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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Goldilocks next door

Springboarding off yesterday's post, about how easy it is to form organic compounds abiotically, today we have: our nearest neighbor might be a decent candidate for the search for extraterrestrial life.

At only 4.24 light years away, Proxima Centauri is the closest star to our own Sun.  It's captured the imagination ever since it was discovered how close it is; if you'll recall, the intrepid Robinson family of Lost in Space was heading toward Alpha Centauri, the brightest star in this triple-star system, which is a little father away (4.37 light years) but still more or less right next door, as these things go.

It was discovered in 2016 that Proxima Centauri has a planet in orbit around it -- and more exciting still, it's only a little larger than Earth (1.17 times Earth's mass, to be precise), and is in the star's "Goldilocks zone," where water can exist in liquid form.  The discovery of this exoplanet (Proxima Centauri b) was followed in 2020 by the discovery of Proxima Centauri c, thought to be a "mini-Neptune" at seven times Earth's mass, so probably not habitable by life as we know it.

And now, a paper in Nature has presented research indicating that Proxima Centauri has a third exoplanet -- somewhere between a quarter and three-quarters of the Earth's mass, and right in the middle of the Goldilocks zone as well.

"It is fascinating to know that our Sun’s nearest stellar neighbor is the host to three small planets," said Elisa Quintana, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who co-authored the paper.  "Their proximity make this a prime system for further study, to understand their nature and how they likely formed."

The newly-discovered planet was detected by observing shifts in the light spectrum emitted by the star as the planet's gravitational field interacted with it -- shifts in wavelength as little as 10 ^-5 ångströms, or one ten-thousandth the diameter of a hydrogen atom.  The device that accomplished this is the Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO -- because you can't have an astronomical device without a clever acronym) at the European Southern Observatory in Cerro Paranal, Chile.  

"It’s showing that the nearest star probably has a very rich planetary system," said co-author Guillem Anglada-Escudé, of the Institute of Space Sciences in Barcelona.  "It always has a little bit of mystique, being the closest one."

What this brings home to me is how incredibly common planets in the Goldilocks zone must be.  It's estimated that around two percent of spectral class F, G, and K stars -- the ones most like the Sun -- have planets in the habitable zone.  If this estimate is accurate -- and if anything, most astrophysicists think it's on the conservative side -- that means there's five hundred million habitable planets in the Milky Way alone.

Of course, "habitable" comes with several caveats.  Average temperature and proximity to the host star isn't the only thing that determines if a place is actually habitable.  Remember, for example, that Venus is technically in the Goldilocks zone, but because of its atmospheric composition it has a surface temperature hot enough to melt lead, and an atmosphere made mostly of carbon dioxide and sulfuric acid.  Being at the right distance to theoretically have liquid water doesn't mean it actually does.  Besides atmospheric composition, other things that could interfere with a planet having a clement climate are the eccentricity of the orbit (high eccentricity would result in wild temperature fluctuations between summer and winter), the planet being tidally locked (the same side always facing the star), and how stable the star itself is.  Some stars are prone to stellar storms that make the ones our Sun has seem like gentle breezes, and would irradiate the surface of any planets orbiting them in such a way as to damage or destroy anything unlucky enough to be exposed.

But still -- come back to the "life as we know it" part.  Yeah, a tidally-locked planet that gets fried by stellar storms would be uninhabitable for us, but perhaps there are life forms that evolved to avoid the dangers.  As I pointed out yesterday, the oxygen we depend on is actually a highly reactive toxin -- we use it to make our cellular respiration reactions highly efficient, but it's also destructive to tissues unless you have ways to mitigate the damage.  (Recall that burning is just rapid oxidation.)  My hunch -- and it is just a hunch -- is that just as we find life even in the most inhospitable places on Earth, it'll be pretty ubiquitous out in space.

After all, remember what we learned from Ian Malcolm in Jurassic Park:

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People made fun of Donald Rumsfeld for his statement that there are "known unknowns" -- things we know we don't know -- but a far larger number of "unknown unknowns," which are all the things we aren't even aware that we don't know.

While he certainly could have phrased it a little more clearly, and understand that I'm not in any way defending Donald Rumsfeld's other actions and statements, he certainly was right in this case.  It's profoundly humbling to find out how much we don't know, even about subjects about which we consider ourselves experts.  One of the most important things we need to do is to keep in mind not only that we might have things wrong, and that additional evidence may completely overturn what we thought we knew -- and more, that there are some things so far out of our ken that we may not even know they exist.

