Sciency Words A to Z: Young Surface

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, Y is for:


Imagine a nice, smooth, clean sheet of asphalt: a parking lot, maybe, with no cracks or potholes or blemishes of any kind.  Just looking at it, you would know, with a reasonable degree of certainty, that this asphalt had been laid down recently. It’s new.  It is, in effect, a young surface.

In much the same way, planetary scientists can look at the surface of a planet or moon and infer, with a reasonable degree of certainty, how young or old that surface must be.  Look at the Moon or Mercury; they’re covered in craters, showing that their surfaces must be very, very old.  Or look at Mars, where some regions are more heavily cratered than others, implying (intriguingly) that some surfaces are relatively old and some are relatively young.

And then there’s Europa, one of Jupiter’s moons. Europa may be covered in weird, orangey-red cracks, and it may have a few other orangey-red blemishes, but overall it’s surprisingly smooth, and there are very few craters.  This makes Europa look a whole lot younger than it actually is.  In fact, Europa is said to have the youngest-looking surface in the whole Solar System.

Europa’s surface is made of ice, specifically water ice.  This is not so uncommon for a moon in the outer Solar System.  It’s so cold out there that water behaves like a kind of rock.

But unlike most other icy moons, Europa must be doing something to get rid of old, crater-y surface ice and replace it with new, clean, smooth ice.  And once you really start thinking of water as a kind of rock, you might be able to guess what Europa’s doing.  As stated in this paper from Nature Geoscience: “[…] Europa may be the only Solar System body other than Earth to exhibit a system of plate tectonics.”

Except unlike Earth’s techtonic plates, which float atop a layer of magma (liquid rock), Europa’s plates would be floating atop “magma” that is actually liquid water—twice as much liquid water as we have here on Earth, according to some calculations.

And while liquid water may or may not be necessary for life, we do have good reason to suspect that any place that has liquid water might also have life.  Personally, based on everything else I’ve learned about Europa, I’d be more surprised if we didn’t find something living there.

Next time on Sciency Words A to Z, I have a prediction for the future.

Sciency Words A to Z: SETI

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, S is for:


In September of 1959, Italian physicist Giuseppi Cocconi and American physicist Philip Morrison published this paper, titled “Searching for Interstellar Communications.”  That paper is essentially the founding document for SETI, the search for extraterrestrial intelligence, which is now considered a subfield of astrobiology.

The SETI Institute, on the other hand, was established in 1984 by Thomas Pierson and Jill Tarter.  As stated in this report on the proper use of SETI nomenclature:

SETI should not be used as a shorthand for the SETI Institute, which is an independent entity and should be referred to by its full name to avoid confusion.

And let me tell you, this SETI vs. SETI Institute distinction… that really can cause a lot of confusion.

A few years back, I saw a report on the news.  SETI (the Institute, I presumed) had picked up a signal form outer space, from a star located 94 light years away.  According to the news lady on TV, a SETI spokesperson had this to say, and that to say, and some more stuff to say about this amazing discovery.  “Oh cool,” I thought, and I quickly went to the SETI Institute’s webpage to learn more.

There was nothing—absolutely nothing—about it.

Another day or two went by, and then this article was posted on the SETI Institute’s website.  Some Russian radio astronomers had picked up what they thought was a SETI signal (it eventually turned out to be a satellite).  Somehow the media picked up on this story and ran with it, apparently without contacting the SETI Institute—or speaking with any actual SETI Institute spokesperson—to find out if any of this were true.

I should probably mention that in my day job, I work in the T.V. news business.  This sort of sloppy journalism infuriates me, but I’ve found that it’s quite typical of how the popular press handles science news.

However, to be fair, prior to that misleading news report, I didn’t know to make a clear distinction between SETI and the SETI Institute myself. But I’ve tried to be more careful about this ever since.  Language can be a messy way to communicate, so it’s important to try to be clear about what we mean.  Otherwise, someone (perhaps even someone from the media) will get the wrong idea and run with it.

