrico Fermi who, when told that life was likely to be common in the universe, said, "Then where is everybody?"  Long-time readers of Skeptophilia may recall that a few years ago I did a deeper dive into the Fermi Paradox and the infamous "three f's," but the fact remains that despite getting better and better at astronomy and astrophysics, we still have no incontrovertible evidence of extraterrestrial life (intelligent or otherwise).

But extrasolar planets?  Those are kind of a dime a dozen.  As of this month, there have been a bit over six thousand exoplanets conclusively identified, and some of them have challenged our models of what planets can be.  (I took a look at a few of the weirder ones in a post earlier this year.)  So even if we don't yet have aliens in our back yard, there's been a lot of really cool information discovered -- three examples of which have just come out in the past couple of weeks.

No Andorians yet, more's the pity.

The first is about the TRAPPIST-1 system, which was one of the first multi-planet systems discovered.  Not only that, it has four planets in the "Goldilocks zone" -- the region around the host star that is "just right" for having temperatures where water could be in its liquid state.  (This doesn't mean there is water; just that if other factors were favorable, there could be liquid water.)  Not only that, but we lucked out that TRAPPIST-1 is fairly close (a little over forty light years away, in the constellation of Aquarius), and that its planets' orbits are aligned so that from our perspective, they cross in front of their host star, allowing astrophysicists to use the transits to take a stab at the composition of their atmospheres.

The outstanding YouTuber Dr. Becky Smethurst did a wonderful video explaining how this all works (and why the planet TRAPPIST-1d probably doesn't have an atmosphere), but a capsule summary is that when the planet passes in front of the star, its light passes through the planet's atmosphere (if it has one), and any gases present absorb and scatter characteristic frequencies of light.  Compared to the unobstructed spectrum of the star, those frequencies are then missing (or at least diminished in intensity), and from that information astrophysicists can deduce what might be present in the atmosphere.

Well, the other three planets in the habitable zone -- TRAPPIST-1b, c, and d -- have pretty conclusively been shown to lack an atmosphere.  So it all hinges on 1e, the farthest one out, and a study at the University of Bristol, using data from the James Webb Space Telescope, has said that it cannot rule out the presence of an atmosphere on that one.  Not a ringing endorsement, that, but at least not a categorical no -- so we'll keep our eyes on TRAPPIST-1e and hope future studies will give us good news.

The other two stories are about "rogue exoplanets" -- planets out there floating in space that don't (or at least, don't now) orbit a star.  Whether they formed that way, or started out in a stellar system and then were ejected gravitationally, is unknown (and may well be different in different cases).  These, for obvious reasons, are considered poor candidates for life, but they still are pretty amazing -- and the fact that we know about them at all is a tribute to our vastly improved ability to detect objects out there in interstellar space.

The first one, CHA-1107-7626, is currently accreting material like mad -- something not seen before in an exoplanet, rogue or otherwise.  It is estimated to be between five and ten times the mass of Jupiter, so on the verge of being a "brown dwarf" -- a superplanet that has sufficient mass and pressure to fuse deuterium but not hydrogen.  They emit more energy than they absorb, but don't quite have enough for the nuclear furnace to turn on in a big way.

But if CHA-1107-7626 keeps going the way its going, it may get there.  It's hoovering up an estimated Jupiter's worth of material every ten million years or so, which is the largest accretion rate of any planet-sized object ever observed.  So what we might be witnessing is the very earliest stages of the formation of a new star.

The final study is about the rogue exoplanet SIMP-0136, which came out of Trinity College Dublin and again uses data from JWST.  But this exoplanet is bizarre for two different reasons -- it has vast storms of what amounts to liquid droplets of sand... and it has auroras.

Once again, I'm staggered by the fact that we could detect this from so far away.  The temperature of the surface of the planet is around 1,500 C -- hotter than my kiln at full throttle -- and it has three hundred kilometer per hour winds that blow around bits of molten silica.  But most peculiar of all, the planet's atmosphere shows the characteristic polar light flashes we see down here as auroras.

What's weirdest about that is that -- at least on Earth -- auroras are caused by solar activity, and this planet isn't orbiting a star.  The way they form down here is that the solar wind ionizes gases in the upper atmosphere, and when those ions grab electrons, and the electrons descend back to the ground level, they emit characteristic frequencies of light (the same ones, not coincidentally, that are swiped by gases in the atmospheres of planets during transits).  Red for monoatomic oxygen, green for diatomic oxygen, blue for molecular nitrogen, and so on.

