Sciency Words: Tau Level

September 14, 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:

TAU LEVEL

I first came across this term in a press release from NASA’s Jet Propulsion Laboratory.  It has to do with Mars, and the global dust storm that’s been happening there these last few months, and that Mars rover that we may have lost.  But most of all, this tau level thing has to do with Beer.

No, not that kind of beer.

I’m talking about Dr. August Beer, a 19th Century German physicist who studied how light passes through and/or gets absorbed by various substances.  Dr. Beer is best remembered for Beer’s law, which (according to several papers I looked at… click here or here or here) is used to calculate how much sunlight makes it through the Martian atmosphere to reach the planet’s surface.

In those calculations, the Greek letter tau (τ) represents the amount of dust or other particulate matter that’s floating around in the atmosphere.  The more dust in the air, the higher the tau level.  And the higher the tau level, the less sunlight reaches the ground.

As you can imagine, you need to measure the tau level on Mars each day (or rather, each sol) and predict what the tau level will be tomorrow (I mean, solmorrow) if you’re trying to run any sort of surface mission on Mars that depends on solar power.  And in the future, when we have a well-established colony on Mars, don’t be surprised if the term tau level features prominently in the local weather reports.

P.S.: I had an idea that got too convoluted, but I really wanted to make a “don’t drink and drive” joke involving Beer’s law and our possibly wrecked Mars rover.


Lost Opportunity on Mars

September 12, 2018

Over the last few months, a global dust storm has been raging across the surface of Mars.  It started at the end of May and is only now beginning to clear up. It’s been suggested that this was one of the worst storms we’ve ever observed on the Red Planet

The Good News

If you’re worried about the Curiosity rover, don’t be.  The rover’s just kept on roving, and sciencing, and recently it sent back this selfie to let us know everything’s a-okay.

Just kidding.  Here’s a link to the actual “selfie” Curiosity sent back. It’s an interactive 360-degree panoramic thing, so click the image and drag it around to get the full experience.

The Bad News

While Curiosity seems totally unfazed by the bad weather, things are not looking so good for NASA’s other rover, Opportunity.  It’s too early for a eulogy, but based on what it says in this press release from NASA’s Jet Propulsion Laboratory, we should be prepared for the worst.

NASA lost contact with Opportunity in early June, shortly after the storm began.  Unlike Curiosity, which runs on nuclear batteries, Opportunity depends on solar panels for energy.  So the problem may simply be that Opportunity wasn’t getting enough sunlight during the storm.

Or it could be that something more serious has happened to the almost fifteen-year-old rover.  In the press release, Opportunity’s project manager is quoted saying: “If we do not hear back after 45 days, the team will be forced to conclude that the Sun-blocking dust and the Martian cold have conspired to cause some type of fault from which the rover will more than likely not recover.”

So fingers crossed….


How to Walk in Hypogravity

August 29, 2018

As a science fiction writer, I really wish I knew what it’s like to walk on the Moon or Mars or any other low gravity world.  It would help a lot with that whole “writing from lived experience” thing.  Of course there are ways I could experience hypogravity for myself, but I don’t have that kind of money.  So instead, I’ve turned to medical research papers like this one from Frontiers in Physiology.

First off, let me just say this: I’ve read some really complicated stuff over the years, but I don’t think I’ve ever read anything as complicated as a scientific paper trying to describe how we humans walk.

But if we want to understand what it would really be like to walk on another planet, we have to start by understanding—in meticulous mathematical detail, apparently—how we do this walking thing here on Earth.

Gravity Makes Walking So Much Easier

The mathematical relationship between walking speed, leg length, and gravity was determined back in the 1870’s.  It was later used in what sounds like a rather whimsical research paper about the walking pace of the Lilliputians from Gulliver’s Travels.  And then it was used for more pragmatic purposes to estimate the running speeds of dinosaurs.

For those sorts of calculations, the force of gravity would have been treated as a constant, but gravity can easily be treated like a variable, and that’s when things get interesting.  You see, when you walk, your body uses energy to complete the full arc of a footstep, especially at the beginning when you’re lifting your foot off the ground.  But gravity helps you (perhaps more than you realize) when your foot comes back down to the ground.

So if you reduce the force of gravity, gravity provides you with less assistance, and you end up having to expend more energy to complete each step in your walk cycle.

Walking-Mode vs. Running-Mode

The muscle actions involved in walking and running are different enough that there’s no real grey area between “walking-mode” and “running-mode,” as that paper from Frontiers in Physiology calls them. These two “modes of locomotion” take advantage of gravity in distinctly different ways.  Walking-mode ends up being more metabolically efficient at slower speeds, and running-mode is the more metabolically efficient way to travel at higher speeds.

So what happens when you alter the force of gravity?  The transition point where running-mode becomes more efficient than walking-more changes too. Lower gravity means your body will naturally want to switch modes at a lower speed.

On the Moon, for example, walking-mode only works well when you’re moving very slowly.  To achieve what we might consider a normal walking pace, you’ll have to switch to running-mode.  And if you want to reach Earth-like running speed, you’ll probably have to try hopping-mode or jumping-mode—modes of locomotion that we don’t use often here on Earth except under certain specialized circumstances. Skipping-mode also seems to be more metabolically efficient on the Moon than it is on Earth.

Moon-Walking or Mars-Walking in Science Fiction

I’ve read plenty of Sci-Fi stories set on the Moon or Mars. For the most part, I feel like science fiction writers just mention the reduced gravity thing in passing and then move on with the story as quickly as possibly.  I don’t blame them.  It’s really hard to imagine what hypogravity must feel like, and even harder to communicate that feeling to readers.

But one of my highest ambitions as a writer is to write something that makes you feel like you’re there on the surface of a hypogravity planet like Mars.  I want to capture that experience of “running in order to walk” and “hopping in order to run.”  Hopefully this line of research will someday help me pull that off.


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:

MACROMOLECULE

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:

AROMATIC

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!