Next time on Sciency Words A to Z, the first astronauts on Titan may find themselves in a very sticky situation.

Sciency Words A to Z: Rare Earth Hypothesis

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, R is for:


Once upon a time, it was believed that the Sun, Moon, planets, and all the stars revolved around the Earth.  This was known as the geocentric theory.

Copernicus, Galileo, Kepler, and others set us straight about our planet’s physical location in space.  However, it is still sometimes asserted that Earth is special or unique in other ways.  Such assertions are often referred to in a derogatory sense as “geocentrisms.”

It’s tempting to dismiss the Rare Earth Hypothesis as just another geocentrism.  The idea was first presented in 2000 in a book called Rare Earth: Why Complex Life is Uncommon in the Universe by Peter Ward and Donald Brownlee.  In that book, Ward and Brownlee go through all the conditions they say were necessary for complex life to develop on this planet.  Crucially, they point out all the ways things could have gone wrong, all the ways complex life on Earth could have been prematurely snuffed out.

In other words, we are very, very, very lucky to be here, according to Ward and Brownlee, and the odds of finding another planet that was as lucky as Earth must be astronomically low.  Sure, there might be lots of planets where biology got started. Simple microorganisms may be quite common.  But complex, multicellular life like we have here on Earth—that’s rare.  And intelligent life forms like us are rarer still.  Perhaps intelligent life is so rare that we’re the only ones.

My favorite response to the Rare Earth Hypothesis comes from NASA astronomer Chris McKay.  In All These Worlds Are Yours, McKay’s argument is described as the Rare Titan Hypothsis.

Imagine intelligent life has developed on Titan (such a thing seems unlikely, I know, but there may be something living on Titan).  Titanian scientists look through their telescopes and soon realize that no other world in the Solar System is quite like their own.  Earth, for example, if too hot for life as the Titanians know it, and there’s far too much of that poisonous oxygen in the atmosphere anyway.  Furthermore, water would wreak havoc on what the Titanians would consider a biomolecule.

Perhaps a pair of Titanian scientists then decide to publish a book.  They list all the conditions required for complex life to develop on Titan, point out all the ways Titanian life could have been snuffed out prematurely, and argue that the odds of finding another Titan-like world must be astronomically low.

Personally, I think there’s some validity to the Rare Earth Hypothesis, but McKay’s point is worth bearing in mind.  There could be many different ways for life to develop in our universe.  Earth is but one example.  Planets that are just like Earth may indeed be rare—extremely rare—but there’s no reason to conclude that Earth-like life is the only kind of complex life out there.

Next time on Sciency Words A to Z… oh my gosh, we’ve finally made it to S!  It’s finally time to talk about SETI!

Sciency Words A to Z: Panspermia

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, P is for:


Pictured above is a tardigrade, also known as a water bear.  Tardigrades are pudgy-looking, almost cuddly-looking (depending on the photograph) microorganisms that reside here on Earth.  But due to some alleged confusion about their genetic lineage, it was at one time speculated that tardigrades might have come from somewhere else.  Perhaps they migrated to Earth through a process called panspermia.

The word panspermia goes all the way back to ancient Greece, and it can be translated to mean “seeds everywhere,” as in the seeds of life have spread all over the universe.  According to this article by Chandra Wickramasinghe, one of the leading proponents of the panspermia hypothesis, serious scientific discussion of the idea began in the late 1800’s.  In Wickramasinghe’s article, Lord Kelvin is quoted thusly:

… Hence, and because we all confidently believe that there are at present, and have been from time immemorial, many worlds of life besides our own, we must regard it as probable in the highest degree that there are countless seed-bearing meteoritic stones moving through space.  If at the present instant no life existed upon the Earth, one such stone falling upon it might, by what we blindly call natural causes, lead to its becoming covered with vegetation.

