Sciency Words: Stochastic

June 23, 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:


At first glance, stochastic appears to have a pretty easy definition. Basically, it means random. A stochastic event can be defined, quite simply, as a random event. So why do scientists need this weird term? Why can’t they just say random if they mean random?

I’ve seen this word now in a surprisingly wide range of scientific fields, most recently in relation to the population dynamics of endangered species and then in relation to the magnetic field of Jupiter. The thing is that in actual usage, stochastic and random aren’t quite synonyms. A better definition for stochastic might be “seemingly random.”

The word originates from a Greek word meaning “to aim at” or “to shoot at.” So it’s an archery term, but the Greeks also used it to mean “to guess at.” I like this linguistic metaphor because a guess really is like aiming for the truth; whether or not you hit the mark is another matter.

Anyway, the word seems to have migrated from Greek to German to English, and in its modern scientific sense it refers to something that might be predictable in theory but appears to be random in practice. As an example, you may have heard that the flapping of a butterfly’s wings could set in motion a chain of events ultimately leading to a devastating hurricane.

In theory, these butterfly-initiated hurricanes could be predicted, if only we knew the exact locations and flapping behaviors of every single butterfly on Earth (along with a million and one other factors). But in practice, since we can’t gather all the necessary data, we can only make educated guesses about when and where the next hurricane will hit.

In other words, hurricanes are stochastic events. They seem random, even though they’re not.

What’s the Minimum Viable Population of a Space Colony?

June 21, 2017

Let’s say we’ve found a human-friendly planet orbiting another star, and we’ve decided to go colonize it. How many people should we send? In terms of maintaining a healthy human gene pool, what’s the minimum viable population for a distant, isolated space colony?

If you’re anything like me, you’ve spent many a sleepless night pondering that question.

I sincerely doubt anyone can provide us with a firm, specific number. However, there is a sort of generalized rule of thumb in the field of conservation biology called the 50/500 rule.

Originally proposed in 1980 by geneticist Ian Franklin and biologist Michael Soule, the 50/500 rule tells us:

  • Populations below 50 are under near-term threat of extinction due to inbreeding.
  • Populations below 500 are under long-term threat of extinction because the gene pool is too small to adapt to environmental changes.

Except the 50/500 rule is not a hard scientific law. It’s just a rule of thumb, and it has many, many detractors.

Even Michael Soule, one of the co-creators of the rule, seems to have gotten pretty frustrated by the way people took the rule literally. Here’s an interesting and, I think, revealing article about some endangered parrots. A team of conservationists contacted Soule, asking if they should even bother trying to save these parrots, because there were only 48 left.

There also an argument to be made that the numbers 50 and 500 are too low and that a 100/1000 rule would be more appropriate. And of course, can we really apply this rule to all species equally when some species reproduce more rapidly than others or face different kinds of environmental challenges, etc, etc….

Still, if we’re trying to imagine a colony of humans on some distant world, a colony struggling for short-terma and/or long-term survival, I think the 50/500 rule at least gives us a good place to start.

Sciency Words: Technological Geometrization

June 16, 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 1990, the Galileo spacecraft was on its way to Jupiter and needed to perform a gravity assist maneuver at Earth. This turned out to be a golden opportunity for science. Could a typical NASA space probe equipped with a standard suite of instruments detect signs of life on a planet where we already knew life existed?

In a 1993 paper, Carl Sagan and colleagues presented their findings in this “control experiment for the search for extraterrestrial life.” The paper explores all the things Galileo observed and, more intriguingly, some of the big things Galileo missed. Things like the “technological geometrization” of the planet’s surface, as the paper called it.

As far as I can tell, technological geometrization is not a term that’s stuck in the scientific lexicon, which is a shame. I think it’s a really good term. It refers to the way technologically advanced civilizations would tend to create geometric patterns on their surfaces of their planets.