These ideas -- the perimeter of human knowledge, and the importance of being able to learn, relearn, change directions, and accept new information -- are the topic of psychologist Adam Grant's book Think Again: The Power of Knowing What You Don't Know.  In it, he explores not only how we are all riding around with blinders on, but how to take steps toward removing them, starting with not surrounding yourself with an echo chamber of like-minded people who might not even recognize that they have things wrong.  We should hold our own beliefs up to the light of scrutiny.  As Grant puts it, we should approach issues like scientists looking for the truth, not like a campaigning politician trying to convince an audience.

It's a book that challenges us to move past our stance of "clearly I'm right about this" to the more reasoned approach of "let me see if the evidence supports this."  In this era of media spin, fake news, and propaganda, it's a critical message -- and Think Again should be on everyone's to-read list.

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

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!]

Widening the Goldilocks Zone

The oft-quoted line from Jurassic Park, "Life finds a way," got interesting support from an (unrelated) pair of studies that came out this week, which show that life is a great deal more resilient than we realized.

The first, by a team led by Maxwell Lechte of McGill University, resulted in a paper that appeared in Proceedings of the National Academy of Sciences.  Entitled, "Subglacial Meltwater Supported Aerobic Marine Habitats During Snowball Earth," and looked at a curious (and to us, completely inhospitable) time in Earth's history.  Current models support the conclusion that for a significant chunk of time in the Precambrian Period, between 720 and 635 million years ago, the entire surface of the Earth was covered with ice.  Called the "Snowball Earth" period, it's long been a question in evolutionary biology how any living thing could survive this -- the entire land area of the Earth under a sheet of ice, and the ocean cut off from the atmosphere because its surface is frozen solid.

The authors think they've found the answer.  According to their models, subglacial meltwater streaming through stress cracks in the ice would have been sufficient to generate oxygen-rich "oases" in which life could have survive the deep freeze.  The authors write:

The Earth’s most severe ice ages interrupted a crucial interval in eukaryotic evolution with widespread ice coverage during the Cryogenian Period (720 to 635 Ma).  Aerobic eukaryotes must have survived the “Snowball Earth” glaciations, requiring the persistence of oxygenated marine habitats, yet evidence for these environments is lacking.  We examine iron formations within globally distributed Cryogenian glacial successions to reconstruct the redox state of the synglacial oceans. Iron isotope ratios and cerium anomalies from a range of glaciomarine environments reveal pervasive anoxia in the ice-covered oceans but increasing oxidation with proximity to the ice shelf grounding line.  We propose that the outwash of subglacial meltwater supplied oxygen to the synglacial oceans, creating glaciomarine oxygen oases.  The confluence of oxygen-rich meltwater and iron-rich seawater may have provided sufficient energy to sustain chemosynthetic communities.  These processes could have supplied the requisite oxygen and organic carbon source for the survival of early animals and other eukaryotic heterotrophs through these extreme glaciations.

"The evidence suggests that although much of the oceans during the deep freeze would have been uninhabitable due to a lack of oxygen, in areas where the grounded ice sheet begins to float there was a critical supply of oxygenated meltwater," said study lead author Maxwell Lechte in a press release.  "This trend can be explained by what we call a ‘glacial oxygen pump’; air bubbles trapped in the glacial ice are released into the water as it melts, enriching it with oxygen...  The fact that the global freeze occurred before the evolution of complex animals suggests a link between Snowball Earth and animal evolution.  These harsh conditions could have stimulated their diversification into more complex forms."

The second study is of a very peculiar species of bacteria, Metallosphaera sedula, which is from a curious group of microbes called chemolithotrophs -- they "eat rocks" as part of their required metabolism.  Some chemolithotrophs break down minerals like pyrite (iron sulfide), but Metallosphaera is even weirder than that.  It requires minerals -- more specifically, the elements in those minerals -- found in significant quantities only in meteorites.

Metallosphaera sedula  [Image by T. Milojevic et al.]

In "Exploring the Microbial Biotransformation of Extraterrestrial Material on Nanometer Scale," by a team led by Tetyana Milojevic of the University of Vienna, we find out that this bizarre bacteria thrives only with provided with minerals rich with nickel and copper, and in fact was discovered on a stony meteorite called Northwest Africa 1172.

