Sciency Words: Macromolecule

July 13, 2018

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:


After all the years I’ve been writing Sciency Words, I’ve noticed something.  A lot of times it might seem pretty obvious what a scientific term means, but then you dig a little deeper and find that the term is not so clearly or precisely defined as you’d expect.

Defining macromolecule should be easy.  Macro means big, molecule means molecule; ergo, a macromolecule is a big molecule.  But after I read this paper about the discovery of organic macromolecules on Mars, I had a question: just how big does a molecule need to be to get that macro- prefix?

German chemist Herman Staudinger is credited with coining the term macromolecule.  It was a highly controversial concept at the time.  Another German chemist, Nobel laureate Heinrich Wieland, wrote to Staudinger in the 1920’s saying: “My dear colleague, drop the idea of large molecules; organic molecules with a molecular weight higher than 5000 do not exist.”  But Staudinger would later become a Nobel laureate himself for proving that they do.

I take that Wieland quote to mean that the word macromolecule was defined as any molecule with a molecular weight in excess of 5000, but I’ve seen other sources claiming it was defined as any molecule containing one thousand or more atoms, and still other sources saying it’s ten thousand or more atoms.

But those were the kinds of definitions being used in the early 20th Century.  Modern usage gets far more complicated and confusing.  As Wikipedia explains, the definition of macromolecule “varies among the disciplines.”

  • In biology, there are four kinds of macromolecule: lipids, proteins, nucleic acids, and carbohydrates. If it’s not one of those four things, it’s not a macromolecule, according to a biologist.
  • Polymer scientists go by a definition set by the International Union of Pure and Applied Chemistry (IUPAC), which states that a macromolecule is a “molecule of high relative mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass.”
  • Wikipedia also mentions a definition that involves aggregates of molecules sticking securely together due to intermolecular forces rather than covalent or ionic bonds.

It’s not unusual for one word to be defined in different ways by different fields (see my post on metallicity).  This is a big reason why some scientific terms end up being so difficult to define.

As for those organic macromolecules Curiosity found on Mars… in the context of that research, I think macromolecule simply means “very big molecule.”  Like I said on Wednesday, we don’t really know what, specifically, Curiosity found, and maybe we never will.  We just know that it must’ve had a lot of very big molecules in it.

The Big Martian Maybe

July 11, 2018

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.

Sciency Words: Aromatic

July 6, 2018

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 when I was a little kid, I discovered that gasoline doesn’t smell terrible.  In fact, it has an almost sweet aroma to it.  I got in a lot of trouble for this because, for obvious reasons, my parents didn’t want me sniffing gas fumes.  But still, that subtly sweet smell is there, and it’s caused by a chemical known as benzene.

Apparently I’m not the only person to take note of benzene’s smell.  German chemist Augustus Wilhelm Hofmann is credited with the first usage of the word “aromatic” to describe benzene, along with a whole host of other sweet-smelling chemicals.

Hofmann seems to have realized not only that these chemicals smelled similar but also that they had similar chemical compositions.  “Of this series,” Hofmann wrote in 1855, “few members are at present known, but the group of aromatic acids is itself very imperfect and limited.”  In other words, Hofmann predicted the existence of more “aromatic” chemicals that should fit the pattern.

And more chemicals of this series were later discovered, and we now know what they really have in common: a flattened, ring-like chemical structure, as pictured below:

As an adult, I know better than to sniff gasoline, and as an artist I know better than to sniff my art supplies.  But the xylene used as a solvent in some pens and markers does have that same vaguely sweet aroma as benzene. However, not all of the chemicals we call “aromatic” smell so nice, or smell at all.  It’s the flattened, ring-like structure that defines aromaticity today.  The odor is no longer considered relevant.

You might be wondering then why we still call these chemicals aromatic, if their aromas aren’t important.  This seems to be another case of scientists naming something before they really understood it.  The same thing happened with the word organic.  The term was used so often in scientific literature and became so deeply ingrained in the scientific lexicon that we’re now unable to change it.

The ring-like structures in aromatic chemicals are incredibly strong and unlikely to break apart during chemical reactions. That makes them really good structural components for the large, complex molecules that make life possible here on Earth—and may have once made life possible on Mars.  But we’ll talk more about that next week!

