Sciency Words: The YORP Effect

Hello, friends!  Welcome to another episode of Sciency Words, a special series here on Planet Pailly where we talk about the definitions and etymologies of scientific terms.  In today’s episode, we’re talking about:


Picture a windmill.  As the wind gets stronger or weaker, the windmill spins faster or slower, right?  Okay.  Now replace the windmill with an asteroid orbiting the Sun, and replace the wind with sunlight.  Over long periods of time, sunlight can make the asteroid spin faster or slower.  Sunlight can also change an asteroid’s axis of rotation.  This is known as the YORP Effect (not to be confused with the Yarkovsky Effect).

Definition of the YORP Effect: In astrophysics, the YORP effect is what happens when reflected and/or absorbed sunlight generates “thermal torque” on an asteroid.  Reflected sunlight exerts a very small (but non-zero) amount of force on the surface of an asteroid.  Absorbed sunlight radiates away from the surface of an asteroid as heat, exerting an additional small (but non-zero) amount of force.  Due to the irregular shapes and material consistencies of asteroids, it’s hard to predict exactly what this thermal torque will do, but over long enough periods of time it can dramatically change an asteroid’s rotation rate and axis of rotation.

Etymology of the YORP Effect: The term was coined in 1999 by American geophysicist David Rubincam.  The YORP Effect, as we currently know it, combines the previous research of Ivan Yarkovsky, John O’Keefe, Vladimir Radzievskii, and Stephen Paddack.  YORP is therefore an acronym of the names Yarkovsky, O’Keefe, Radzievskii, and Paddack.

This all started with Ivan Yarkovsky and his Yarkovsky Effect, which we talked about in last week’s Sciency Words post.  The Yarkovsky Effect has to do with the way sunlight affects the orbital trajectory of an asteroid.  The Yarkovsky Effect was lost to science for a while, then it was reintroduced in 1951.  Shortly after that reintroduction, other scientists started wondering what other effects sunlight might have on an asteroid, which ultimately led to this idea of a thermal torque effect, which we now call the YORP Effect.

To be clear, the Yarkovsky Effect and the YORP Effect are two different effects—one related to an asteroid’s orbital trajectory, the other to an asteroid’s rotation rate and axis of rotation.  They’re caused by the same thing—sunlight—but they are two different effects.

In 2007, observations of an asteroid named 2000 PH5 helped confirm that the YORP Effect is real.  The asteroid had been monitored closely over the course of about four years, and astronomers found that its rotation rate was steadily increasing.  This increase could not be explained by gravitational interactions alone, nor by collisions with other asteroids or any other known effects.  Therefore, by process of elimination, only the YORP effect was left as a possible explanation.  Asteroid 2000 PH5 was subsequently renamed 54509 YORP to honor its help in confirming the YORP Effect.

And in 2013, an asteroid named P/2013 R3 literally YORP-ed itself apart.  The YORP Effect caused the asteroid to spin so fast that it started flinging chunks of itself away.  There may have been some previous collision or other catastrophic event that made P/2013 R3 more fragile; still, in the end, it was the YORP Effect that caused the final destruction of that asteroid.

So if you’re an asteroid flying around in space, be careful.  It may be fun YORP-ing and Yarkovsky-ing around the Solar System, but you don’t want to Yarkovsky yourself into hitting a planet, and you don’t want to YORP yourself into self-disintegration either.


P.S.: The DART Mission is scheduled to crash itself into an asteroid tonight at 7:14 p.m. East Coast time in the U.S. (also known as 23:14 GMT).  If you’re interested, NASA TV will be live streaming the collision on their YouTube Channel.  It would not surprise me if the Yarkovsky and YORP Effects are mentioned as part of NASA TV’s science commentary.

Sciency Words: The Yarkovsky Effect

Hello, friends!  Welcome to another episode of Sciency Words, a special series here on Planet Pailly where we discuss the definitions and etymologies of scientific terms, in order to expand our scientific vocabularies together!  Today’s Sciency Word is:


Imagine an asteroid orbiting the Sun.  Every once in a while, this asteroid passes alarmingly close to Earth.  If you’re familiar with Kepler’s laws of planetary motion, you may expect that scientists could predict, with pinpoint accuracy, where that asteroid will be years, decades, or even centuries into the future.  However, there are certain physical forces acting on asteroids that are not accounted for in Kepler’s laws.  One of those physical forces is known as the Yarkovsky Effect.