"Meteorite-fitness seems to be more beneficial for this ancient microorganism than a diet on terrestrial mineral sources," said lead author Milojevic in a press release in Science Alert.  "Our investigations validate the ability of M. sedula to perform the biotransformation of meteorite minerals, unravel microbial fingerprints left on meteorite material, and provide the next step towards an understanding of meteorite biogeochemistry."

Besides that, it also brings up a couple of interesting questions -- first, it immediately made me wonder about the largely-ignored idea of panspermia -- that the earliest life on Earth came here from elsewhere in the universe.  The objection has always been that it'd have to be a pretty hardy life form to survive both both the vacuum of interstellar space and the fiery descent and collision of the meteorite with Earth's surface.  The Milojevic et al. study suggests that the first part might be entirely possible -- if the earliest life forms were chemolithotrophs, there's no reason they couldn't have been out there on a piece of space rock, nestled in a crack and chowing down on the minerals.

The other question, though, it the extent to which we're doing the reverse -- bringing terrestrial microbes out into space, contaminating every world we visit.  The conventional wisdom always was that the trip through space would effectively destroy any microorganisms riding on the outside of the spacecraft, but Metallosphaera sedula shows that might be more of an issue than we thought.

In any case, it does show that life is a great deal more resilient than we ever dreamed, further bolstering my contention that it's common out there in the universe.  The so-called "Goldilocks Zone," in which there are Earth-like conditions that foster the generation of life, might be a great deal larger than we ever dreamed.

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Long-time readers of Skeptophilia have probably read enough of my rants about creationism and the other flavors of evolution-denial that they're sick unto death of the subject, but if you're up for one more excursion into this, I have a book that is a must-read.

British evolutionary biologist Richard Dawkins has made a name for himself both as an outspoken atheist and as a champion for the evolutionary model, and it is in this latter capacity that he wrote the brilliant The Greatest Show on Earth.  Here, he presents the evidence for evolution in lucid prose easily accessible to the layperson, and one by one demolishes the "arguments" (if you can dignify them by that name) that you find in places like the infamous Answers in Genesis.

If you're someone who wants more ammunition for your own defense of the topic, or you want to find out why the scientists believe all that stuff about natural selection, or you're a creationist yourself and (to your credit) want to find out what the other side is saying, this book is about the best introduction to the logic of the evolutionary model I've ever read.  My focus in biology was evolution and population genetics, so you'd think all this stuff would be old hat to me, but I found something new to savor on virtually every page.  I cannot recommend this book highly enough!

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

Scanning the skies for life

It will come as no surprise to regular readers of Skeptophilia that one of my dearest wishes is to live long enough to see incontrovertible proof of life on another planet.

Intelligent life would just be the icing on the cake, but I'm not counting on it, especially given how rare it is down here on Earth.  And the best of all -- having the intelligent life come here so I could have a talk with it -- is so unlikely as to be impossible, given the enormous (shall we say astronomical) distances involved.

But that doesn't mean we can't find out more about the conditions that could generate life and the likelihood of it being found elsewhere, as three pieces of research last week showed.

The first, which appeared in the journal Science Advances, is called "The Origin of RNA Precursors on Exoplanets," by a team of Cambridge University astrophysicists, Paul B. Rimmer, Jianfeng Xu, Samantha J. Thompson, Ed Gillen, John D. Sutherland, and Didier Queloz.  In it, we find out that the conditions for forming RNA nucleotides -- the fundamental building blocks of RNA, one of the two carriers of genetic information (and generally thought to be the one that formed first) -- have been narrowed down to a specific range of temperatures and luminance.  The authors write:

Given that the macromolecular building blocks of life were likely produced photochemically in the presence of ultraviolet (UV) light, we identify some general constraints on which stars produce sufficient UV for this photochemistry.  We estimate how much light is needed for the UV photochemistry by experimentally measuring the rate constant for the UV chemistry (“light chemistry”, needed for prebiotic synthesis) versus the rate constants for the biomolecular reactions that happen in the absence of the UV light (“dark chemistry”).  We make these measurements for representative photochemical reactions involving and HS−.  By balancing the rates for the light and dark chemistry, we delineate the “abiogenesis zones” around stars of different stellar types based on whether their UV fluxes are sufficient for building up this macromolecular prebiotic inventory.  We find that the light chemistry is rapid enough to build up the prebiotic inventory for stars hotter than K5 (4400 K).  We show how the abiogenesis zone overlaps with the liquid water habitable zone.  Stars cooler than K5 may also drive the formation of these building blocks if they are very active.

