Molecular Monday: The Imaginary Sulfide Ion

February 26, 2018

Just when I feel like this chemistry stuff is starting to make sense to me, I learn something new that makes me feel like I don’t understand it at all. Maybe I’m not the only one. Maybe even the professional chemists feel the same way sometimes. With that in mind, it’s time for another episode of Molecular Mondays.

This month (February, 2018), a paper was published by the Royal Society of Chemistry that casts doubt on a longstanding assumption made by chemists. It involves the S-2 ion in aqueous solutions.

First off, this may have been the most amusing scientific paper I’ve ever had the pleasure of reading. No, the authors didn’t make any references to unicorns, but they did mention something about fairies at the bottom of a well, and then there was this delightful quote: “[…] there has been a growing awareness amongst solution chemists that the S-2(aq) emperor may have no clothes.”

As I understand it, the existence of an aqueous S-2 ion is the kind of thing that makes sense on paper. It allows chemists to easily balance their chemical equations, and it’s been included in textbooks and chemical computer databases for so long now that everyone just takes it for granted that the thing exists.

But apparently the experimental evidence of this particular ion was lacking, and aqueous solutions incorporating several different sulfide compounds did not produce any S-2 ions. At least not according to a Raman spectroscopic analysis.

Now as I’ve written before, papers like this should NOT be interpreted as final proclamations handed down from the ivory tower of science. Rather, this kind of paper should be understood as the beginning of a conversation among scientists. Does this S-2(aq) ion exist or not? If not, how many prior scientific studies need to be reexamined?

There will be further research, and perhaps a rebuttal will be published. Then there will be a rebuttal to the rebuttal, and so forth. But I think, regardless of how this plays out, that this is a good reminder that in science—as in life—what makes sense on paper does not necessarily work in the real world.

Molecular Monday: Quasar-Induced Chemistry

February 12, 2018

Today’s post is part of a bi-weekly series here on Planet Pailly called Molecular Mondays, where we take a closer look at the atoms and molecules that make up our physical universe.

As a science fiction writer, one of the things I’m really doing with my research is trying to find excuses to break the laws of physics. So anything that might produce a previously unknown material substance, a substance that might be imbued with properties that are useful for storytelling purposes… that sort of thing is of great interest to me. With that in mind, I recently read a news article about quasars and the weird, unexpected chemical reactions they can cause.

Quasars are black holes with disks of superheated gas and dust swirling around them. Due to the intense heat of the disk, the extreme gravity of the black hole, and the crazy electromagnetic field the two produce together, you end up with these twin laser-like jets of super-accelerated particles shooting away from the quasar in opposite directions.

According to this research paper published in the Monthly Notices of the Royal Astronomical Society, and according to this slightly less technical summary from Physics World, any molecules that happen to get caught in a quasar’s laser beams are ripped apart by a process known as photolysis. Then, after these quasar-zapped particles have had some time to cool off, they can recombine to form new molecules.

I was led to believe by the initial news report I read that this sort of extreme scenario might also cause atoms to recombine in ways that they normally wouldn’t. Unfortunately I don’t see anything in the actual research to back that up. For the most part, quasar chemistry produces fairly ordinary molecules like hydroxyl, carbon monoxide, and molecular hydrogen.

Still, for the purposes of science fiction, some sort of quasar-induced chemical reaction producing strange, new, potentially valuable chemical substances… that may be too awesome of a concept for me to pass up.

Molecular Monday: Top 5 Chemicals on Mars

January 29, 2018

For today’s Molecular Monday post, I thought I’d try something a little different. I’m counting down my picks for the top five chemicals on Mars. These are chemicals that, in one way or another, are important to helping us understand the Red Planet better.

#5 Possible Methane
Several robotic probes have detected burps of methane on Mars, which could indicate ongoing biological or geological activity—either one of which would be a huge surprise on a world long thought to be both biologically and geologically dead. However, the methane could also be a contaminant leaking from the robots themselves. We’ll have to wait and see with this one.

#4 Hematite
Hematite is a rusty red colored mineral, also known as iron oxide or iron (III) oxide. Almost the entire surface of Mars is covered in hematite, giving the planet its distinctive color. But questions remain about where all this hematite came from. One thing we can be certain about is that Mars’s red color is only skin deep. When the Curiosity rover drilled a hole in the ground, it found the underlying layer was grey.

#3 Carbon Dioxide
Mars’s atmosphere is almost all carbon dioxide, which should help keep the planet warm, but the air is too thin to produce much of a greenhouse effect. As a result, Mars is a little too cold for human comfort. There’s also plenty of frozen CO2 (also known as dry ice) at the poles. Maybe someday we can release all that excess CO2­ and do to Mars what we hope not to do to Earth.