Definition of the Yarkovsky Effect: In astrophysics, the Yarkovsky Effect is a thermal force that affects the orbit of asteroids.  Like most planets, asteroids rotate; therefore, you could say that asteroids have day-night cycles.  During daytime, the surface of an asteroid absorbs heat from the Sun.  At night, the asteroid’s surface cools off by radiating heat out into space.  This radiating heat generates a very, very, very small amount of thrust.  Over time, that small amount of thrust can dramatically change the orbital trajectory of an asteroid.

Etymology of the Yarkovsky Effect: The Yarkovsky Effect is named in honor of Polish/Russian civil engineer Ivan Yarkovsky, who first described a similar “heat engine” effect in 1888, and who later published a pamphlet on the topic in 1901.  Yarkovsky’s work would have been lost to history, except that Estonian physicist Ernst Öpik recalled reading Yarkovsky’s 1901 pamphlet and reintroduced the idea to the physics community in 1951.

Yarkovsky was more of a science hobbyist than a professional scientist.  He had a day job working on railroads.  In his free time, he read a lot about science, and he did a lot of thinking.  He performed his own experiments, occasionally, and he came up with some interesting ideas that sound like utter nonsense today, but which must have made sense in the context of late 19th Century science.  Even the Yarkovsky Effect, as Yarkovsky originally described it, was tied up with a now defunct scientific theory called ether theory.

Still, even if his starting assumptions were off track, Yarkovsky stumbled upon the truth at least one time.  Asteroids do have “heat engines,” as Yarkovsky described it.  Asteroids do have these naturally occurring thermal propulsion systems, powered by sunlight, which can mess with their orbits.  The challenge for astrophysicists today is that the Yarkovsky Effect is kind of random (or if it isn’t random, in the truest sense of the word, then it may as well be).

Asteroids are irregularly shaped.  Sometimes, they rotate on more than one axis (I once read a paper that called this multiple axis rotation “chaotic tumbling”).  And in terms of mineral composition, asteroids are made of all sorts of crazy stuff.  Different minerals can absorb and radiate heat in different ways.  So the Yarkovsky Effect pushes asteroids around, but because of all the variables I just mentioned, it’s hard to say which direction the Yarkovsky Effect will push at any given time.  It’s also hard to say how hard of a push the Yarkovsky Effect might give.

Which is why missions to study asteroids—missions like the recent ORISIR-REx Mission or the upcoming DART Mission—are so important.  We may never understand asteroids perfectly, but we do need to understand them better.  There are so many asteroids that fly alarmingly close to Earth.  It would be nice if astrophysicists could predict, with pinpoint accuracy or something near to it, where those asteroids will be years, decades or centuries into the future.


I used the following sources to write this blog post.  The one at the bottom is kind of a long read, but it tells the fascinating story of Ivan Yarkovsky, a man who was nearly forgotten by history.  For those of you who are interested in the history of science, it is well worth a read.

Sciency Words: Stochastic

Hello, friends!  Welcome to another episode of Sciency Words, an ongoing series here on Planet Pailly where we take a closer look at the definitions and etymologies of science or science-related terms.  Today on Sciency Words, we’re talking about:


There are no true synonyms, according to American writer Roy Peter Clark.  Sure, two words may mean basically the same thing.  Two words may be so similar in meaning that you could use them interchangeably.  But there will still be some subtle difference between them, some slight shade of connotation that separates them.  The word “stochastic” is almost a synonym for “random.”  Almost.

Definition of stochastic: In statistics, a stochastic process is a process that is best modeled using a random probability distribution.  The process being modeled may, in fact, be random, or it may not.  The important thing is that a stochastic process is a process that scientists have modeled as if it were random.

Etymology of stochastic: The word comes from an ancient Greek word meaning “to aim in the right direction” or “to guess.”

Lots of things in the world are not truly random, but they may as well be.  The weather.  The economy.  Chemical reactions.  Changes in animal populations.  The orbital drifting of asteroids and comets.  Modeling these things in a strictly deterministic way would be mindbogglingly complicated and utterly impractical.  So scientists create stochastic models instead—models that include some random element to represent the super complicated parts that are impractical to model any other way.