What is ionizing the gases on SIMP-0136?  Astrophysicists aren't sure.  Sandstorms here on Earth can certainly cause static electrical discharges (what we laypeople refer to as "bigass lightning bolts"), so it's possible we're seeing the light emitted from interactions between the molten silica and whatever gases make up the planet's atmosphere.  But it's too soon to be sure.

So even if we haven't yet discovered Skithra or Slitheen or Sontarans or whatnot, we're still adding some pretty amazing things to our Encyclopedia Galactica.  Carl Sagan, as usual, was prescient.  As he put it, "Somewhere, something incredible is waiting to be known."

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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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Down in flames

The more exoplanets we find, the more they challenge our notion of how planets should be.

For the many of us who grew up watching Star Trek and Lost in Space and Doctor Who, it's understandable that we picture planets around other stars as being pretty much like the ones we have here in our own Solar System -- either small and rocky like the Earth, or gas giants like Jupiter and Saturn.

The truth is, there is a far greater variety of exoplanets than we ever could have dreamed of, and every new one we find holds some sort of surprise.  Some of the odder ones are:

• TrES-2b, which holds the record as the least-reflective planet yet discovered.  It's darker than a charcoal briquet.  This led some people to conclude that it's made of dark matter, something I dealt with here at Skeptophilia a while back.  (tl:dr -- it's not.)
• CoRoT-7b, one of the hottest exoplanets known.  Its composition and size are thought to be fairly Earth-like, but it orbits its star so closely that it has a twenty-day orbital period and surface temperatures around 3000 C.  This means that it is likely to be completely liquid, and experience rain made of molten iron and magnesium.
• 55 Cancri e, nicknamed the "diamond planet."  Another "hot super-Earth," this one is thought to be carbon rich, and that because of the heat and pressure, much of the carbon could be in the form of diamonds.  (Don't tell Dr. Smith.)
• PSR J1719−1438, a planet orbiting a pulsar (the collapsed, rapidly rotating core of a giant star).  It has one of the fastest rates of revolution of any orbiting object known, circling its host star in only 2.17 hours.
• V1400 Centauri, a planet with rings that are two hundred times wider than the rings of Saturn.  In fact, they dwarf the planet itself -- the whole thing looks a bit like a pea in the middle of a dinner plate.

We now have a new one to add to the list -- BD+05 4868 Ab, in the constellation of Pegasus.  Only 140 light years away, this exoplanet is orbiting so close to its parent star -- twenty times closer than Mercury is to the Sun -- that its year is only 30.5 hours long.  This proximity roasts the surface, melting and then vaporizing the rock it's made of.  That material is then blasted off the surface by the stellar wind.

So BD+05 4868 Ab is literally evaporating, and leaving a long, comet-like tail in its wake.

The estimate is that each time it orbits, it loses a Mount Everest's worth of rock from its surface.  It's not a large world already, and the researchers say it is on track to disintegrate completely in under two million years.

"The extent of the tail is gargantuan, stretching up to nine million kilometers long, or roughly half of the planet's entire orbit," said Marc Hon of MIT, who co-authored a paper on the planet, which appeared this week in Astrophysical Journal Letters.  "The shape of the transit is typical of a comet with a long tail,.  Except that it's unlikely that this tail contains volatile gases and ice as expected from a real comet -- these would not survive long at such close proximity to the host star.  Mineral grains evaporated from the planetary surface, however, can linger long enough to present such a distinctive tail."

[Image licensed under the Creative Commons Marc Hon et al. 2025, submitted to AAS Journals, BD+05 4868Ab simulation dust cloud (Figure 12), CC BY 4.0]

So we have a new one to add to the weird exoplanet list -- a comet-like planet in the process of going down in flames.  Not a place you'd want to beam your away team to, but fascinating anyhow.

Makes me wonder what the next bizarre find is going to be.  The universe is like that, isn't it?  We think we have it figured out, then it turns around and astonishes us.

I, for one, think that is fantastic.

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The signature

As much as I love the movie Contact, trying to find extraterrestrial life isn't just a matter of tuning in to the right radio frequency.

There's no guarantee that even intelligent life would use radio waves to communicate, and if they did, that they'd do it in such a way that we could decipher the message.  I must admit, though, that the whole "sequence of prime numbers" thing as a beacon was a pretty cool idea; it's hard to imagine a natural phenomenon that would result in blips in a pattern of prime numbers.

