Sciency Words: Chthonian Planet

September 22, 2017

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


In ancient Greece, there were two ways to pray: with your arms raised up to the gods of Olympus or with your arms lowered in deference to the gods of the underworld, also known as the chthonic or chthonian deities.

Regarding spelling and pronunciation, the “chth” thing makes more sense if you’re familiar with how the Greek alphabet works. Much like the “p” in psychology or the “h” in rhinoceros, the “ch” in chthonian becomes silent in English.

English often retains these silent letters as a way to remind us of a word’s origin and history. Also, we have to do something to keep our spelling bees interesting.

Chthonian became an astronomy term in 2003 thanks to this paper: “Evaporation rate of hot Jupiters and formation of Chthonian planets.” The paper describes a scenario in which a hot Jupiter—a gas giant orbiting waaaaay to close to its parent star—has its entire atmosphere stripped away by solar radiation. Only the planet’s rocky and/or metallic core remains. It would probably look something like this:

This is actually a pretty clever play on the original meaning of chthonian, which could refer to the underworld and all things death-related OR could just mean the earth and everything beneath its surface.

In one sense, chthonian planets are dead. Very, very dead. Also, because a chthonian planet is still located dangerously near to its parent star, conditions there would be truly hellish. But in another sense, these chthonian planets would look like any other Earth-like exoplanets, meaning they are rocky, terrestrial worlds, as opposed to Jupiter or Saturn-like gas giants.

For the time being, the idea of chthonian planets is still more or less theoretical. We have not yet proven definitively that such worlds exist. However, several candidate chthonian planets have been identified. I’ll introduce you to two of them next week.

Sciency Words: Retropy

September 15, 2017

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


In any serious conversation about time travel—and I mean any serious, scientific discussion of time travel, as in the kind of discussion actual real-life physicists might have—there’s a term that is virtually guaranteed to come up: entropy.

I’ve tried to define entropy before for Sciency Words, but I’ve never felt like I’ve done the term justice. It’s a big concept, and kind of a weird concept, and sometimes a depressing concept. It’s also a concept that most of us sort of grasp intuitively, even if we can’t quite put it into words.

The simplest definition is that entropy is the amount of disorder in a system, or perhaps the degree to which a system has decayed. Another good definition is that entropy is the measure of the amount of energy in a system that cannot or can no longer be used for work.

According to the second law of thermodynamics, the total entropy of any closed system will tend to increase over time. You can depend upon that! This makes entropy relevant to time travelers, because it’s one of the very few physical properties that is dependent on which direction time is flowing.

As we move forward in time, entropy will increase. And if entropy is increasing, you (as a time traveler) can be sure that you are traveling forward in time. And if you observe that the entropy of a closed system is decreasing, you can be sure you’re traveling into the past.

In the vocabulary of professional time travelers, there should probably be a special term for when entropy goes into reverse. I don’t know what that word is, but fellow blogger and poet James Ph. Kotsybar (also known as the Bard of Mars) recently proposed a pretty good option: retropy, short for retro-entropy.

He even wrote a haiku about it. It’s worth checking out, along with many of the Martian Bard’s other science-themed poems.

Sciency Words: Angstrom

September 8, 2017

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


Last week on Sciency Words, we talked about spectroscopy, a word that’s so important to the kind of space science I write about here on Planet Pailly that I’m surprised I never covered it before.

But in the interest of brevity, I had to skip a lot of the important parts of the history of spectroscopy. I mentioned Isaac Newton and Niels Bohr, but I completely skipped one of the most important “fathers of modern spectroscopy,” Swedish physicist Anders Jonas Angstrom.

Angstrom is one of those scientists who’s so important he has a unit of measure named after him: the angstrom, which equals 10-10 meters, or 0.1 nanometers, and is represented by the symbol Å (the circle over the A is a Swedish thing—Angstrom’s name is more properly spelled Ångström).

The angstrom is not officially part of the International System of Units (S.I.), but scientists use it anyway. It’s a convenient unit for measuring wavelengths of light, certain tiny crystalline structures, and other distances at the molecular and/or atomic scale.

One of the reasons Anders Angstrom features so prominently in the history of spectroscopy is that he was among the first to combine spectroscopy and photography, allowing him to not only observe a spectrum for himself but to record it for others to see.

In 1868, Angstrom published a book with the first complete map of the Sun’s spectrum in visible light, showing over 1,000 absorption lines indicating the presence of hydrogen, helium, and other elements in the Sun’s atmosphere.