The good news, for exobiology aficionados like myself, is that this not only homes in on what conditions are likely to produce life -- telling us where to look -- they're conditions that are relatively common in the universe.  Which further bolsters something I've said for ages, which is that life will turn out to be plentiful out there.

[Image licensed under the Creative Commons ESO/M. Kornmesser/Nick Risinger (skysurvey.org), Artist impression of the exoplanet 51 Pegasi b, CC BY 4.0]

The second, which appeared in Monthly Notices of the Royal Astronomical Society, suggests one way to detect that life at a distance.  In "Biological Fluorescence Induced by Stellar UV Flares, a New Temporal Biosignature," by Jack T. O'Malley-James and Lisa Kaltenegger (both of Cornell University), we find out that class-M stars -- of which the Sun is one -- not only have the right temperature ranges to foster planets with life, but their habit of generating solar flares could tip us off as to which planets hosted life.  The phenomenon of biofluourescence -- the absorption of high-energy light (such as ultraviolet) and its conversion into lower-energy light (visible light) -- could act as a protective mechanism during solar flares.  So when a star flares up, all we have to do is look for the flash of fluorescence that follows.

"On Earth, there are some undersea coral that use biofluorescence to render the Sun’s harmful ultraviolet radiation into harmless visible wavelengths, creating a beautiful radiance," said study co-author Lisa Kaltenegger, who is the director of the Carl Sagan Institute for Astrophysics.  "Maybe such life forms can exist on other worlds too, leaving us a telltale sign to spot them."

The coolest thing is that one of the stars being studied is Proxima Centauri -- the closest star to our Solar System.  So the technique O'Malley-James and Kaltenegger propose using could find life that is, so to speak, right next door.

As a cool followup to this paper, the following day a paper appeared in arXiv by a team of astrophysicists led by Stefan Dreizler of the Georg-August-Universität Göttingen that found not one but three planets in the "Goldilocks zone" of a relatively nearby star -- GJ1061.  One of the problems with figuring out which planets to study for signs of life is that the mass of the planet and its distance from the star aren't the only factors that matter; another, and one much harder to determine from Earth, is the stability of the orbit.  I still remember when I was a kid watching the generally-abysmal 1960s science fiction show Lost in Space, and was blown away when it was revealed that the planet the Robinson family was on was in a highly elliptical orbit -- so the seasons varied from blisteringly hot at the planet's perigee and freezing cold at its apogee.  (The way it played out in the show was, predictably, kind of silly, but it was a concept I'd never run into before, and at age six I was pretty damned impressed.)

But what Dreizler et al. found was that the three planets around GJ1061 were in stable orbits, meaning it was likely that they were relatively circular.  (Elliptical orbits cross each other and therefore increase the likelihood of collisions or gravitational slingshots slinging a planet into the star or out into space.)

So this gives us another likely candidate for biosignatures.

I'm pretty encouraged at all the effort that's being expended in this endeavor.  I vividly recall watching my favorite movie -- Contact -- for the first time, and being appalled at how astronomer Ellie Arroway had to fight to be taken seriously, not only because she was a woman in what then (and still is to some extent now) was a man's world, but because her area of research was the search for extraterrestrial life.  What more fascinating research is there, to find out if life on Earth is unique -- or if, as I contend, we're just one of a multitude of planets hosting life?

I can't imagine a more deeply resonant idea, nor one that would have as profound an effect on how we see ourselves and our place in the universe.  And if that's not worth researching, I don't know what is.

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This week's Skeptophilia book recommendation is a must-read for anyone interested in astronomy -- Finding Our Place in the Universe by French astrophysicist Hélène Courtois.  Courtois gives us a thrilling tour of the universe on the largest scales, particularly Laniakea, the galactic supercluster to which the Milky Way belongs, and the vast and completely empty void between Laniakea and the next supercluster.  (These voids are so empty that if the Earth were at the middle of one, there would be no astronomical objects near enough or bright enough to see without a powerful telescope, and the night sky would be completely dark.)

Courtois's book is eye-opening and engaging, and (as it was just published this year) brings the reader up to date with the latest information from astronomy.  And it will give you new appreciation when you look up at night -- and realize how little of the universe you're actually seeing.

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

Chasing Goldilocks

Given my fascination with the possibilities of life in other star systems, I was thrilled to read two papers that came out last week detailing our efforts to narrow down where to look.