Even besides the issue with how exactly a technological species would choose to communicate, there's the problem that this method would miss the vast majority of life that's potentially out there.  Consider the fact that there's been life on Earth for 3.8 billion years, give or take a day or two, and until about a hundred years ago, we weren't producing any radio waves ourselves.  To a civilization two hundred light years away -- so, seeing us as we were two hundred years ago -- Earth would be, to borrow C. S. Lewis's pithy phrase, a completely silent planet, even though there was a thriving biosphere that included at least one intelligent, soon-to-be-technological species.

So except for those presumably few planets that host intelligent beings who communicate kind of like we do, detecting extraterrestrial life is a tricky question.  The most promising approach has been to look for biosignatures -- chemical traces that (as far as we know) can only be produced by living things.  One example on Earth is the fact that our atmosphere contains both oxygen and methane.  Both are highly reactive (especially with each other); to keep stable levels of these gases in the atmosphere requires that something is continuously producing them, because they're constantly being removed by oxidation/reduction reactions.  In this case, photosynthesis and bacterial methanogenesis, respectively, pump them into the atmosphere as fast as they're being destroyed, so the levels remain relatively stable over time.

Two other chemicals that, on the Earth at least, are entirely biological in origin are dimethyl sulfide and dimethyl disulfide.  You've undoubtedly encountered these before; they're partly responsible for the unpleasant smell when you cook cabbage.  They're produced by a variety of living things, including bacteria, plants, and fungi -- dimethyl sulfide is what truffle-hunting pigs are homing in on when they're after truffles. 

Well, data from the James Webb Space Telescope showed that an exoplanet called K2-18b has measurable quantities of both dimethyl sulfide and dimethyl disulfide -- to the point that even the astronomers, who ordinarily have zero patience with the "It's aliens!" crowd, are saying "this is the strongest hint yet of biological life on another planet."

So far, the spectroscopic data that found the chemicals is at a significance level of "3-sigma" -- meaning there's a 0.3% chance that the signal was a statistical fluke (or, put another way, a 99.7% chance that it's the real deal).  It's exciting, but we've seen 3-sigma data do a faceplant before, so I'm trying to restrain myself.  Generally 5-sigma -- a 0.00006% chance of it being a fluke -- is the standard for busting out the champagne.  But even so, this is pretty amazing.

K2-18b is 124 light years away, and is thought to be a "Hycean world" -- an ocean-covered world with a thick, hydrogen-rich atmosphere.  So whatever life is there is very likely to be marine.  But even if we're not talking about your typical Star Trek-style planet with lots of rocks and an orange sky and aliens that look like humans but with rubber facial appendages, the levels of DMS and DMDS suggest a thriving biosphere.

"Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds," said Nikku Madhusudhan of Cambridge University, who co-authored the study, which appeared this week in Astrophysical Journal Letters.  "And now we've observed it, in line with what was predicted. Given everything we know about this planet, a Hycean world with an ocean that is teeming with life is the scenario that best fits the data we have."

The issue, of course, is not just the statistical significance; 99.7% seems pretty good to me, even if it doesn't satisfy the scientists.  The problem is that sneaky little phrase that was in my description of biosignatures earlier; "as far as we know."  We don't know of a way to produce DMS and DMDS in significant quantities except by biological processes, but that doesn't mean one doesn't exist.  It could be that in the weird chemical soup on an planet in another star system, there's an abiotic way to produce a stable amount of these two compounds, and we just haven't figured it out yet.

Be that as it may, it's still pretty damn exciting.  It's certainly the closest we've gotten to "there's life out there."  And being only 124 light years away -- in our stellar neighborhood, really -- it's right there for us to study more intensively.  Which the astronomers will definitely be doing.

So that's our cool news for today.  I don't know about you, but now I'm daydreaming about what kind of life there might be on a world entirely covered by water.  I'm sure that whatever they are, they'll be "forms most beautiful and most wonderful" beyond Charles Darwin's wildest dreams.

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Hotspot

Today's topic in Skeptophilia isn't controversial so much as it is amazing.  And shows us once again what a weird, endlessly fascinating universe we live in.

First, though, a bit of a science lesson.

A great many processes in the natural world happen because of the Second Law of Thermodynamics.  The Second Law can be framed in a variety of ways, two of which are: (1) heat always tends to flow from a hotter object to a colder one; and (2) in a closed system, entropy -- disorder -- always increases.  (Why those are two ways of representing the same underlying physical law is subtle, and beyond the scope of this post.)