While Lord Kelvin and other late 19th and early 20th Century scientists may have taken panspermia seriously, the idea soon fell out of vogue.  Yes, from time to time, perhaps a “meteoritic” impact or a volcanic explosion (or maybe even a really strong gust of wind) might loft a few bacterial spores into a planet’s upper atmosphere.  Perhaps those spores could then escape into space.  But surely those spores would not survive for long after that.

It was British astronomer Fred Hoyle and Sri Lankan-born British astronomer Chandra Wickramasinghe who repopularized panspermia in the 1970’s and 80’s.  As explained in this paper, titled “Progress Towards the Vindication of Panspermia,” the Hoyle-Wickramasinghe interpretation of panspermia is founded on two basic premises: that microorganisms “have an almost indefinite persistence and viability,” and that once they find themselves in the right environment, “microbes can replicate exponentially.”

I’d say both of those premises make sense.  We all know how rapidly microbes can replicate given the chance.  As for their “almost indefinite persistence and vitality”… tardigrades famously survived in the vacuum of space.  No air, no water, extreme temperatures, extreme radiation… the tardigrades handled space quite well. Other microorganisms also survived similar experiments.

But could these microbes survive the thousands or perhaps millions of years it would take to travel from one planet to another?  Hoyle and Wickramasinghe clearly thought so, and they made some pretty outrageous claims about how much biological material we should expect to find drifting through open space.

[…] by 1983 we inferred confidently that some 30 percent of the carbon in interstellar dust clouds had to be tied up in the form of organic dust that matched the properties of degraded or desiccated bacteria.

Panspermia is now one of the most important concepts in the field of astrobiology.  It’s gained a lot of credence, especially since the discovery of those bacteria shaped objects in the ALH84001 meteorite.  However, although it is an important concept, it also remains highly speculative.  As I’ve said several times now in these A to Z posts, astrobiologists must hold themselves to the same standards as a court of law: proof beyond a reasonable doubt.  And there are still plenty of reasonable doubts about panspermia.

Next time on Sciency Words A to Z, call me old fashioned, but I prefer it when planets have names.

Sciency Words A to Z: Noachian

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, N is for:


In the 1870’s, Italian astronomer Giovanni Schiaparelli began producing the most detailed and accurate maps of Mars anyone had ever seen.  Schiaparelli also assigned many of the names we still use today for Martian surface features today. One of those regions on Schiaparelli’s map got the name Noachis Terra—the Land of Noah.

In my opinion, no other name could have turned out to be more apt.  Schiaparelli got many of his names from the Bible, and I’m sure you remember the biblical story of Noah and the Great Flood.

Schiaparelli’s map of Mars.

Much like the geological history of Earth, Mars’s geological history is divided up into different periods.  Noachis Terra spawned the name for Mars’s Noachian Period, a time that roughly corresponds with the Archean Eon here on Earth—the time when the very first microbes were appearing on our planet.

So what was happening on Noachian Mars?  Based on the evidence presented in this textbook on Astrobiology, it wasn’t quite like the Great Flood in the Bible, but it was close!  Most if not all of Mars’s northern hemisphere was probably covered in water.  Circumstantial evidence of shorelines can be seen today.

And in the southern hemisphere, in regions like Noachis Terra, we see unambiguous evidence of ancient flowing water.  Craters show obvious signs of erosion.  There are dried up lakes and rivers, and those rivers appear to have been fed by tributaries, which tells us it used to rain on Mars.

And there’s more.  Many Noachian-aged minerals and rock formations are most easily explained if we assume there was water.  In some cases, water is the only possible explaination.  Our Mars rovers have found mudstone, clay minerals, sedimentary rock… iron and magnesium carbonate… hematite, jarosite, and more!  Some of these minerals would have required a hot and slightly acidic environment, like you might find in a hot spring or near a hydrothermal vent.