After all, that's the problem, isn't it?  There are billions of stars in our galaxy alone, and it's impossible to study all of them with any kind of thoroughness.  It seems pretty certain that most stars have some kind of planetary system, but trying to find Earth-like planets is another thing entirely.  Most of the exoplanets that have been identified are gas giants, and a good many of those are very close to their parent star (and so are extremely hot).  The reason these were identified first is not necessarily because they're more common; being more massive, and (for the close-in ones) having a stronger gravitational pull on their stars because of their proximity, makes them easier to see by both of the common methods used -- occlusion (seeing them pass in front of their stars) and Doppler spectroscopy (massive planets cause a wobble in the position of their stars as they orbit).

But there's no reason to believe that Earth-sized planets are uncommon, and indeed, we're now finding that they're plentiful.  The trick, of course, is not only locating one that's the right size, but one in the "Goldilocks zone" -- the distance from the star that is neither too hot nor too cold, but just right.  (Since we're concentrating on "life as we know it, Jim," we're most interested in planets where water can be in liquid form during at least part of its orbit.)

[Image licensed under the Creative Commons ESO/L. Calçada, Artist’s impression of the exoplanet Tau Bootis b, CC BY 4.0]

The first paper, called "Habitable Zones and How to Predict Them," by a team led by Ramses M. Ramirez of the Tokyo Institute of Technology, takes a purely practical approach of not only estimating habitability based upon a planet's size and distance from its star, but looks at composition -- quantity of water, presence of carbonate and silicate minerals, percentage of the atmosphere that is carbon dioxide or methane (both greenhouse gases that considerably raise the heat-trapping ability of the air), and the presence of tectonic activity.  The authors conclude with a cautionary note, however, about not concluding too much based upon partial evidence:

[W]e should be careful about using our Earth to extrapolate about life on other planets, particularly those around other stars.  The future of habitability studies will require first principles approaches where the temporal, spatial, geological, astronomical, atmospheric, and biological aspects of a planet’s evolution are dynamically coupled.  This, together with improved observations, is the key to making more informed assessments.  In turn, only through better observations can we improve such theoretical models.

The second paper, published last week in Astrophysical Journal Letters, describes a study by a team of astronomers from Cornell University, Lehigh University, and Vanderbilt University, in which TESS -- the Transiting Exoplanet Survey Satellite -- will examine 400,000 stars considered good candidates for hosting planets in the habitable zone.

"Life could exist on all sorts of worlds, but the kind we know can support life is our own, so it makes sense to first look for Earth-like planets," said Cornell astronomer Lisa Kaltenegger, who was the study's lead author.  "This catalog is important for TESS because anyone working with the data wants to know around which stars we can find the closest Earth-analogs."

Even the scientists who study this stuff on a daily basis recognize what a leap forward this is.  TESS has already identified over 1,800 stars that have planets up to 1.4 times the mass of the Earth -- considered an upper limit for habitability -- and 408 for which TESS could recognize a planet as small as, or a little smaller than, the Earth from one transit alone.

"I have 408 new favorite stars," Kaltenegger said.  "It is amazing that I don't have to pick just one; I now get to search hundreds of stars."

Unlike the old look-everywhere-and-hope-for-the-best approach, this study starts out by examining the most likely candidates, making the hopes for positive results much stronger.  "We don't know how many planets TESS will find around the hundreds of stars in our catalog or whether they will be habitable," Kaltenegger said, "but the odds are in our favor.  Some studies indicate that there are many rocky planets in the habitable zone of cool stars, like the ones in our catalog.  We're excited to see what worlds we'll find."

So am I.  It's long been my dearest hope to have unequivocal proof of extraterrestrial life in my lifetime.  (Intelligent life would be even better, but I'm trying to keep a modest goal, here.)  The idea that we are now devoting significant time and effort into locating good candidates for hosting life is tremendously exciting.  While it's still not likely that we'll find neighbors to talk to, at least knowing they're out there is cool enough for now.

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This week's Skeptophilia book recommendation combines science with biography and high drama.  It's the story of the discovery of oxygen, through the work of the sometimes friends, sometimes bitter rivals Joseph Priestley and Antoine Lavoisier.   A World on Fire: A Heretic, an Aristocrat, and the Race to Discover Oxygen is a fascinating read, both for the science and for the very different personalities of the two men involved.  Priestley was determined, serious, and a bit of a recluse; Lavoisier a pampered nobleman who was as often making the rounds of the social upper-crust in 18th century Paris as he was in his laboratory.  But despite their differences, their contributions were both essential -- and each of them ended up running afoul of the conventional powers-that-be, with tragic results.