In any case, the Second Law is the driver behind weather.  Just about all weather happens because of heat energy redistribution -- the Sun warms the ground, which heats the air.  Hot air tends to rise, so it does, drawing in air from the sides and creating a low pressure center (and wind).  As the warm air rises, it cools (heat flowing away from the warmer blob of air), making water vapor condense -- which is why low pressure tends to mean precipitation.  Condensation releases heat energy, which also wants to flow toward where it's cooler, cooling the blob of air further (which is also cooling because it's rising and expanding).  When the air cools enough, it sinks, forming a high pressure center -- and on and on.  (Circular air movement of this type -- what are called convection cells -- can be local or global in reach.  Honestly, a hurricane is just a giant low-pressure convector.  A heat pump, in essence.  Just a fast and powerful one.)

Okay, so that's the general idea, and to any physicists who read this, I'm sorry for the oversimplifications (but if I've made any outright errors, let me know so I can fix them; there's enough nonsense out there based in misunderstandings of the Second Law that the last thing I want is to add to it).  Any time you have uneven heating, there's going to be a flow of heat energy from one place to the other, whether through convection, conduction, or radiation.

But if you think we get some violent effects from this process here on Earth, wait till you hear about KELT-9b.

KELT-9b is an exoplanet about 670 light years from Earth.  But it has some characteristics that would put it at the top of the list of "weirdest planets ever discovered."  Here are a few:

• It's three times the mass of Jupiter, the largest planet in our Solar System.
• It's moving at a fantastic speed, orbiting its star in only a day and a half.
• It's tidally locked -- the same side of the planet is always facing the star, meaning there's a permanently light side and a permanently dark side.
• It's the hottest exoplanet yet discovered -- the light side has a mean temperature of 4,300 C, which is hotter than some stars.

So the conditions on this planet are pretty extreme.  But as I found out in a paper by Megan Mansfield of the University of Chicago et al. in Astrophysical Journal Letters, even knowing all that didn't stop it from harboring a few more surprises.

Artist's conception of KELT-9b [Image is in the Public Domain courtesy of NASA/JPL]

Tidally-locked planets are likely to have some of the most extraordinary weather in the universe, again because of effects of the Second Law.  Here on Earth, with a planet that rotates once a day, the land surface has an opportunity to heat up and cool down regularly, giving the heat redistribution effects of the Second Law less to work with.  On KELT-9b, though, the same side of the planet gets cooked constantly, so not only is it really freakin' hot, there's way more of a temperature differential between the light side and the dark side than you'd ever get in our Solar System (even Mercury doesn't have that great a difference).

So there must be a phenomenal amount of convection taking place, with the atmosphere on the light side convecting toward the dark side like no hurricane we've ever seen.  But that's where Mansfield et al. realized something was amiss.  Because to account for the temperature distribution they were seeing on KELT-9b, there would have to be wind...

... moving at 150,000 miles per hour.

That seemed physically impossible, so there had to be some other process moving heat around besides simple convection.  The researchers found out what it is -- the heat energy on the light side is sufficient to tear apart hydrogen molecules.

At Earth temperatures, hydrogen exists as a diatomic molecule (H2).  But at KELT-9b's temperatures, the energy tears the molecules into monoatomic hydrogen, storing that as potential energy that is then rereleased when the atoms come back together on the dark side.  So once again we're talking the Second Law -- heat flowing toward the cooler object -- but the carrier of that heat energy isn't just warm air or warm water, but molecules that have been physically torn to shreds.

So, fascinating as it is, KELT-9b would not be the place for Captain Picard to take his away team.  But observed from a distance, it must be spectacular -- glowing blue-white from its own heat, whirling around its host star so fast its year is one and a half of our days, one side in perpetual darkness.  All of which goes to show how prescient William Shakespeare was when he wrote, "There are more things in heaven and Earth, Horatio, than are dreamt of in your 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), which is why my wife and I notice the difference in our hot tub when it's set at 100 F rather than 102 F.  A two-degree temperature difference in air temperature, you'd hardly register; two degrees' difference in water represents a lot of extra heat energy.