This book, titled Recherches sur le Spectre Solaire (Research on the Solar Spectrum), has long since passed into the public domain, so I was able to find a copy of it available for free online. Now if only I could read French….

As one last note, in his solar spectrum book Angstrom found it convenient to quantify wavelengths of light in units equaling one ten-millionth of a meter, also known as 10-10 meters, or 0.1 nanometers. Or in other words, Anders Angstrom was the first person to measure something in angstroms.

P.S.: I really hope I got my math right for today’s cartoon.

Sciency Words: Spectroscopy

September 2, 2017

Welcome to a special Saturday edition of Sciency Words, because sometimes life gets in the way of regular blogging schedules. Each week (normally on Fridays) we take a closer look at some science or science-related term so we can all expand our scientific vocabularies together! Today’s term is:


What color is it? It sounds almost like a childish question, but as we look out into space, trying to study the Sun and other stars and distant planets, we can learn a great deal just by figuring out what color things are.

The science of spectroscopy has a long history, beginning with Isaac Newton. In the late 1600’s, Newton demonstrated that pure white light can be split apart into a rainbow of color using a prism. Newton called this a spectrum, from the Latin verb specto, meaning “I observe” or “I see.” (According to my trusty Latin-English dictionary, the noun spectrum also meant “apparition” or “ghost.”)

Over the decades and centuries to come (click here for a detailed timeline), scientists used increasingly sophisticated combinations of lenses, mirrors, and prisms to study Newton’s spectrum in greater detail. They also experimented on a wide variety of light sources: sunlight, starlight, firelight, and even electrical sparks.

An especially noteworthy experiment in 1752 showed that burning a mixture of alcohol and sea salt produced an unusually bright yellow band in the middle of the spectrum (we now know this to be a emission line for sodium). And in 1802, another experiment on sunlight revealed multiple dark bands in the Sun’s spectrum (which we now know are absorption lines for hydrogen, helium, and other elements in the Sun’s photosphere and corona).

All the colors of the rainbow, except a few are missing. This is an absorption spectrum.

It wouldn’t be until the early 20th Century, with the development of quantum theory and, specifically, Niels Bohr’s model of the atom, that anyone could explain what caused all these spectral lines.

No rainbow, just a few specific colors. This is an emission spectrum.

In Bohr’s atom, the electrons orbiting an atomic nucleus can only occupy very specific energy levels. When electrons jump from one energy level to another (the true meaning of a quantum leap), they either emit or absorb very specific frequencies of light. The light frequencies are so specific that they act as a sort of atomic fingerprint.

And so today, as we look out into the universe, seeing the glow of stars and the absorption patterns of planetary atmospheres, it’s possible for us to identify the specific chemical elements we’re seeing, even across the vast distances of space, simply by asking what color is it?

Sciency Words: Blackbody Radiation

August 25, 2017

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


This is a thing you already know, even if you don’t know that you know it. In fact this may be one of the very first scientific discoveries you made as a child: when things get really hot, they glow. As they get hotter, they glow brighter and change colors from red to orange to yellow to white.

This concept is modeled scientifically using something called a blackbody. Imagine an object that is perfectly black, by which I mean that it reflects absolutely nothing and absorbs 100% of the light that falls upon it. No such object exists in real life (although vantablack paint comes close), but a good scientist knows how to imagine impossible things for the sake of a thought experiment.

Now if you were to observe this hypothetical perfectly black object in all wavelengths of light, you might find that it glows slightly in infrared. This is due to the blackbody’s internal heat. As the temperature goes up, the “shade” of infrared you see will start creeping towards the visible part of the spectrum.

Soon, the blackbody will glow dull red, then orange, then bright yellow. As the temperature continues to climb, green and blue will get into the mix, but when so many colors of light are mixed together you tend to see pure white. If you keep going, you’ll get into ultraviolet light and beyond.

I have to admit that I’m glossing over a lot of details here (click here or here for a little more technical info). The important thing to know is that under ideal conditions, when you’re dealing with a glowing hot substance or a glowing hot object (like a stovetop or the Sun or flowing lava), color serves as a useful gauge for temperature.

In the late 19th and early 20th Centuries, the study of blackbody radiation became a matter of paramount importance to science, in large part due to the demands of the Industrial Revolution. Industrialists really needed a way to measure the temperatures of things like molten iron or steel. Dipping a thermometer into molten metal wasn’t a practical option.

Scientists came up with ways to approximate blackbodies in real life (it’s really clever how they did this). Thing is in these laboratory experiments the light emitted by blackbodies did not behave the way it was supposed to, according to classical physics.