The story of how their combined efforts led to a complete overturning of our understanding of that most ubiquitous of substances -- air -- will keep you engaged until the very last page.

[Note:  If you purchase this book by clicking on the image/link below, part of the proceeds will go to support Skeptophilia!]

Deep life, oxygen, and false positives

In the last couple of days we connoisseurs of all things extraterrestrial received some good news and some bad news.

Let's start with the bad news first.

One of the ways astronomers have suggested we might detect life on other planets is the presence of oxygen in the atmosphere, which could be detected spectroscopically.  Oxygen is highly reactive -- it is, unsurprisingly, a strong oxidizer -- meaning that it will tend to react chemically with whatever's around and get bound up into a compound of some sort.  Therefore, the logic went, if there's oxygen in the atmosphere, something must be releasing it faster than it's being removed by ordinary chemical reactions.

Ergo, a living thing (probably doing some variation on photosynthesis).

A piece of research published this week in Earth and Space Chemistry called, "Gas Phase Chemistry of Cool Exoplanet Atmospheres: Insight from Laboratory Simulations," written by a team of scientists from seven different research institutions, came to a startling conclusion -- that atmospheric oxygen might not be a signature of life but a result of photochemistry (chemical reactions triggered by sunlight).

What the researchers did was to expose various mixtures of gases thought to be common components of exoplanet atmospheres to a variety of temperatures (from 25 C to 370 C) and light intensities and spectra, and they found that in many conditions, the energy from the heat and light was sufficient to break down oxidized gases (such as carbon dioxide) and release molecular oxygen.

"People used to suggest that oxygen and organics being present together indicates life, but we produced them abiotically in multiple simulations," said Chao He of Johns Hopkins University's department of Earth and Planetary Science.  "This suggests that even the co-presence of commonly accepted biosignatures could be a false positive for life."

Now, this doesn't mean that if oxygen is found in an exoplanet's atmosphere, it is a false positive; it's just that the He et al. research shows that the finding would not be the slam-dunk astronomers thought it was.  Which is unfortunate.  Given that it's likely that most of the planets hosting life do not have life forms advanced enough to communicate across interstellar space, it'd be nice to have a way to find out they're out there without leaving Earth.  And one of the better possibilities for that has just been shown to be unreliable.

News from the Deep Carbon Observatory, a project that is the collective effort of over a thousand geologists, chemists, and biologists, is more encouraging.  Most of us have the idea that life is only possible on the thin skin of the Earth, and that if you go very deep into the Earth's crust conditions become quickly hot enough and pressurized enough that nothing could live.

Well, that's not true.

The DCO released research last week showing that the amount of life in the "deep biosphere" might amount to as much as twenty billion tons, meaning it would outweigh all of humanity put together by a factor of twenty.  The DCO team drilled three miles deep into the seafloor, and investigated the deepest gold and diamond mines ever created, and everywhere they looked, they found life.

Lots of it.

They found life flourishing at a temperature of 122 C -- twenty-two degrees above the boiling point of water.  They found it in pitch darkness, where there's nothing around to eat except for rocks.  They found it at crushing pressures in the deepest trenches in the ocean.

Sounds like we might have to redefine what we mean by "conditions hospitable for life."

And, germane to the topic of today's post, it will broaden what conditions lie in the "Goldilocks Zone" -- the region surrounding a star where its planets would experience temperatures that are neither too warm nor too cold, but "just right."  Apparently "just right" has a broader range than we ever dreamed, which means that a great many more planets out there might host life than we ever expected.

However, it bears mention that the denizens of the deep biosphere are all simple.  Nothing much more complex than a nematode (roundworm) has been found down there.  So if you were hoping for running across the Morlocks, so far that's a no.

But it's a pretty exciting finding nonetheless, and supports a contention I've had for years -- that life is common in the universe.  Or, as Ellie Arroway put it in Contact, "If not, it'd be an awful waste of space."  Now it's on the chemists and atmospheric scientists to find us a better way to tell that it's there, since the oxygen idea just got shot down.

We'll see what they come up with.  Because I'm certain that it's only a matter of time before we prove beyond any doubt that we're not alone in the universe.