There's also the huge heat of vaporization (the heat energy required for it to evaporate), which is why sweating cools you down so efficiently.  Both the high specific heat and high heat of vaporization contribute not only to allowing our body temperature easier to regulate, they make climates near bodies of water warmer in winter and cooler in summer than it otherwise would be.  Other odd properties of water include its cohesiveness, 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.  Finally, 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 a team led 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 bizarre fluid has a density about a third that of liquid water at room temperature, so way more dense than your typical gas but 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.  (Compare that to the Earth, which is about 0.02% water by mass.)

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 Adelaide Brooke and her ill-fated crew had to contend with.

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Puff piece

A couple of posts ago I mentioned how there have been discoveries of exoplanetary systems that have challenged our understanding of how planets form -- including planets with wildly misaligned orbits and the phenomenon of "hot Jupiters," gas giants close enough to their parent stars that you'd expect (based on what we understand of the physics) they would have their lightweight, hydrogen-rich atmospheres blown clean away.

Yesterday I ran into some new research showing that the latter phenomenon -- low-density atmospheres being oddly resistant to annihilation -- is a problem with another kind of exoplanet, which are called (I shit you not) "super puff planets."  They are not, I hasten to point out, where these characters come from:

Although admittedly, those three do look like aliens to me.  I mean, what's with the ginormous eyes, and the fact that they appear not to have noses or fingers?  And apparently they can fly, although I only know this by inference from the still-shots, as I have never watched the show (and have no intention of doing so).  A few years ago I was maneuvered by a friend into watching a forty-five second clip from My Little Pony, and that did enough psychological damage that I'm wary of walking into the same danger again.

But I digress.

"Super puff planets" aren't fiction at all; they are planets with an extraordinarily low density.  The lowest-density planet in our own Solar System is Saturn, which at an average of 0.69 g/cm^3 is light enough that it would float in water (if you could find a pool big enough).  But super puff planets beat Saturn by a mile; they have an average density of 0.05 g/cm^3, which is about the same as cotton candy.

The open question, of course, is not only how they don't get blown apart by the light, heat, and stellar wind from their parent stars, but what allows them to form in the first place.  Planets are held together because they're massive enough that their gravitational energy overcomes other forces (like electrostatic repulsion) that might act to fragment them.  This is why planets are all roughly spherical; it's the equilibrium shape for something that is gravitationally bound -- and the heavier they are (like the neutron stars that were the subject of my post a couple of days ago), the rounder they are.  Small bodies, like the asteroids and some of the smaller moons of the planets in our Solar System, can be some other shape; massive bodies are pulled into spheres.

So how super puff planets (1) form, and (2) don't get immediately torn to shreds, is still unknown.  Which makes it even wilder that a paper this week in The Astronomical Journal describes a system, Kepler 51, that has three -- perhaps four -- of these cotton-candy planets.

"Super puff planets are very unusual in that they have very low mass and low density," said Jessica Libby-Roberts, Center for Exoplanets and Habitable Worlds Postdoctoral Fellow at Penn State, and co-first author of the paper.  "The three previously known planets that orbit the star, Kepler-51, are about the size of Saturn but only a few times the mass of Earth...  We think they have tiny cores and huge atmospheres of hydrogen of helium, but how these strange planets formed and how their atmospheres haven't been blown away by the intense radiation of their young star has remained a mystery.  We planned to use JWST to study one of these planets to help answer these questions, but now we have to explain a fourth low-mass planet in the system!"

Explanations, thus far, have proven elusive.  Right now, super puffs and hot Jupiters are both mysteries, planets that somehow form and maintain a thick atmosphere when by everything we know of astrophysics, they should be more like airless, rocky, superheated Mercury.  It does raise one hopeful thought, however; one of the "Goldilocks zone" qualifications for planetary habitability is that the planet in question needs to resist having its atmosphere blown away by the stellar wind of the parent star.  M-type red dwarf stars, for example, by far the most common stars in the galaxy (they make up an estimated seventy percent of the stars in the Milky Way), have been thought by some to be ruled out as habitable systems on that basis.  First, being low-temperature, any planets warm enough to have liquid water would have to be in close orbits; and second, those close orbits would make the planet a target for stellar storms, potentially destroying any atmosphere the planet had.

This may need to be rethought.  Atmospheres, as it turn out, may be a great deal more durable than we'd reckoned.

So there's yet another odd and unexplained phenomenon from the skies.  Planets as light as cotton candy.  Shakespeare knew whereof he spoke when he wrote, "There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."

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Out of line

Astrophysicists have a fairly clear idea about how planetary systems form.