Mars in Review

April 16, 2018

I meant to wrap up my special Mission to Mars series a few weeks ago, but then some stuff happened, and then I got sick, and my whole blogging schedule got messed up.

Anyway, better late then never.

When I launched this mission, I felt like I didn’t know as much about Mars as a space enthusiast/science fiction writer like me should.  I wanted to fix that.  I wanted to immerse myself in everything Martian, and so I did.  For a lot longer than I expected, too.

During that time, I got a much clearer sense of Mars’s history, as told by the geological and chemical evidence.  Without a doubt, Mars was a wet and water world in the distant past, but that does not necessarily mean it was an Earth-like planet. Rather, Mars’s history with water seems to have been brief and violent, with lots of flash flooding caused, perhaps, by the rapid thawing and refreezing of glaciers.

Even so, life could maybe possibly have started to evolve on ancient Mars, and even as the planet dried up, there’s a slim (very slim) chance life could have survived and endured all the way up to the present day. Scientists take this possibility seriously (a lot more seriously than I expected, to be honest), and there’s an active and passionate debate going on about how to explore Mars without contaminating any hypothetical Martian ecosystems with our Earth germs. Two of my favorite posts for this series, “Let a Mars Rover Rove” and “Mars Rovers Must Rove Responsibly,” compared and contrasted the two sides of that debate.

But of course a huge portion of this series was devoted to the future human colonization of Mars.  I wrote several posts about how to get to Mars, reviewing proposals made by Buzz Aldrin (of Moon landing fame), Robert Zubrin (author of The Case for Mars), and Elon Musk (the guy who runs SpaceX).  I also wrote about how future colonists might adapt the calendar to suit the slightly longer Martian day and the significantly longer Martian year. And of course there were all those posts about what kinds of food might be practical on Mars, starting with potatoes and working up to goat cheese.

I’m still no Mars expert.  Mars is the second most thoroughly explored planet in the Solar System, after Earth, and there’s just so much information to sort through.  On top of that, new discoveries are being made all the time.  The already enormous pile of Mars-related knowledge just keeps growing!

But I do at least feel more familiar with the Red Planet, and I hope you do to.  Thank you to everyone who followed along with this series, either for the whole long slog of it or just bits and pieces of it.  If you had any favorite posts from this Mars series, I hope you’ll let me know in the comments.  Also, I’m planning to do “Mars month” again next March, so if you have suggestions about other Mars-related things I should research, let me know!

Dining on Mars, Part 5: Goat Cheese

April 2, 2018

Over the last few months, I’ve been on a mission to learn as much as I can about Mars.  As part of that mission, I wanted to know what sorts of foods might one day be part of a Mars colonist’s diet.

We’ve already talked about potatoes and sweet potatoes. We’ve talked about lettuce and other common vegetables, and we’ve talked about entomophagy, the practice of eating bugs.  Some might balk at that idea, but insects are a highly efficient source of animal protein, and on Mars food production must be as hyper-efficient as possible.

We’ve also talked about seafood, specifically tilapia, another efficient source of animal protein.  I sort of think of tilapia as a Martian “luxury food,” though, because I feel like only a large and prosperous Mars colony could spare the room and resources needed for fish tanks.

But hey, if the human colonization of Mars is a success, more and more luxuries will be introduced.  The people of Mars may well demand it as their colonies start to feel less like research outposts more like a true civilization.  So with that in mind, let’s talk about goats.

In his book The Case for Mars, aerospace engineer Robert Zubrin has this to say about sending goats to Mars:

Some years ago a science writer wrote several books in which he popularized the idea of goats as the key to future animal husbandry in space.  They are of convenient size, omnivorous, fast breeding, milkable, and so on.  Be that as it may, I’m city born, but have lived in the more recent portion of my life in a rural area.  I’ve seen what goats can do.

I’ve tried very hard to figure out which science writer Zubrin was referring to here, but I’ve never found the original source.  Over the past few decades, the only person talking about sending goats to Mars seems to be Zubrin himself, and he only brings up the subject in order to tell us what a terrible idea it is.

You see many of the habitat structures we’ll need to build on Mars will be made of fabric or fabric-like materials, the kind of materials goats are prone to nibble on.  Goats are also known to chew on wires and cables.  Also, given Mars’s reduced gravity, these Mars goats will be able to jump really, really high, as pictured above.