We shouldn’t jump to conclusions.  After all, there’s still so much we don’t yet know about Mars, and new discoveries are being made all the time.  But I’m going to go ahead and call a spade a spade here: Noachian Mars sounds an awful lot like Arcean Earth, and it’s easy to imagine that whatever was happening on Arcean Earth (by which I mean LIFE!!!) must’ve also been happening on Noachian Mars.

However, the Noachian Period did not last long—a mere 400 million years.  Earth and Mars have had very different geological histories since then.  After the Noachian, Mars rapidly lost its internal heat, its atmosphere, and its oceans.  By the time of Earth’s Cambrian explosion, when complex, multi-cellular organisms really “exploded” onto the scene, Mars had fully transformed into the barren, inhospitable world we know today.

Modern day Mars has been trying really hard to get our attention and convince us that it might still support life.

And maybe that’s true.  During the Noachian, life had a great opportunity to get started on Mars, and it’s possible that some isolated remnant of a Noachian ecosystem has persisted to this day.  But in my opinion, it’s far more likely that we’ll find fossils left over from the Noachian Period (assuming we haven’t found some already).

Next time on Sciency Words A to Z, did you know there’s a deadly chemical in the air you breathe?  It’s called oxygen.

Sciency Words A to Z: Earth Similarity Index

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, E is for:


From time to time, you might hear on the news that scientists have discovered a new Earth-like planet.  You’d think that would be huge news, but it’s rarely presented that way.  It’s more like a fluff story, the kind of thing news anchors can banter about before tossing to weather.  It’s enough to make you wonder what, exactly, the term Earth-like planet really means.

In 2011, this paper appeared in the journal Astrobiology.  The authors of that paper proposed a new system for quantifying how Earth-like another planet is.  They called their system the Earth Similarity Index or E.S.I.  The basic idea is you take four measurable properties—a planet’s mass, density, surface gravity (represented by escape velocity), and surface temperature—plug that information into an equation, and get a number between zero and one.

Numbers close to zero represent planets that are about as un-Earth-like as possible.  Numbers close to one represent planets that are almost exact matches for Earth. So in most cases, when people talk about Earth-like planets, what they mean are planets that scored highly on the E.S.I.

Unfortunately, because of the limits of current technology, a lot of guesswork has to go into our E.S.I. calculations.  Most of the time, we just can’t get the precise measurements we need.  Measuring a distant exoplanet’s surface temperature seems to be especially problematic.  But even if that weren’t the case, the E.S.I. still wouldn’t account for things like a planet’s atmosphere or the presence of liquid water, or many other key things that make Earth the planet that it is.

That same 2011 paper also proposes another system called the Potential Habitability Index or P.H.I.  Taken together, the E.S.I. and P.H.I. should give you a clear idea of just how Earth-like another planet really is.  A very clear idea.  But the stuff you have to measure for the P.H.I.—we’re not even close to being able to measure that stuff.  Not yet.

Someday in the future, as we continue to refine out observational techniques, maybe we’ll be able to put the E.S.I. and P.H.I. to good use.  Until then, any news you hear about newly discovered Earth-like planets is probably not as exciting as it sounds.  Unless, of course, this is the newscast you’re watching:

Next time on Sciency Words A to Z, nuclear physicist Enrico Fermi said it first: where is everybody?

Sciency Words A to Z: Astrobiology

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, A is for:


If you’ve ever looked up at the night sky and asked yourself if someone or something might be out there gazing back at you, you’re not alone.  Lot’s of people wonder about that.  Some of those people are scientists—a very special kind of scientist called an astrobiologist.  And those astrobiologists are busily working to find an answer.

In my previous A to Z Challenge, we looked at a lot of scientific terms that don’t quite make sense, like this one or this one. Scientists aren’t always the best at naming things.  Astrobiology is yet another term that people sometimes complain about, because based on a strict translation of the Greek root words, astrobiology should mean the study of life on stars.