These stochastic models are not perfect, but (as the etymology suggests) they aim us in the right direction, and they allow scientists to make pretty good guesses about what might happen with the weather, or the economy, et cetera, et cetera.


I try to avoid telling you to just go read Wikipedia, but the article about this on Wikipedia is actually pretty good.  Most of the other sources I looked at (or tried to look at) were super math heavy.  And you know how I feel about math.

Sciency Words: Gaganaut

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we take a closer look at the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:


Back in the day, there were only two words for “person who goes to space.”  There were astronauts and there were cosmonauts, with the only meaningful distinction being that astronauts came from the United States and cosmonauts came from the Soviet Union.  Today, multiple space agencies use the word astronaut.  It’s almost (but not quite) a generic term now.  But Russia still uses the word cosmonaut, Chinese astronauts are actually called taikonauts, and just last week I learned that astronauts from India are to be referred to as gaganauts.

Definition of gaganaut: A person from India or otherwise associated with the Indian Space Research Organization (ISRO) who travels to space.

Etymology of gaganaut: Formed by analogy with astronaut and cosmonaut.  The “gaga-” part traces back to a Sanskrit word meaning “the sky,” while “-naut” comes from Greek and means “sailor.”

Aside from national origin, there’s still no real difference between astronauts, cosmonauts, taikonauts, and gaganauts.  They all travel to outer space.  They all do basically the same job.  They all have the same United Nations granted status as “envoys of Mankind” (not that that’s been super relevant yet, but someday… you never know!).

I guess the main takeaway from this is that “astronaut” is not a truly generic term.  It is a term used by most space agencies, but not all of them.  And each of the terms currently in use—astronaut, cosmonaut, taikonaut, and now gaganaut—come with certain cultural and perhaps also political connotations.  Just something to keep in mind whenever we talk about people who go to space, specifically or generically.

The Indian Space Research Organization (ISRO) had originally planned to launch its first crewed mission in December of 2021, according to Wikipedia, but COVID threw a wrench into those plans.  So it will be a few more years before the gaganauts get to fly.

Sciency Words: Flora and Fauna

Hello, friends!  Welcome to another episode of Sciency Words, a special series here on Planet Pailly where we talk about the definitions and etymologies of science or science related terms.  In today’s post, we’re talking about two words:


So this weekend, I was thinking about alien life, as I often do, and it occurred to me that the words “plant” and “animal” are woefully inappropriate words to apply to extraterrestrial organisms.  That got me wondering if maybe the words “flora” and “fauna” would be better.

This is hardly a revolutionary insight.  Arik Kershenbaum talks about this in his book The Zoologist’s Guide to the Galaxy.  You see, in the cosmic sense, when we’re considering life across the entire universe, the words “plant” and “animal” are highly Earth-specific terms.  Strictly speaking, plants are organisms belonging to the kingdom Plantae, and animals are organisms belonging to the kingdom Animalia.  These kingdoms are two branches of the tree of life—Earth’s tree of life.  Not Mars’s tree of life.  Not Proxima b’s tree of life.  Earth’s.

Extraterrestrial life forms would belong to the kingdom… who the heck knows?  I guess astro-taxonomists will have to figure that out if/when extraterrestrial life is discovered.  In the meantime, would it make sense to use the words “flora” and “fauna” as generic terms for plant-like and animal-like aliens?  Initially I thought it would, but after doing some research, I’m not so sure.

Definitions of flora and fauna: In ecology, the words flora and fauna refer to all the plants and animals, respectively, found within a particular ecological region.

Etymologies of flora and fauna: The word “flora” traces back to the Latin word for flower.  Fauna comes from the name of an ancient Roman goddess of fertility.

So the words flora and fauna are not exactly synonyms for plants and animals; however, they do include the words “plants” and “animals” in their definitions.  And extraterrestrials, no matter how plant-like or animal-like they may be, would still have to be categorized as something else.

I still feel like referring to alien life forms as flora and fauna is better than calling them plants and animals.  Or at least it’s less wrong.  But it’s still not perfect.  In a distant, Sci-Fi future, new terminology may need to be invented.