The planet Coruscant from the Star Wars universe is a great example. The entire planet is urbanized, to the point that natural geological features are completely covered over. From space, all you can see are straight lines and perfect circles—efficient city planning on a global scale.

As another example, back in the 1800’s Percival Lowell and an embarrassingly large number of other astronomers thought they saw canals crisscrossing the surface of Mars. Those canals, if they really existed, would have been clear evidence of a technologically advanced society geometrizing their planet.

Earth’s surface displays only the faint beginnings of technological geometrization: rectangular patches of farmland and the grid patterns of streets and highways. These features are visible from space (Google Earth proves that), but you have to get fairly close to Earth to notice those kinds of details.

Apparently Galileo didn’t get close enough. At an image resolution of 1-2 kilometers per pixel, the technological geometrization of Earth was effectively invisible.

P.S.: That paper by Sagan and Company was a really good paper. It served as the basis for my recent “Alien Eyes on Earth” series.

Have I Been Drawing Enceladus Wrong?

June 13, 2017

Enceladus, one of Saturn’s moons, is becoming increasingly famous as one of those places in the Solar System where we’re most likely to find alien life. It certainly has the water for it. On this blog, I traditionally depict Enceladus like this:

It’s a nice, icy-looking world with a cheerful personality and active geysers in its south polar region. But have I been drawing Enceladus wrong this whole time? Would it make more sense to draw it like this?

Maybe. According to this article from Saturn Daily, Enceladus may have tipped sideways (by about 55°) at some point in its history. Apparently surface features reveal evidence of an old equator and old north and south poles.

The story is that one day, Enceladus was orbiting along, minding its own business, when it got whacked hard by an asteroid. Saturn Daily tells us that following the impact, Enceladus would have spent about a million years wobbling back and forth until it could reorient its rotation.

But Enceladus did manage to reorient itself. It has a new axis of rotation, a new north and south pole, and a new equator. It’s not a sideways moon, at least not anymore, which means by the logic of space cartoons, I’ve been drawing Enceladus correctly.

At least I think I have. What do you think? Does it make sense to draw Enceladus based on its current orientation or its (possible) original orientation?

Sciency Words: Coronal Heating Problem

June 9, 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 the Sun. He’s kind of a big deal, and he knows it.

The interior of the Sun is several million degrees Celsius. By comparison, the surface of the Sun is quite chilly. It’s only a few thousand degrees. Still, if you were standing on the surface of the Sun, you wouldn’t last long.

But before you launch yourself into space to escape the heat, there’s something you should know: as you fly away from the Sun, passing through the corona, the temperature starts getting hotter again. It’s not quite as hot as the interior, but still… we’re back into million-plus degree heat.

If that doesn’t make sense to you, that’s okay. It doesn’t make sense to me either, or anyone else. Astro-scientists have been baffled by this for decades now. They call it the coronal heating problem.

I first heard about the coronal heating problem back in 2014, when I was starting my research for what became the 2015 Mission to the Solar System. To be honest, it’s not something I’ve spent a lot of time thinking about since then. Every once in a while, it comes up again and I think, “Oh right… so they still haven’t figured that out yet?”

But as you may heave heard last week, NASA’s on the case. Their newly named Parker Solar Probe is going to skim very close to the Sun and try to figure out what the heck’s going on.

Parker is scheduled for a launch window in July/August of 2018. Its mission is expected to last until 2025. So hopefully a decade from now, whenever I’m reminded of the coronal heating problem, it won’t be a problem anymore, and I’ll be able to think, “Oh right… they finally figured that out!”

Sciency Words: Biogenic (Alien Eyes on Earth, Part 5)

June 2, 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:


A passing alien spacecraft has been observing our little, blue planet for two weeks now, and it’s time they reported their findings back to their homeworld. One word—one scientific term—will feature prominently in their report: biogenic.

Actually, it’ll be the word xygjaflubozux, but that roughly translates into English as biogenic. It’s an adjective meaning “generated by biological processes.”