#2 Perchlorate Salts
The most noteworthy perchlorates on Mars are calcium perchlorate and magnesium perchlorate, but there are plenty of other flavors besides those two. Based on data collected all over Mars, it seems these perchlorate salts make up 0.5% to 1.0% of the Martian regolith; that makes the regolith extremely toxic to humans, and we need to figure out what to do about this problem before we can begin any serious colonization efforts. On the other hand, in the unlikely event that life already exists on Mars, perchlorates might (might!) make a good source of chemical energy, similar to the way oxygen is a good source of chemical energy for us.

#1 Water
Humans on Mars will not suffer from a lack of water. There are vast quantities of H2O frozen at the poles and buried in underground glaciers. And there’s little doubt that liquid water once flowed over the planet’s surface, carving river channels and chemically altering the rocks. However, a wet and watery Mars would have looked very different from modern Earth. Rather than standing lakes and rivers, Mars seems to have experienced violent flash floods, perhaps caused by melting and refreezing glaciers, followed by long periods of dryness. Still, the liquid water was definitely there, and there’s a distinct possibility that microorganisms could have started to evolve before the planet dried up completely.

So those are my picks for the top five most interesting and/or important chemicals on Mars. Let me know what you think of this list in the comments, and if people like it, maybe I’ll do something similar for other planets.

P.S.: Honorable mention to the polycyclic aromatic hydrocarbons (PAHs) from the Martian meteorite ALH84001. Like those methane burps, PAHs could either be an indicator of Martian life or a hugely embarrassing scientific mistake.

Molecular Monday: Jarosite on Mars

January 15, 2018

Today’s post is part of a bi-weekly series here on Planet Pailly called Molecular Mondays, where we take a closer look at the atoms and molecules that make up our physical universe.

Over the last few months, I’ve been trying to get to know the planet Mars better. There’s some pretty clear evidence that Mars used to be a different kind of planet, a wetter and more watery sort of world… but perhaps not in the way you might have expected.

Many of Mars’s rocks seem to tell a similar story about that wet, watery past. That story usually begins something like this:

We’ve already looked at Mars’s sedimentary basaltic rocks. Such a thing would be almost a contradiction in terms on Earth. Sedimentary rocks are made by flowing water; basalt is destroyed by water. So how could a rock be both basaltic and sedimentary?

Now let’s take a look at another rock that’s almost self-contradictory: jarosite. Jarosite is a potassium/sulfur/iron-containing mineral with the chemical formula KFe3(OH)6(SO4)2. It typically forms in wet, acidic environments by the oxidation of iron sulfides. If you don’t understand what that means, that’s okay; I don’t fully understand it either. The important thing is that jarosite forms in water; but jarosite is also destroyed by water. It breaks down into simpler compounds if exposed to water for long periods of time. That makes jarosite pretty hard to find on Earth, but of course it’s surprisingly common on Mars!

In 2004, the Opportunity rover discovered jarosite—lots of jarosite—in the Meridiani Planum region (incidentally, the same region where Airy-0 is located). According to a NASA press release at the time: “Jarosite may point to the rocks wet history having been an acidic lake or an acidic hot springs environment.”

But whatever was happening in Meridiani Planum, the region must have dried up pretty quickly. According to the abstract of this paper, also from 2004, “[…] the presence of jarosite combined with residual basalt at Meridiani Planum indicates that the alteration process did not proceed to completion, and that following jarosite formation, arid conditions must have prevailed.”

Before I started all this Mars research, I imagined ancient Mars as a very Earth-like place, with standing oceans and lakes and gently flowing rivers. I guess there still could have been a time like that in the very beginning, but most of Mars’s history with water seems to have been far more sporadic and violent than that, with lots of flash flooding (perhaps caused by melting glaciers) and very brief wet spells followed by long periods of dryness.

At least that’s my impression at this point in my research.

Molecular Monday: Mars Burps Methane

January 1, 2018

Happy New Year’s, and happy Molecular Monday too! I can’t think of a better way to start off 2018 than with a blog post about molecules. Well, no… I probably could, but my schedule says this is what I’m supposed to blog about today, so here we are!

If you’re looking for life on other planets, one of the most common pieces of advice you’ll get is “follow the water.” That is, of course, assuming you can find any liquid water in the first place. But maybe another option is to follow the methane.

The planet Mars seems to have a bit of a methane mystery going on. Mars will sit there, all quiet and normal, for years at a time, but then suddenly…

… and then suddenly all this methane shows up in the planet’s atmosphere.

The most notable of these methane burps occurred in late 2013 and early 2014, when the Curiosity rover started detecting methane levels ten times higher than normal. Where did all this methane come from?

One boring possibility is that it came from the rover itself, a result of some kind of leak. It’s also possible that a meteorite just happened to land near Curiosity, and that this meteorite just happened to be carrying a lot of organic material. Or maybe there was some kind of surprise geological activity nearby that vented methane from somewhere underground.