The whole thing starts with a nebula -- a cloud of interstellar gas and dust,  mostly made of hydrogen and helium -- that begins to contract under the influence of gravity.  Assuming it's large enough, that compaction raises its temperature; and because almost always, the cloud as a whole had some angular momentum to start with (i.e. it had a net spin around the nebula's center of mass, even if a small one) its rotational rate increases as the collapse proceeds.  That increase in spin rate flattens the cloud out -- think of a whirling blob of pizza dough in the hands of someone who knows how to make the perfect pizza crust -- resulting in a concentrated mass in the center (the future star) and a "protoplanetary disk."

The disk is never perfectly uniform, so the higher gravitational pull of the denser parts draws in more material, making them denser still -- a classic example of positive feedback.  Those lumpy bits form the planets, ultimately gaining sufficient mass to gravitationally clear the regions around their orbits.  When the star becomes dense and hot enough to initiate fusion, the light and heat blow away lighter elements (hydrogen and helium), leaving the inner regions enriched in heavier elements like carbon, silicon, magnesium, nickel, aluminum, and iron.

This model explains two things; why the planets in the Solar System all have relatively circular orbits that are aligned with each other and with the spin plane of the Sun, and why the inner planets (Mercury, Venus, Earth, and Mars) are dense and rocky, while the outer ones (Jupiter, Saturn, Uranus, and Neptune) are gas giants.

But.

When we get too confident, nature has this awkward way of saying, "You think you understand everything?  Ha.  A lot you know."  Back in the 1990s people looking for exoplanets started finding what are now nicknamed "hot Jupiters," which are gas giants locked in a tight orbit around their host stars.  Hot Jupiters seem to be pretty common; on the other hand, it may just be that they're simple to spot.  Given their size and mass, they are going to be easier to pick up both by the transit method (the dip in a star's brightness as its planet crosses in front of it) and the wobble method (stars having a slight back-and-forth "wobble" as the star and its planet orbit their common center of gravity; this effect is more pronounced for larger exoplanets and ones with closer orbits).  

So how does a gas giant form, and remain stable, so near to its host star?  Wouldn't the light and heat of the star blow away the lightweight gases, as they seem to have done in our own Solar System?

The answer is "we're not sure."

Another spanner in the works comes from planets that are misaligned -- that have rotational axes or orbital planes skewed with respect to the rotational plane of the star.  There are two examples in our own Solar System; Venus (which actually rotates backwards as compared to the other planets; its day is longer than its year) and Uranus (which lies on its side -- its rotational axis is tilted 82 degrees with respect to its orbital plane).

Neither of these has been explained, either.

But weirdest of all is when a planet's orbital plane is out of alignment with both the star's rotation and the orbits of other planets in the system.  This, in fact, is why the topic comes up; a paper this week in the journal Astrophysics presents some strange new data on the system AU Microscopii, suggesting that the planet AU Microscopii c has its orbital plane tilted by 67 degrees with respect to everything else in the system.  So as the other two planets, and the star itself, are all moving in a nicely aligned fashion, AU Microscopii c is describing these wild loops above and below the system's orbital plane.

You might be wondering how they figured out the orientation of the rotational axis of the star, since most stars look like points of light even in large telescopes.  And this part is really cool.  It's called the Rossiter-McLaughlin effect.  As a star rotates, from our perspective half of the star's disk is heading toward us while the other half is heading away.  So the light from the part that's coming toward us gets slightly blue-shifted, and the light from the other half is simultaneously red-shifted.  Now, imagine a large planet crossing in front of the star, orbiting in the same direction as the star is rotating.  First the blue-shifted part of the light will be partially blocked, then the red-shifted part, resulting in a spectrum alteration that will look like this:

[Image licensed under the Creative Commons Amitchell125, Animation of the Rossiter-Mclaughlin (RM) effect, CC BY-SA 4.0]

So we know the rotational plane of the star from the Rossiter-McLaughlin effect, and the orbital planes of the planets from the direction of the star's wobble.

And they don't line up.  At all.

This completely confounds our models of how planetary systems form.  Did a close pass by another heavy object yank one of the planets out of alignment?  Or an actual collision with something?  (That's one guess about why Uranus's axis is tilted.)  The answer is still "we don't know."  What seems certain is that the configuration is gravitationally unstable.  AU Microscopii is thought to be a young star, on the order of 24 million years old; the Solar System is over five hundred times older than that.  As I described in a post a couple of years ago, long-term stability usually requires some kind of orbital resonance, where the gravitational pull of planets acts to reinforce their trajectories, keeping them all locked in a tight celestial dance.  So it seems like the weird loop-the-loop described by AU Microscopii c is unlikely to last long.