And that’s absurd.  Nobody expects to find life on or inside of a star.  Rather, astrobiologists are looking for life on planets and moons, and perhaps also asteroids and comets.  And maybe interstellar dust particles.  But not stars.  Definitely not stars!

To quote from All There Worlds are Yours by Canadian astronomer Jon Willis:

The science of astrobiology has three main goals: to understand the conditions necessary for life on Earth (and perhaps the conditions required by life in general), to look for locations in the universe which supply these conditions, and, finally, to detect life in these locations.

The word astrobiology was coined in 1953 by Russian astronomer Gavriil Adrianovich Tikhov, who’s described in this paper from Interdisciplinary Science Reviews as “an unusual beacon of scientific individualism in a sea of Soviet imposed conformity.”

According to that same paper, the term didn’t really catch on in the West until the 1990’s.  The establishment of NASA’s Astrobiology Institute in 1998 seems to have been a key turning point in the history of this word (prior to that, the scientific search for alien life was generally known as exobiology).

Next time on Sciency Words A to Z, we’ll find out what happened in the 1990’s that made NASA so keen to set up its own Astrobiology Institute.  Until then, keep looking up, and keep wondering!

Sciency Words: A to Z Theme Reveal

Hello, Internet friends, and a very special hello to those of you who will, I hope, become new Internet friends!  Today I’m revealing my theme for this year’s A to Z Challenge, and that theme will be Sciency Words.  Specifically, I want to talk about scientific terms related to the search for and study of alien life.

Now before we go any further, I want to make one thing clear: when I talk about the search for alien life, I am not talking about this guy:

No, I’m talking about legitimate scientists doing legitimate scientific research.  No conspiracy theories, no pseudoscience.  The search for alien life is part of a relatively young branch of science that was originally called exobiology and was later renamed astrobiology.

Now some of you may be thinking there’s a problem.  As American biologist and paleontologist George Gaylord Simpson said in 1966, “[…] this ‘science’ has yet to demonstrate that its subject matter exists!”  That’s not an unfair criticism.  We have yet to discover a single alien organism for astrobiologists to study.  Not one.  And as of yet, we have no credible evidence that there are any alien organisms out there to study at all.

Yet astrobiologists already have a lot of work to do trying to answer what might be called preliminary questions.  Questions like:

  • Where might alien life be hiding?
  • What should we be doing to find it?
  • How will we know we’ve found it, assuming we ever do?

That last question may be the toughest of all. At the moment, we only know about life here on Earth.  Aliens might turn out to be so biochemically dissimilar from us that we might not even recognize them as alive!

So starting on April 1st, I hope you’ll join me on this adventure into space.  Hopefully we’ll all learn something about the universe, and about the kinds of life that might be living in it. Or at least I hope we can all expand our scientific vocabularies together!

P.S.: I did a lot of writing for this ahead of time, so fingers crossed that astrobiologists do not announce the discovery of alien life before the end of April.  If they do, it’s going to be a nightmare for me to rewrite all this stuff!

Sciency Words: Alien

Welcome to another episode of Sciency Words, a special series here on Planet Pailly where we take a closer look at the defintions and etymologies of science or science-related terms so we can expand our scientific vocabularies together.  Today’s term is:


I recently added a new book to my personal reference library. It’s called Brave New Words: The Oxford Dictionary of Science Fiction.  Flipping through this book has been an absolute joy, and I’ve learned that many of the words we commonly see in both science and science fiction have far more complicated origins than you might expect.

The First Planet Had the First Aliens

The notion that life might exist on other worlds has been around for a surprisingly long time.  The ancient Greek philosophers were philosophizing about it as far back as the 7th Century B.C.E.  The idea really came to the forefront, though, thanks to Galileo.

Once Galileo looked through his telescope and found that the Moon was covered in mountains and “seas,” and once he turned his attention to the planets and realized they too were worlds in their own right, it wasn’t such a huge leap of logic to supposed that people might be living on those other worlds.  But if we’re going to talk about these hypothetical people, what should we call them?