But the most intriguing possibility is that the methane was produced by biological activity. That is, after all, how most atmospheric methane is produced on Earth. And I recently found this paper offering a possible way to determine once and for all (maybe, hopefully, fingers crossed) if Mars’s methane really does come from a biological source.

From what I gather, having only skimmed through this paper (sorry, I was trying to read this on New Year’s Eve, and there were margaritas), the key is to follow the methane then follow the hydrogen. So the next time Mars burps up some methane, the ratio of methane to hydrogen in the air might reveal the methane’s true source.

Molecular Monday: Perchlorate Salts on Mars

December 18, 2017

Today’s post is part of a bi-weekly series here on Planet Pailly called Molecular Mondays, where we take a closer look at the atoms and molecules that make up our physical universe.

It’s hard to imagine how anything could survive long on Mars. This has been especially true ever since 2008, when the Phoenix Lander conducted the first ever wet chemistry experiment on Martian regolith and detected a chemical called calcium perchlorate.

I haven’t looked into how this wet chemistry experiment worked, but I’m guessing it involved mixing water with a sample of Mars dust and then running a spectroscopic analysis.

Of course when this calcium perchlorate was detected, the first question was: did Phoenix contaminate its own sample? On Earth, perchlorates are an increasingly common pollutant produced by (among other things) rocket fuel. But if there was any serious contamination of the Phoenix landing site due to Phoenix’s landing rockets, we’d expect to find ammonium perchlorate, not calcium perchlorate.

Also subsequent experiments and observations by the Spirit and Opportunity rovers, the Mars Odyssey orbiter, and other Mars missions have found that chlorine is scattered all over the planet. Most of that chlorine is likely bound up in perchlorate form, and it’s now estimated that calcium perchlorate, magnesium perchlorate, and other perchlorate salts make up anywhere between 0.5% and 1% of the Martian regolith.

For humans, that’s an alarmingly high percentage. More than enough to kill you, or at least to cause you serious thyroid problems. But if you’ve been following along with my blog, you know I’ve been living on the surface of Mars and growing my own food here for over a month now. So why am I not dead?

Well… it turns out there is life here on Mars, and the natives have been surprisingly helpful. More about that in my next post.



Molecular Monday: Basalt as a Sedimentary Rock

December 4, 2017

I had a rough week last week, which disrupted my regular posting schedule. But I’ll talk about that on Wednesday for IWSG.

Today I’ve returned to Mars and I’m ready to continue my exploration of the Martian surface. I considered calling today’s post Mineralogical Monday, but really minerals are just a special kind of molecule, so I’ll stick to the Molecular Monday series I already have going.

Before I was so rudely brought back down to Earth, I was visiting Gale Crater. I wanted to meet the Curiosity Rover and maybe get an autograph, but I got distracted by some peculiar rocks.

It’s hard to put into words what was so odd about these rocks. They have the look and feel of sedimentary rocks, but in terms of chemical composition they’re more like basalt. But basaltic sedimentary rock is a contradiction in terms.

Sedimentary rocks form (typically) when sediment accumulates at the bottom of a river, lake, or other body of water. Over time, the sediment becomes compacted or cemented together, and thus a new rock is born.

Basalt is an igneous rock, meaning it forms from cooling magma, and it is chemically vulnerable to water. Basalt tends to include a lot of iron, magnesium, and calcium; water tends to leech these elements out of basalt, leaving a silicon-rich clay behind. So as a sediment sitting at the bottom of a lake or river, basalt wouldn’t last long enough to turn into sedimentary rock.

Fortunately for me, I’m not the only one who’s struggled to find the right terms to describe these weird Martian rocks. Emily Lakdawalla, a well respected science journalist writing for the Planetary Society, wrote an article about this and summed up the inherent contradiction well: “Sedimentary rocks say ‘Mars was wet.’ Basaltic composition says ‘Mars was dry.’”

So how did these basalt-like sedimentary rocks form? I can think of three possibilities:

  • Windblown Sediment: Sedimentary rocks can be created by wind rather than water, but as Emily Lakdawalla shows in her article, not all of these Mars rocks can be explained that way.
  • Liquids Other Than Water: It’s possible the sediment was deposited by a liquid other than water. That explanation makes more sense to me on a super-cold planetoid like Titan, where water is a rock and rivers are full of methane; however on Mars, water still seems to be the most likely working fluid.
  • Flash Floods: Maybe basaltic sediment was only exposed to water for a short time, perhaps during the flash floods that seem to have occurred during Mars’s Hesperian Period.

Most of the rock formations in Gale Crater are already believed to be Hesperian-aged, so the flash flooding idea makes the most sense to me. But of course the Curiosity Rover has been here a lot longer than I have, so I’ll be eager to ask her opinion on the matter.