But it's also an orbit that, based on what we know, shouldn't have happened in the first place.  So maybe it's not a good idea to place bets on what it's going to do in the future.

In any case, it's yet another example of how far we have to go in our understanding of the universe we live in.  That's okay, of course; it'd be boring if we had it all figured out.  Science is like some benevolent version of the Hydra from Greek mythology; for every one question we answer, we create nine more.

I think the scientists are going to be busy for a very long time to come.

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In the dark

Dear Readers:

After today's post, I'm going to be taking a long-overdue break from Skeptophilia.  My intent -- lord willin' an' the creek don't rise, as my grandma used to say -- is that my next post will be Monday, May 13.  See you then!

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To further investigate our general topic of people giving woo-woo explanations to damn near everything, today we investigate: The Dark.

First, a brief physics lesson.

Things are generally called "dark" for one of two reasons.  First, there are objects whose chemical makeup results in their absorbing most of the light that falls on them.  Second, there are things that don't interact with light much at all, so they neither absorb nor reflect light -- light passes right through them.  An example of the first would be a charcoal briquet.  An example of the second would be interstellar space, which is sort of dark-by-default.

This whole thing comes up because of an extrasolar planet with the mellifluous name TrES-2b.  TrES-2b orbits the even more charmingly named GSC 03549-02811, a star about 718 light years away.  More interestingly, it has the distinction of being the darkest extrasolar planet yet discovered.  David Kipping, of the Harvard-Smithsonian Center for Astrophysics, stated, "TrES-2b is considerably less reflective than black acrylic paint, so it is truly an alien world."

Artist's conception of TrES-2b  [Image is in the Public Domain courtesy of NASA/JPL-Caltech]

That was all it took.  Whereas my reaction was, "Huh!  A Jupiter-sized charcoal briquet!  That's kinda cool," the woo-woos just couldn't resist wooing all over this story.  We now have the following speculations, all from websites owned by people who probably shouldn't be allowed outside unsupervised:

• TrES-2b is made of antimatter, and we shouldn't go there because it (and we) would blow up.  We know it's antimatter because antimatter has the opposite properties to matter, so it's dark.
• TrES-2b is made of "dark matter," and yes, they're not just talking about stuff that's black, they're talking about the physicists' "dark matter," about which I'll have more to say in a moment.
• TrES-2b is dark because it's being hidden by aliens who are currently on their way to Earth to take over.  Lucky for us we spotted it in time!
• TrES-2b is hell.  No, I'm not making this up.

Well.  You just opened the floodgates, now didn't you, Dr. Kipping?

The first two explanations left me with a giant bruise on my forehead from doing a faceplant while reading.  At the risk of insulting my readers' intelligence, let me just say quickly that (1) antimatter's "opposite properties" have nothing to do with regular matter being light and antimatter being dark, because if it did, the next time a kindergartner pulled a black crayon out of the box, he would explode in a burst of gamma rays; and (2) "dark matter" is called "dark" because of the second reason, that it doesn't interact with much of anything, including light, so the idea of a planet made of it is a little ridiculous, and in any case physicists haven't even proved that it exists, so if some astrophysicist found a whole freakin' planet made of it it would KIND OF MAKE HEADLINES ALL OVER THE FUCKING WORLD, YOU KNOW?

*brief pause to do some nice, slow deep breathing*

Sorry for getting carried away, there.  But I will reiterate something I have said more than once, in this blog; if you're going to start blathering on about science, for cryin' in the sink at least get the science right.  Even the least scientific woo-woo out there can read the Wikipedia page for "Dark Matter," for example, wherein we find in the first paragraph the sentence, "The name refers to the fact that it does not emit or interact with electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum." (Italics mine, and put in so that any of the aforementioned woo-woos who are reading this post will focus on the important part.)

And I won't even address the "secret alien base" and "hell" theories regarding TrES-2b, except to say that it should come as a relief that the evil aliens or Satan (depending on which version you went for) are safely 718 light years away.  To put this in perspective, this means that if they were heading here in the fastest spacecraft humans have ever created, Voyager 1, which travels at about 16 kilometers per second, it would still take them eleven million years to get here.