I highly recommend reading The Zoologist’s Guide to the Galaxy by Arik Kershenbaum.  Obviously we do not know at this point what alien life might be like, but, as Kershenbaum argues, we can make some educated guesses based on the way life on Earth does (or does not) work.

Sciency Words: Critical Zone

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we take a closer look at the definitions and etymologies of science or science related terms, in order to expand our scientific vocabularies together.  In today’s post, our Sciency Word is:


So I could make this post about climate change, but I won’t.  Certain people would just get angry with me in the comments, and I’m not in the mood for that today.  So instead, I’m going to talk about Earth’s “critical zone” as something that could be relevant to astrobiological research.

Definition of Critical Zone: In Earth sciences, the critical zone is the surface and near surface environment of our planet—in other words, it’s the part of our planet where life lives.  The proper scientific study of Earth’s critical zone will require an interdisciplinary approach, combining geology, biology, hydrology, and other related fields.

Etymology of Critical Zone: The term was first introduced in 1998 by American sedimentary geologist Gail Ashley.  She called it the critical zone because, in her words, “it’s critical for life” and also because it is “critical to know more about it.”  (Source: see the Eos article in the links below.)

Here’s a fun fact that I like to share at parties: there are somewhere between four and five thousand different minerals found here on Earth.  Four to five thousand!  Other planets in our Solar System are known to have only a few hundred, at best.

Why is Earth so mineralogically diverse?  Plate tectonics, for one thing.  Liquid water plays an important role as well.  Some minerals can only form in the presence of liquid water.  But the biggest factor, by far, is life.  Living things do lots of weird chemistry, and all that weird chemistry messed with the planet’s soil and bedrock. Earth’s biosphere affects Earth’s geology.  And Earth’s geology, in turn, affects Earth’s biosphere.  There’s a synergistic relationship between living things and non-living rocks on this planet—and that is what the concept of Earth’s critical zone is all about.

I feel this is a terribly important concept to understand as it relates to Earth.  It’s also something worth bearing in mind as we think about other worlds out there, worlds which may or may not support life of their own.


I’m going to recommend this article from Eos, entitled “Critical Zone Science Comes of Age.”  I think that article is a pretty good summary of how critical zone research started and how it’s going, and it includes some quotes from Gail Ashley explaining what she was thinking about when she originally coined this term.

I’m also going to recommend this brief article entitled “‘Critical Zones’ on Mars and Across the Solar System,” which attempts to adapt the concept of the critical zone for other worlds.

And if you want to read more about why Earth is so mineralogically diverse, here’s a piece from entitled “Minerals Evolve, Too.”

Sciency Words: Orthogenesis

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we take a closer look at the definitions and etymologies of science or science related terms, in order to expand our scientific vocabularies together.  In today’s post, our Sciency Word is:


Please be advised: orthogenesis is a discredited scientific hypothesis.  It has been for almost a century now.  That being said, the term has been coming up a lot in my research lately, and I do think there’s value in examining scientific hypotheses that didn’t make it, so to speak.  I think looking at a rejected scientific hypothesis, like orthogenesis, can give us a better appreciation for how the scientific method works.

Definition of Orthogenesis: In evolutionary biology, orthogenesis was the hypothesis that life evolves in a straight line progression, from simpler organisms to more complex forms.  Orthogenesis rather strongly implied that evolution is working toward some sort of predetermined end goal (i.e., intelligent life).

Etymology of Orthogenesis: The term was coined in 1893 by German zoologist Wilhelm Haacke, who was not convinced that natural selection alone adequately explained the evolution of complex life on Earth.  The word orthogenesis is derived from two Greek words meaning “straight” and “origin.”

When you think about the history of life on this planet, orthogenesis may seem to make sense.  Life started with just these simple microbes.  Then life “leveled up,” and we got more complex multicellular organisms.  And life kept “leveling up” after that to create fish and trees and dinosaurs and a surprising variety of crabs.  And then came humans, the most “leveled up” of all Earth’s creatures.

