Sciency Words: The Fermi Paradox

March 24, 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:


Enrico Fermi was an Italian physicist, one of the many great scientists who immigrated to the United States right before the outbreak of World War II. He is most noted for creating the first nuclear reactor and the role he played in the development of the atomic bomb.

But that’s not what we’re going to talk about today. Today we’re talking about something Fermi said half-jokingly over lunch.

Where Is Everybody?

Based on some historical detective work, we can say this probably happened in the summer of 1950. Fermi was visiting the Los Alamos National Laboratory. He and a few colleagues were having a lunchtime conversation about flying saucers. Apparently there had been an amusing cartoon about little green men in a recent edition of the New Yorker.

The conversation got serious (sort of) when Fermi suddenly asked: “but where is everybody?” Everyone at the table laughed, but Fermi’s question and the not-entirely-serious discussion that followed would become the basis of what we now call the Fermi paradox.

As a matter of statistics and probability, it seems like advanced alien civilizations should be out there somewhere. There are over 100 billion stars in our galaxy. Many (if not most) of these stars have planets orbiting them. Some of these planets must surely support life, and in at least a few cases intelligent life—life capable of developing interstellar travel.

Even without faster-than-light technology, one or more of these space-faring civilizations could conceivably spread across the whole galaxy in just a few million years. The galaxy is far, far older than that. There’s been plenty of time for the aliens to do it. So where is everybody? Shouldn’t we have heard from somebody by now?

Or so Fermi argued over his club sandwich (or whatever he was eating) in a half-serious conversation about flying saucers. Of course there are plenty of objections to Fermi’s line of reasoning here, but I’m not going to weigh in on that. Not today. I’m saving my opinion for Monday’s post.

Sciency Words: Ultra-Cool Dwarf Star

March 10, 2017

Sciency Words PHYS copy

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 some point, I want to profile each of the planets in the TRAPPIST-1 system one by one for my Exoplanet Explorer series. But it’s too early for that. Right now, we don’t know much about these planets except that they’re there.

But I can say something about TRAPPIST-1 itself. It’s a type of star called an ultra-cool dwarf star.


Apparently TRAPPIST-1 has just barely enough mass to cause hydrogen fusion in its core. That means that for a star, it doesn’t produce a whole lot of energy, and thus its temperature is relatively low. Based on my rough math and statistics I got from Wikipedia, it looks like TRAPPIST-1 is less than half the temperature of our Sun.

This is one of the things that makes TRAPPIST-1 so interesting to me, and why it’s really starting to capture my imagination. It’s not just about all those Earth-like planets. The star itself helps set a lower limit for just how small and cold stars can be.

Sciency Words: Earth Similarity Index

March 3, 2017

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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:


As I’m sure you’ve heard by now, astronomers have discovered seven planets orbiting a nearby star called TRAPPIST-1. Even more exciting, most or all of these new worlds are being described as Earth-like planets. But what does that actually mean?

You’d be surprised by how many “Earth-like” planets/moons we have right here in our own Solar System.

Ag16 Earth-like Worlds

From left to right: Venus, Earth, Mars, and Titan (Saturn’s largest moon).

Earth-like is a rather vaguely defined term. So in 2011, a paper published in the journal Astrobiology attempted to establish an official mathematical system for calculating just how Earth-like an exoplanet is. It’s called the Earth Similarity Index or E.S.I.

Basically, the E.S.I. takes certain characteristics of a planet that can be quantified—such as a planet’s mass, radius, temperature, etc—and compares them to Earth’s. An E.S.I. score of zero indicates a planet that has absolutely nothing in common with Earth, while an E.S.I. of one means the planet is an exact match for Earth… at least with regard to the characteristics being measured and included in our calculations.

Of course even a planet with an E.S.I. of one is not necessarily habitable, so the same Astrobiology paper also proposes a Potential Habitability Index or P.H.I. But that, I think, is a Sciency Word for another day.

P.S.: If you want to dive into the math behind the E.S.I., click here.

Sciency Words: Light Curve

February 24, 2017

It’s been almost a week since I arrived at KIC 8462852, better known as Tabby’s Star, and discovered that the aliens really are building a megastructure. I still have a lot of questions, but the aliens aren’t giving me a lot of answers, and I think it’s time I moved on.

Which brings me to today’s edition of Sciency Words.

Sciency Words MATH

Each week, we take a closer look at some science or science-related term to help us all expand our scientific vocabularies together. Today’s term is:


We met astronomer Bradley Schaefer in Wednesday’s post. Writing for Scientific American, he defines a light curve as “a measure of brightness as a function of time.”

So the light curve of a star with a constant brightness would be a straight line. If you found small, symmetrical dips in that line, that might mean there’s a planet in orbit, especially if the dips appear at regular intervals. Here’s an example of what that looks like, courtesy of NASA.

Other patterns of dips or spikes along a light curve could tell you if you’re looking at a binary star, or a flare star, or a variable star… looking at light curves is a great way to study stars.

As for Tabby’s star, its light curve is apparently a straight line most of the time, aside from tiny fluctuations that typically indicate solar flares and/or sunspots. In other words, Tabby’s star looks normal.