Even so, I like this idea.  Goats don’t require a lot of grazing land, and they can eat much of the food waste we humans can’t digest.  They may not be as nutritionally efficient as mealworms or crickets or tipalia, but they’re still a reasonably efficient food source.

Efficient enough, I think, for the needs and desires of a truly prosperous, truly “civilized” Mars.  Finally, our Mars colonists will have meat and milk and, perhaps most luxurious of all, cheese—because few things say “civilization” better than a well-cultured cheese.

Now if we can just get grapes to grow on Mars, so we can have wine….

Sciency Words: Special Region

March 30, 2018

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:


It’s been several months now that I’ve been focusing almost all my research efforts on Mars. During that time, I’ve read a lot about those very special regions of Mars that might be home to alien life, but I didn’t realize until last week that “special region” is, in fact, a technical term.

Not only that, it’s a term whose precise definition has been and continues to be in dispute—exactly the kind of term most worthy of a Sciency Words post!

According to this paper from the journal Astrobiology, a special region is any region on Mars where “terrestrial organisms are likely to replicate” or where there is “a high potential for the existence of extant martian life forms.” By international agreement, NASA and other space agencies are not allowed to risk contaminating these special regions with our Earth germs. Since our current Mars rovers may not be 100% germfree, they’re all banned from exploring those areas.

But where are these regions, exactly? What are their boundary lines? This is where the definition of this term gets murky. We just don’t know enough about Mars to know which regions are special and which are not.

Initially I assumed it would be up to the International Astronomy Union (I.A.U.) to sort this out. They claim to be the sole authority on naming, categorizing, and defining space stuff. Even if you’ve never heard of the I.A.U. before, I can almost guarantee you’ve heard about at least one thing they did.

But in this case, I guess because this is a matter of international law, it’s a different organization that has to define what is or is not a special region. That organization is called COSPAR (Committee On SPAce Research), which is part of the International Council for Science. And COSPAR has been understandably reticent about setting any official definitions or drawing any official boundaries on a map. Like I said, we just don’t know enough about Mars yet.

Instead, COSPAR recommends evaluating potential landing sites on Mars on a case-by-case basis, keeping the latest scientific data in mind, to avoid contaminating any regions that might possibly someday turn out to be special (whenever we figure out what that means). According to this article from NASA, COSPAR reviews and updates the definition of “special region” every two years. Their next formal meeting is scheduled for July of 2018.

P.S.: Wait a second… who put that sign there? They better have decontaminated it first!

Molecular Monday: Mr. Asteroid’s Organic Delivery Service

March 26, 2018

A lot of what I write about on this blog, and also a lot of what I hope to do as a science fiction writer, comes from reading actual scientific research. Over the years, I’ve gotten pretty good (I think) at wading through all that scientific jargon. But sometimes I invest my time in reading something and… well, it just doesn’t give me a whole lot to work with.

There’s been a lot of press lately about how asteroids and comets deliver loads and loads of organic material to Mars, and what that may mean for our search for Martian life. I thought this would make an excellent Molecular Monday post (today’s post is part of a biweekly series called Molecular Mondays, blah blah, you know the spiel).

But after reading the actual paper, I can’t help but feel that this research has been overhyped.

Don’t get me wrong! It’s good research, as far as I’m able to judge, without any of the usual red flags I’ve learned to watch out for. But it’s based on a computer simulation, a simulation that depends upon quite a few assumptions about asteroid and comet populations in our Solar System. The authors are upfront and honest about this, and they do a good job explaining why they believe their assumptions are justified. This article from IFL Science calls these assumptions “reasonable assumptions,” and that may be true.

But still… this paper makes a lot of assumptions!

The general idea that asteroids and comets deliver organic material to Mars (and other planets) makes sense to me. The conclusion that we should search impact craters on Mars for organics seems sensible enough. It’s just… I don’t know, maybe I’ve missed something important (it wouldn’t be the first time), but with so many assumptions in play, I can’t take any of the specifics from this paper too seriously.

P.S.: I didn’t really talk about chemistry in this post, which is sort of off brand for Molecular Mondays. So I’ll just remind everyone that the word organic does not mean what you may think it means. You can have organic chemicals and organic chemistry without having living organisms.