But as scientists learned more about genetics, and as they pieced together more of Earth’s fossil record, this straight line progression idea made less and less sense.  Evolution is a messy process.  It works in fits and starts.  It finds of-the-moment solutions without any regard for the future, leaving us with vestigial organs and other biologically inefficient stuff.  Increasing complexity is not necessarily advantageous; sometimes the simpler life forms survive while their more complex cousins go extinct.

By the mid-20th Century, orthogenesis had been soundly rejected by the scientific community.  Natural selection just made more sense in light of all the evidence scientists had accumulated since Wilhelm Haacke’s time.  However, while orthogenesis has not been considered good science for many decades now, certain orthogenetic ideas still linger in popular culture.  Whenever the mad scientist in a Sci-Fi movie starts ranting and raving about the “next phase of human evolution,” that’s orthogenetic talk.  Or when you hear dialogue about how one alien species is “more evolved” than another, that too is orthogenetic talk.

A lot of popular misconceptions about science seem to come from science fiction.  As a Sci-Fi writer myself, this is something I worry about.  “Evolutionary paths” and “evolutionary destiny” are such common tropes; it’s easy to write them into a story without realizing you’ve done it.  But I do not want to make these popular misconceptions about science worse, especially when it comes to a topic as controversial as evolution.


I’m going to recommend this article from on “Goal-Oriented Evolution,” which does a good job summing up how Sci-Fi and other popular media keep getting evolution wrong.

I also highly recommend this research paper entitled “Fossil Horses, Orthogenesis, and Communicating Evolution in Museums,” because orthogenetic ideas don’t only linger on in Sci-Fi.  They’re an ongoing problem in museums, school textbooks, and other educational resources as well.

Sciency Words: Carcinization

Hello, friends!  Welcome back to Sciency Words, a regular series here on Planet Pailly where we talk about the definitions and etymologies of scientific terms.  Today, we’re talking about:


In time, we will all evolve into crabs.  Crabs are the ultimate life form, evolutionarily speaking.  At least that’s what certain Internet memes would have you believe.  But like most Internet memes, this whole “we will all become crabs” idea is an oversimplification of the truth.  Carcinization is a surprisingly common evolutionary process, but it doesn’t happen to all animals in all situations.

Definition of Carcinization: In evolutionary biology, carcinization is the process of evolving a crab-like body structure, especially a crab-like carapace (shell) with the pleon (tail) folded underneath the belly.  A surprising number of animals have evolved to have this body structure independently of one another.

Etymology of Carcinization: The term was coined in 1916 by English zoologist Lancelot Alexander Barradaile.  It uses a Greek root word meaning “crab.”  Although the term carcinization was coined in 1916, scientists had noticed the unusual prevalence of crab-like animals well before that.  Research on this phenomenon can be traced back to the mid-to-late 1800’s.

Carcinization seems to happen a lot in nature, but it does not happen to all animals equally.  It is far, far, far more likely to happen to an animal that already has a few crab-like characteristics.  For example, if you’re a lobster, a shrimp, or a prawn—in other words, if you’ve already got a bunch of legs and a pair of claws, and if you’re already living on the ocean floor—then there may be some real benefits to evolving even more crab-like characteristics.

It’s hypothesized that the compact body shape of a crab (compared to the more elongated shape of a lobster, for example) may make it easier to defend yourself against predators.  A lobster’s pleon (tail) is very exposed; crabs have their pleons neatly tucked beneath their bellies.  The compact body shape of a crab may also make it easier to scuttle about on the ocean floor, which could help crabs evade predators, and crabs may find it easier to fit into tight spaces as a way to hide from predators.

As a science fiction writer, I’ve long wanted to include some crab-like extraterrestrials in my Sci-Fi stories.  All those memes about crabs being the “ultimate life form” led me to believe this would be a good idea.  The actual science behind carcinization makes me think otherwise.  Carcinization certainly happens a lot with certain animals (i.e., crustaceans) living in certain environments (i.e., the ocean floor).  But it’s not a universal principle of evolution.

All that being said, I’m going to put some crab-like extraterrestrials in a story anyway, because I still think it’s still a fun idea.


Here are the research papers I have read or am in the process of reading on the topic of carcinization.  I will have more to say about carcinization later this week.