It’s difficult to impossible to directly detect life forms on a distant planet, so instead good astro-scientists go looking for chemicals that may have biogenic origins.

In the case of Earth, the aliens report they’ve detected an alarming amount of oxygen in the atmosphere. Oxygen is such a highly reactive chemical that it’s hard to imagine how it could persist in a planet’s atmosphere over long periods of time, unless….

Then there’s methane (which we never talked about in this series… oops). The presence of methane is even harder to explain, because methane reacts so readily with oxygen. All that methane should oxidize away within fifty years, unless….

Could it be biogenic oxygen? Biogenic methane? What about some of the other strange chemicals in Earth’s atmosphere, like nitrous oxide? Could there be biological processes at work constantly replenishing these chemicals in Earth’s atmosphere? These questions will be debated among the alien scientific community for many standard cycles to come.

The only unambiguous evidence of life on Earth, from the aliens’ perspective, were those radio signals coming from the planet’s surface. In a sense, you might say these signals have a biological origin, though I doubt human astro-scientists would describe them as biogenic radio emissions. But maybe the word xugjaflubozux has a slightly broader flavor of meaning and could still apply (how should I know? I don’t speak alien!).

This is the final post for my “Alien Eyes on Earth” series. The aliens have to move on and explore other star systems, but something tells me they’ll be back.

Today’s post was inspired by a 1993 paper by Carl Sagan and others. Sagan and his colleagues wanted to know which of Earth’s features can be observed by a passing spacecraft and, perhaps more interestingly, which features cannot.

Alien Eyes on Earth, Part 4

June 1, 2017

Right now, as you read this, our world is being watched keenly and closely by a nearby alien spacecraft. So far the aliens have only observed circumstantial evidence of life: water, oxygen, and a mysterious light-absorbing chemical (chlorophyll). But the aliens are about to detect something that will prove conclusively not only that there’s life on Earth but that there is intelligent life.

Okay, the content of Earth’s radio broadcasts might not seem all that intelligent, but the existence of such broadcasts is clear, unambiguous evidence of a technologically advanced civilization of some kind.

First off, these radio signals are being affected by Earth’s ionosphere in a particularly telling way. During the day, the ionosphere becomes energized by solar radiation, effectively blocking the planet’s radio emissions from escaping into space. But at night, the ionosphere calms down and allows more radio signals through. Because the aliens detect most of the radio emissions from the night side rather than the day side, it would seem clear to them that the signals originate on the planet’s surface, rather than sources near or directly behind the planet.

Secondly, the radio emissions remain stable at constant frequencies over the course of many hours. Naturally occurring radio emissions would tend to drift significantly from one frequency to another over that time period. This strongly suggests an artificial source.

And thirdly, these signals exhibit “pulse-like amplitude modulation”—in other words, the signals appear to be modulated in such a way as to contain bits of information. I imagine this would present something of a double challenge for the aliens: first the technical challenge of decoding the signals, and then the linguistic challenge of interpreting our language—or rather, our many languages.

Whether or not the aliens could make any sense out of these radio signals, this sort of pulsed amplitude modulation is never observed with naturally occurring radio sources. The only reasonable hypothesis is that there is intelligent life on the planet’s surface.

Tomorrow, in the final post for this “Alien Eyes on Earth” series, the aliens will report their findings back to their home planet, and there’s one word—one particular scientific term—that will feature prominently in that report.

* * *

Today’s post was inspired by a 1993 paper by Carl Sagan and others. Sagan and his colleagues wanted to know which of Earth’s features can be observed by a passing spacecraft and, perhaps more interestingly, which features cannot.

P.S.: Of course the aliens would pick up more than just pop music. They’d be able to hear our news, educational programming, personal cell phone calls, coded military transmissions, et cetera, et cetera… but something tells me that music in particular would draw their interest. The special combination of mathematics and aesthetics is, in my opinion, one of the strongest indicators of intelligent life.