In 1900, physicist Max Planck came up with what must have felt like an inelegant way to model light’s weird behavior. For Planck’s model to work, he had to pretend light is sometimes a particle and sometimes a wave. That didn’t make any sense, but it worked. Then in 1905, Albert Einstein proved that no pretending was required: light really is both a particle and a wave.

And thus began the madness of quantum physics!

Sciency Words: Brown Dwarf

August 18, 2017

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


In 1962, Indian astronomer Shiv S. Kumar theorized that there could be objects out there in space too big to be considered planets but too small to become stars. Since main sequence stars are referred to as dwarfs of various colors (our own Sun is a yellow dwarf), Kumar called his theoretical objects “black dwarfs.”

It turned out that the term “black dwarf” was already taken, so in 1975 American astronomer Jill Tarter (best known for her work with the SETI Institute) suggested the name “brown dwarf” instead. In an article from Universe Today, Tarter is quoted as saying: “it was obvious that we needed a color to describe these dwarfs that was between red and black.”

The term stuck, despite the fact that “brown” is a very misleading description. It’s not clear to us what color these objects are or would appear to be to the human eye. They do radiate light, but it’s mostly infrared light. In the visible spectrum, they might appear to be purple or magenta, or perhaps a rather dull red or orange. In fact they may come in all sorts of colors, depending on their metallicity. But astronomers do seem to agree about one thing: brown dwarfs are definitely not brown.

Today, brown dwarfs are typically described as failed stars.

Stars are defined scientifically as objects massive enough to cause nuclear fusion in their cores—specifically, to be classified as a star an object must be able to fuse hydrogen into helium. Brown dwarfs can’t do that.

But while this distinction between stars and brown dwarfs is fairly straightforward, the distinction between brown dwarfs and planets can get pretty murky. We actually don’t know enough yet about either brown dwarfs or exoplanets to be sure where to draw the line separating one from the other.

One of the leading proposals would define brown dwarfs based on their formation. If an object coalesces from a molecular cloud, as a star would, but fails to initiate hydrogen fusion, that object would be a brown dwarf. If an object forms in the accretion disk surrounding a star, the way planets form, then that object would not be a brown dwarf.

Another leading proposal would define brown dwarfs based on their internal physics. If an object can’t fuse hydrogen but can fuse other elements like lithium or oxygen, then that object would be a brown dwarf. (For more about these two competing proposals, click here.)

Eventually the International Astronomy Union will have to step in and set an official definition. But they’re not ready to do that. Not yet. Not until we’ve learned a lot more. In the meantime, ongoing observational research of objects like Gliese 504b (which I’ve nicknamed “Pinkie Pie”) may help the I.A.U. figure out which definition makes the most sense.

Sciency Words: Noösphere

August 11, 2017

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


Earth has a lot of “spheres.” There’s the atmosphere, which is the sphere of air surrounding our planet, and the lithosphere, which is the sphere of rock making up our planet’s crust and upper mantel. Earth has a hydrosphere (all of Earth’s surface water) and a biosphere (all of Earth’s organisms, collectively).

Over time, scientists have come to appreciate how all these “spheres” are interconnected with each other, maintaining conditions on this planet that are just right for life. At the risk of sounding New Agey, it’s almost like Earth is alive, like Earth is a single organism, and we’re just small parts of a greater whole. If so, perhaps we can add one more sphere to the list: the noösphere.

The term noösphere (pronounced either new-o-sphere or know-o-sphere) was coined in the 1920’s by a Jesuit priest named Tielhard de Chardin. The word comes from two Greek words: nous, meaning mind, and sphere, meaning sphere. In other words, the noösphere is the sum total of all the knowledge and intelligence on our planet.

Or going back to the New Agey stuff, the noösphere is Earth’s mind. We humans are like cells in Earth’s body, but we’re not just any old cells: we’re Earth’s brain cells. You might even say Earth has started to develop a new level of intelligence, a noösphere 2.0, as all us brain cells form a new series of neural connections with each other (in other words, the Internet is making Earth smarter).

Of course we could push this analogy too far. Are human beings really worthy of being compared to brain cells? Is the Internet really making our planet smarter?

While I’m not ready to declare humanity to be Earth’s brain, I do think the concept of the noösphere is interesting and warrants some discussion. The various spheres of our planet are interconnected, sometimes in weird and surprising ways; so how does the noösphere—the accumulated knowledge and intelligence of all humanity—contribute to (or detract from) the greater whole?

P.S.: I first learned about the noösphere in David Grinspoon’s recent book Earth in Human Hands, which I’ll be reviewing next week.