Sciency Words: Spiritual Bypassing

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we talk about the definitions and etymologies of scientific terms, in order to expand our scientific vocabularies together!  In today’s Sciency Words post, we’re talking about:


I am, first and foremost, a science fiction writer.  That’s why most of the research I share on this blog is so heavily focused on outer space: because most of the stories I write are set in outer space.  But I do a fair amount of psychology research, too, because that helps me write more believable characters.

And right now, I am working on a character who has some personal problems.  He’s experiencing a “crisis of faith,” some might say, but in psychology terms, it may be more accurate to say he’s suffering from spiritual bypassing.

Definition of Spiritual Bypassing: Using spirituality to avoid dealing with your problems, rather than using spirituality to help you cope with your problems or overcome them.

Etymology of Spiritual Bypassing: The term was coined in the 1980’s by Buddhist teacher and psychotherapist John Woodward to describe a pattern of behavior he had observed regularly in his line of work.

I’m so spiritual that I don’t have any faults.  I’m so spiritual that I don’t have any weaknesses.  I’m so spiritual that I don’t need to “work on myself.”  I certainly don’t need to see a therapist.  All my pain and all my problems magically go away, by the grace of God or the Buddha or (insert the name of your favorite Higher Power here).  Any trauma in my past?  Through prayer and/or meditation, I’ve transcended that traumatic experience.  It no longer affects me.  I’m too spiritual to have P.T.S.D., depression, anxiety, or anything like that.

That attitude… that is spiritual bypassing.  It’s avoidance behavior.  It’s not about letting religious or spiritual practices help you grow or change; it’s about using religion and spirituality as an excuse to stay the same.  This may be an effective short term coping mechanism for some, but in the long run your problems (whatever they are, wherever they’re coming from) will catch up with you.

In real life, the line between healthy and unhealthy spirituality is not always so clear cut.  I suspect some people may see spiritual exercises and rituals as a quick fix for whatever emotional issues they may be struggling with.  But even people who live happy, long-term spiritual lives may, from time to time, fall into the trap of spiritual bypassing.  As John Woodward (the man who originally coined this term) described it, spiritual bypassing can be an “occupational hazard” for people who follow the spiritual path.

That is certainly the case for a certain character I’m working on—a person who, in the distant future, becomes an accidental and initially reluctant religious leader.

These are the articles and papers I read while researching this blog post:

Sciency Words: Volatility

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we talk about the definitions and etymologies of science or science-related terms and expand our scientific vocabularies together!  In today’s Sciency Words post, we’re talking about:


Wow, it’s been a while since I did a Sciency Words post.  I’ve really missed writing these things.  Once I decided I was ready to bring this series back to life, I knew right away that volatility was the first word I wanted to cover.  I cannot think of any scientific term that is more frequently misused and misunderstood.

Definition of Volatility: In chemistry, volatility refers to the tendency of a chemical substance to switch from a liquid or solid state to a gaseous state.  The faster a chemical will evaporate or sublimate under ordinary environmental conditions, the more volatile that chemical is said to be.  As examples, alcohol is a highly volatile liquid, and dry ice is a highly volatile solid.

Etymology of Volatility: Words like volatile, volatility, and volatilize trace back to a Latin word meaning “to fly away.”  So you could think of it this way: the individual atoms or molecules of a volatile chemical substance are prone to “flying away” as gas.

Rather strangely for a scientific term, there is no precise mathematical definition or formula for volatility.  It’s not something you can measure, per se, but vapor pressure and boiling points are closely related concepts.  You can measure those things.  If a chemical has a high vapor pressure and/or a low boiling point, you can safely call it a volatile chemical.

As a science fiction writer who does a lot of research about science, I come across the words volatile and volatility a lot.  Most science articles—even articles written for a general audience—do not spell out what these words mean in the context of chemistry.  This can lead to some confusion.

A volatile chemical is not necessarily a dangerous chemical.  In some cases, a chemical that is volatile might also be toxic, corrosive, flammable, or explosive—or it might not.  To say a chemical substance is “volatile” or “highly volatile” simply means that chemical is prone to evaporating or sublimating under fairly ordinary environmental conditions.  That’s all.

Click here for a short article from Chemicool Dictionary titled “Definition of Volatile.”
Or click here for a video from eHow titled “Volatile vs. Non-Volatile in Chemistry.”