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This week's Skeptophilia book recommendation is Michio Kaku's The Physics of the Impossible.  Kaku takes a look at the science and technology that is usually considered to be in the realm of science fiction -- things like invisibility cloaks, replicators, matter transporters, faster-than-light travel, medical devices like Star Trek's "tricorders" -- and considers whether they're possible given what we know of scientific law, and if so, what it would take to develop them.  In his signature lucid, humorous style, Kaku differentiates between what's merely a matter of figuring out the technology (such as invisibility) and what's probably impossible in a a real and final sense (such as, sadly, faster-than-light travel).  It's a wonderful excursion into the power of the human imagination -- and the power to make at least some of it happen.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]

Saturday science shorts

Because I am totally disheartened by the news, frustrated by the lack of critical thinking everywhere I look, and also because my blender exploded when I was making breakfast this morning and splattered orange juice and half-processed fruit over every square inch of the kitchen including myself, I am retreating to my happy place, namely: cool stuff in science news.

Let's start with a story from astronomy about something that is a near-obsession with me; the possibility of life on other planets.  This particular research involves the star system TRAPPIST-1, discovered last year and found to have not one, not two, but seven planets, three of which are in the so-called "Goldilocks Zone" (where the temperature is juuuuust right for water to be in liquid form).  Of course, that doesn't guarantee that water's there, just that if it was, it would be liquid, which scientists surmise would be a pretty good indicator of the likelihood of the probability of hosting life.

Now, researchers have found that all of the TRAPPIST-1 planets do have water -- in some cases, up to five percent of their mass.  So the three in the habitable zone might well be water-worlds.  All of which reminds me of the planet Kamino from The Phantom Menace, which otherwise was a dreadful movie, but I have to admit reluctantly that this part was cool.

Here's what we know about the TRAPPIST-1 system, although keep in mind that the illustrations of the planets are artists' renditions of what they might look like:

[image courtesy of NASA/JPL]

So that's pretty wicked cool.  The difficulty, of course, is that even if they did host life, it'd be hard to see that if the inhabitants had not advanced technologically to the point that they were sending out signals.  But even that hurdle might not be insurmountable -- as I wrote in a post a couple of weeks ago, astronomers are now trying to figure out if life is present on an exoplanet by the composition of its atmosphere.

Then, from the realm of biology, we have a study elucidating how those tiny jet fighters of the avian world -- hummingbirds -- maneuver as well as they do.

A group led by Roslyn Dakin and Paolo Segre of the Smithsonian Conservation Biology Institute of Ottawa examined hundreds of hours of high-speed video of hummingbirds in flight, looking at twenty-five different species and examining how they do their amazing aerobatics, including pivoting while in flight, hovering, and moving in an arc so narrow that it almost defies belief.  

The research took them to remote places in Panama, Costa Rica, and my favorite country of Ecuador -- the tiny nation that is host to 250 different species of hummingbirds, including the preternaturally beautiful Violet-tailed Sylph (Aglaiocercus coelestis):

Where I live, we have a paltry one species, albeit a beautiful one -- the Ruby-throated Hummingbird.  So it's no wonder the researchers decided to head south.

Another hummingbird researcher, Christopher Clark of the University of California-Riverside, has said that the new study is like moving from analyzing individual gestures of a ballerina to looking at how the moves fit together.  "Now," Clark says, "we're putting together the entire dance."

Last, some scientists at the University of Zurich have for the first time been able to see new neurons being formed in the brains of embryonic mice.  

Starting out by tagging 63 neural stem cells in the hippocampus, Sebastian Jessberger and his team were able to watch as the neurons grew outward and formed connections (synapses) with neighboring neurons.  What was most intriguing was that some of the new neurons had short lives -- perhaps acting as scaffolding for the developing brain and then self-destructing (undergoing apoptosis) when their task was complete.

Amongst these tagged cells, the red ones are the newest, orange next, and continuing through yellow and green (the oldest cells).

What is most exciting about this is that being mammals, it's expected that the knitting together of the embryonic human brain probably proceeds in a very similar fashion.  So what Jessberger et al. are doing might well inform us regarding how our own neural systems form.

So there you have it -- three cool new developments in the world of science.  Which has cheered me up considerably.  That's a good thing, considering the fact that now I have to go clean my kitchen, which I'm definitely not looking forward to.

Music of the spheres

When I went to graduate school, I think the most surprising thing for me was that we were supposed to think creatively about science.  While I had, for the most part, excelled in my science classes in high school and college, they had mostly required me only to master concepts and then be able to demonstrate my mastery on an exam.  I had never had to synthesize, put ideas together in a novel way, apply concepts from one field in an entirely different one.  Nor had I been expected to critique ideas or arguments; I had merely been expected to understand them.