In any case, I guess it's all a matter of how you view what's around you.  I find the universe, and therefore science, endlessly fascinating, because what scientists have uncovered is weird, wonderful, and counterintuitive.  I don't need to start attaching all sorts of anti-scientific bunk to their discoveries -- nature is cool enough as it is.

Okay, thus endeth today's rant.  I will simply end with an admonishment to be careful next time you barbecue.  I hear those charcoal briquets can be made of antimatter, which could make your next cook-out a dicey affair.  You might want to wear gloves while you handle them.  Better safe than sorry!

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Locked in place

The Moon orbits the Earth in such a way that the same side always faces us.  Put another way, its periods of revolution and rotation are the same; it takes the same amount of time for the Moon to turn once on its axis as it does to circle the Earth.

This seems like a hell of a coincidence, but there is (of course) a physical explanation for it.  Close orbits -- either of a planet around its host star, or a satellite around a planet -- generate a high tidal force, which is the gradient in the gravitational force experienced by the near side of the orbiting body as compared to the far side.  There's always going to be a tidal force; even tiny Pluto has a greater pull from the Sun on the near side than it does on the far side, but with a small body at that great a distance, the difference is minuscule.  (You're experiencing a tidal force right now; the Earth is pulling harder on your feet than on your head, assuming you're not upside down as you're reading this.)  But the Moon's proximity to the Earth means that the tidal force it experiences is comparatively huge.  So even if it once rotated faster than it revolved, the higher pull on the near side slowed its rotation down -- a sort of gravitational drag -- until the two matched exactly.

The result is called 1:1 tidal locking, and is why (apologies to Pink Floyd) there is no permanently dark side of the Moon.  There's a near-Earth and a far-Earth side, but no matter where you are on the Moon, you'll have a 28-day light/dark cycle.  However, the apparent position of the Earth in the sky doesn't change.  If where you stand on the Moon's surface, the Earth appears to be hovering thirty degrees above the western horizon, that's where it will always be from that perspective.

It's been known for some time that planets can also be tidally locked.  Once again, it's more likely to happen when they orbit close to their host star, which means a lot of tidally-locked planets are probably so hot they're uninhabitable.  But the situation changes if the host star is a red dwarf -- small, low-luminosity stars that are incredibly common, making up almost three-quarters of the stars in the Milky Way.  These stars have such a low heat output that the "Goldilocks zone" -- the distance from the star in which the conditions are "just right" for liquid water to form -- is very close in.

So a star in a red dwarf's habitable zone might well also be tidally locked.

Think of how bizarre a situation that would be.  If the planet is at the right distance for the lit side to be comfortable, there'd be a region of perpetual twilight bounding it, and on the other side of that, permanent, freezing-cold night.  Not only that; this would create the convection cell from hell.  Weather down here on Earth is largely caused by uneven heating of the planet's surface; air warms and rises near the Equator, cools, eventually becoming cool enough to sink and completing the circle.  The Earth's rotation and topography complicate the situation, but basically, that convective rise-and-fall is what generates wind, clouds, rain, snow, and the rest of the meteorological picture.

On a tidally-locked planet, these processes would be almost certainly be amplified beyond anything we ever see on Earth.  Especially the twilit boundary zone -- the constant heating of the bright side, and loss of heat to radiation on the dark side, would cause the atmosphere on the bright side to rise, drawing in cold air from the dark side fast.  The result would be a screaming hurricane across the boundary.

At least, so we think.  We don't have any tidally-locked planets to study, only airless moons.

Until now.

A study out of McGill University has confirmed the first tidally-locked exoplanet, LHS 3844b, a "super-Earth" that was identified by measuring the light coming off the planet at different places in its orbit -- something that allowed the researchers to estimate its temperature.

Artist's impression of the dark side of LHS 3844b [Image credit: NASA/JPL-Caltech/R. Hurt (IPAC)]

Chances are, LHS 3844b doesn't have much of an atmosphere, so the convective hellscape I described above might not apply to it.  Still, the idea that astronomers have identified that an exoplanet is tidally locked is kind of astonishing.  The first exoplanet was only discovered in 1992; in the intervening thirty-odd years not only have we found thousands of them, we're now getting so good at analyzing them we can figure out the size of their orbits, how fast they rotate, and the probable composition of their atmospheres.

Our understanding of the universe has accelerated so much, it's hard even to imagine where it might be headed.  The idea that we could not only find an exoplanet around a distant star, but determine that the same side of the planet always faces the star, boggles the mind.

The future of astronomy is looking pretty stellar, isn't it?

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