And then abruptly, dips appear in the light curve. Asymmetrical dips, as opposed to the symmetrical dips caused by transiting planets. In some cases, the line doesn’t so much dip as plunge downward, and that means… umm… astronomers do not know what that means.

Any serious discussion about Tabby’s Star should really begin with its weird, almost spastic light curve. I’m choosing to end here, however, because the aliens have made it clear that I’m not welcome.


Now I need to find another megastructure to study, and the best way to do that is to examine the light curves of other stars.

Sciency Words: Tabby’s Star

February 17, 2017

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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:


Something’s wrong with a star named KIC 8462852. It flickers. It dims by as much as 22% for no apparent reason. This is an F-type main-sequence star, meaning it’s only a little bit larger than our Sun. F-type stars shouldn’t behave like this.

KIC 8462852 is sometimes called the WTF Star, because of the paper that first described its abnormal fluctuations in brightness. That paper was subtitled “Where’s the Flux?”

The star is also known (and perhaps better known) as Tabby’s Star, in honor of Tabetha Boyajian, the lead author on that paper.

There are several possible explanations for what might be happening to Tabby’s Star, but it’s the least likely explanation that’s gotten the most hype. Could it be aliens? SETI decided to check it out. They didn’t find anything. But still… it could be aliens.

Massive alien starships might be transiting the star, blocking some of its light. Or perhaps there are enormous space stations orbiting the star. Or maybe we’ve caught an advanced alien civilization in the act of building some kind of megastructure (like a Dyson sphere) completely encircling their sun.

Most professional astronomers do not think it’s aliens. Tabetha Boyajian herself doesn’t seem to take the idea seriously and often jokes about the crazy emails she gets from people who do. And to be perfectly clear, I do not take this alien megastructure hypothesis seriously either.

But just to be sure, I’ve decided to hop into my imaginary spaceship and fly out to KIC 8462852, just so I can see for myself what’s really going on. Wish me luck! I’ll let you know what I find next week.


Sciency Words: Ecotype

December 30, 2016

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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:


Let’s say you discover two groups of antelope. Both groups are the same species, but one group lives on the east side of a mountain range and the other group lives on the west side.

Again, these antelope are all the same species of antelope. But because of a geographic barrier, the two groups rarely if ever intermix or interbreed. As a result, one group has developed thicker wool than the other, or they have slightly different antler shapes, or there’s some other distinctive characteristic that one group has and the other doesn’t.

When you find distinctly different groups within the same species, the groups are called ecotypes. Typically, this sort of differentiation occurs within a species because ecotypes are living in separate ecological habitats.

I first encountered this term in a recent article in Scientific American. As a science terminology enthusiast, I find this to be an interesting kink in the ongoing debate over how to define the word “species”—but the article I read was about something even more interesting than that.

Orca Ecotypes

If we ever learn to communicate with orcas (killer whales), we should tell them about Shakespeare.


Orca ecotypes don’t mix, even though there’s nothing stopping them. They’re genetically compatible. Their territories overlap. They encounter each other in the open ocean all the time, but apparently they don’t like to intermingle due to what Scientific America calls “cultural differences.”

We should be careful about anthropomorphizing animal behaviors. When Scientific American says orcas have “cultural differences,” they mean they have different hunting and feeding practices. And also different clicking/whistling patterns for communication.

Actually, that does sound a little bit like orcas have human-like languages, and maybe even a primitive version of human-like culture. And those linguistic and cultural barriers are enough to keep them apart. We really should tell them about Shakespeare. They’d probably understand a lot of Shakespeare’s themes.

P.S.: You may have missed it, but I was trying to make a West Side Story reference with that thing about antelope.


Life on Mars: The Hunt for Martian Dinosaurs

December 28, 2016

Can Mars support life? Is there anything living on Mars right now? It sometimes seems like Mars is desperately trying to convince us that the answer to both questions is yes.


If you’re hunting for alien life in the Solar System, there are four places you should pay attention to: Mars, Europa, Enceladus, and Titan. Now a thought recently occurred to me—a thought that I’m sure has occurred to other people before: in an astrobiological sense, these four worlds sort of represent the past, present, and future.

  • Mars: a place where alien life might have existed and thrived in the past.
  • Europa and Enceladus: places where life may exist and thrive in the present.
  • Titan: a place where life might start to evolve and thrive sometime in the future (assuming it hasn’t started already).

Regarding Mars, there was clearly a time when rivers, lakes, and oceans of liquid water covered the Martian surface. There’s growing evidence that at least some of the organic chemicals necessary for life were also present. Therefore it’s easy to imagine a time millions or perhaps billions of years ago when Mars had a biosphere as rich and robust as prehistoric Earth’s.

Obviously that robust biosphere is gone now. Even when we hear about the possibility that life still exists on present-day Mars, it’s generally assumed that this life would be only a remnant of what came before. The microbial survivors of whatever wiped out the Martian dinosaurs, so to speak.

Someday (hopefully soon), humans will travel to Mars. When we get there, we may find that all the Martians are long dead. That might seem a bit depressing, but actually I’m kind of excited by the idea that the fossilized remains of Martian dinosaurs might be there, waiting for us to come dig them up.