So my leap into the Graduate School of Oceanography at the University of Washington was a bit of a rude awakening, and was (on the whole) kind of a failure.  I was not, at that point in my life, prepared intellectually for the challenge of applying scientific ideas in a creative way, largely because I'd never had any practice in doing so.

No wonder, then, that I lasted exactly one semester in the School of Oceanography

I have since come to appreciate the role of creativity, lateral "outside of the box" thinking, and pure cleverness in approaching scientific questions.  I still suspect I wouldn't be very good at it -- on the whole, I think it was a good decision to leave the educational track headed toward research -- but at least I understand now that in science, the capacity for creative synthesis is as important as pure knowledge.

I ran into an especially good example of that yesterday, in a field that has always been a source of fascination for me; the study of exoplanets.  There have thus far been over a thousand exoplanets discovered, with new ones being reported all the time.  The most exciting part is when one is found that is in the "Goldilocks Zone" (not too hot, not too cold, juuuuuussst right), where liquid water can exist, and therefore where life is thought to be far more likely.

One of the most exciting planetary systems so far discovered is called "Trappist-1," and is about forty light years from Earth.  Trappist-1 has no less than seven Earth-sized planets, at least a few of which are thought to be in the habitable zone.  But the coolest thing about the Trappist-1 system is that an astrophysicist has explained the relative rates of revolution of the seven planets...

... using principles of harmony in music.

Artist's conception of the Trappist-1 system [image courtesy of the Spitzer Space Telescope and NASA/JPL]

What's funny about this is that famed astronomer Johannes Kepler nearly drove himself insane trying to show that the orbits of the planets in our Solar System were connected somehow to the "five Platonic solids" -- cube, octahedron, tetrahedron, dodecahedron, and icosahedron -- thereby proving that there was some divine order in the heavens rather than (as it appeared) the planets all orbiting at different distances in a seemingly random fashion.  He wrote a book called the Mysterium Cosmographicum (Secret of the Universe) elaborating on this theory.  (Kepler had evidently never heard that Brevity Is The Soul Of Wit, because the full title of his book is 46 words long, which is why everyone just calls it the Mysterium Cosmographicum.)

In any case, Kepler's attempt at forcing the Solar System into a pattern based on the five Platonic solids was a complete flop, and it was only after he abandoned this idea that he made the discovery for which he became famous -- that planets travel in ellipses, not circles, and that regardless of the distance they are from the Sun, their orbits sweep out equal areas in equal times.

In a discovery that would have warmed the cockles of Kepler's heart, a team of astronomers, led by Daniel Tamayo of the University of Toronto-Scarborough, just published a paper last week in Astrophysical Journal Letters suggesting that while the orbits of planets have nothing to do with the five Platonic solids, they do have something to do with the phenomenon of resonance -- when the oscillation of one body influences the oscillation of another.  Tamayo found that the seven planets around Trappist-1 are in stable orbits because they are in a resonance pattern that resembles the relationships between frequencies of notes in a chord.  For example, the second planet in the system completes five orbits in the time taken for the innermost planet to make eight; the fourth planet makes two revolutions every time the third one makes three; and so on.  The combined effect of this is to make the entire system operate in a regular, predictable fashion.

The coolest part of this is that Tamayo turned the periods of revolution for all seven planets into musical notes, with the relationships between the pitches representing the ratios between the period length.  You can hear his recording of the musical representation of the Trappist-1 system at the link above.

You'll be listening to the actual music of the spheres.

"I think Trappist is the most musical system we'll ever discover," said Matt Russo, who is a member of Tamayo's team as well as being a musician, and who designed computer simulations of planetary systems in musical resonance (and ones that were not) to see if they remained stable over time.

Tamayo compared resonance in a planetary system to musicians in an orchestra.  "It's not enough for members merely to keep time," he said.  "Simulating the formation of a system in its birth disk is analogous to an orchestra tuning itself before playing.  When we create these harmonized systems, we find that the majority survive for as long as we run our supercomputer simulations."

So there you have it; a melding of music and astrophysics.  I find myself in awe of this sort of research, mostly because I can't imagine my coming up with an idea this creative myself.  So maybe it's best I decided on teaching and writing as a career.  I may not have much of a facility for connecting disparate concepts myself, but I certainly love to tell others about the delightful research of people who do.