According to Brave New Words, the planet Mercury was the first to have its possible inhabitants named.  Dutch astronomer Christiaan Huygens was writing about the Mercurians as early as 1698.  The term Lunarians, referring to the inhabitants of the Moon, is first noted in 1708.  Other terms like this kept cropping up throughout the 18th and 19th Centuries: Saturnians in 1738, Neptunians in 1870, Martians in 1874….  But what about a generic term for any life-form that’s not from Earth?

An Alien by Any Other Name

The word alien is almost as old as the concept of extraterrestrial life, but that’s not what the word originally meant at all. “Alien” traces back to an ancient Latin word that meant something like “belonging to someone else,” according to

The word came to English by way of French, with its meaning changing and expanding quite a bit along the way.  Alien can mean strange or exotic.  It can mean new and unexpected.  It can mean “from a foreign land.”  It can also mean out of place or unwelcome, and it can have other pejorative connotations as well.

But for our purposes, we’re primarily interested in the “creature from another planet” definition.  The oldest citation given in Brave New Words comes from British essayist Thomas Carlyle, who wrote in 1820: “I am like a being from another planet on this terrestrial ball, an alien, a pilgrim among its possessors.”

But this quotation is marked as being of historical interest, not as a proper example of the word’s sciency/science fictiony usage.  Mr. Carlyle is sort of fumbling for words here, I think, and the word alien still seems to have more to do with being foreign in general rather than extraterrestrial in particular.

Attack of the Bug-Eyed Monsters

So it’s not until the 1930’s, thanks in large part to the pulp Sci-Fi magazines of that era, that the word alien truly comes to mean a creature from some other world.  As Brave New Words shows us, it’s in the 30’s that we start reading about “intelligent aliens” who perform experiments using “many forms of apparatus,” or we hear about how “disgusting” it would be to “traffic with an alien form of life,” or how infuriating it is to think that a human being has become “a captive of the aliens.”

I don’t know about you, but to me that seems like a surprisingly recent development in the language.

The Big Martian Maybe

Could life exist on Mars?  There’s plenty of compelling evidence that it could, and also plenty of compelling evidence that it could not.  As a result, we’re left with a big, fat maybe. Perhaps the biggest, most frustrating maybe in all of modern science.

After last month’s announcement that the Curiosity rover had found large, complicated organic chemicals on Mars, I was initially tempted to add another point to the “yes, life could exist on Mars” column. But then I read the actual research (which is excellent, by the way).  At this point, I think the only thing we can say for certain is that the big maybe about Mars is even bigger and even more maybe-like.

The Curiosity rover dug up some samples from Martian mudstone, samples that apparently contained organic macromolecules.  What are macromolecules?  For now let’s just say they’re very big molecules.  We can dive into the technical details of what defines a macromolecule in Friday’s episode of Sciency Words.

The problem, as I understand it from that research paper, is that these macromolecules were too big for Curiosity’s instruments to analyze.  So Curiosity destroyed the molecules through a process called pyrolysis (also coming soon to Sciency Words) and analyzed the bits and pieces as they broke apart.  Even those bits and pieces were difficult for Curiosity to study because there were so many of them, but for the most part they seemed to be aromatic compounds made of carbon, hydrogen, and sulfur.

These are the kinds of organic materials that could be deposited on a planet by meteor impacts.  They could also have formed through rather ordinary geological processes.  Or they could be the residue left behind by some kind of biological activity.  And there doesn’t seem to be any way to know for sure where these organics came from based solely on the data Curiosity was able to collect.

So we’re still left with a big maybe.  However, it was once thought by some that the Martian environment was too harsh to preserve these sorts of molecules at all.  Thanks to Curiosity, we now know Mars can and does preserve its organic macromolecules.

And that means that if Mars has had any sort of biological activity, either in the past or present, the chemical record of that activity should be there for us to find.  A definitive yes or no to our question is possible!  We just have to keep digging.