Only a H2 in A Gilded Cage

“OK, Susan, you’ve led us through doing high-pressure experiments with the Diamond Anvil Cell and you’ve talked about superconductivity and supermagnetism. How do they play together?”

“It’s early days yet, Sy, but Dias and a couple of other research groups may have brought us a new kind of superconductivity.”

“Another? You talked like there’s only one.”

“It’s one of those ‘depends on how you look at it‘ things, Al. We’ve got ‘conventional‘ superconductors and then there are the others. The conventional ones — elements like mercury or lead, alloys like vanadium‑silicon — are the model we’ve had for a century. Their critical temperatures are generally below 30 kelvins, really cold. We have a 60‑year‑old Nobel‑winning theory called ‘BCS‘ that’s so good it essentially defines conventional superconductivity. BCS theory is based on quantum‑entangled valence electrons.”

“So I guess the unconventional ones aren’t like that, huh?”

“Actually, there seem to be several groups of unconventionals, none of which quite fit the BCS theory. Most of the groups have critical temperatures way above what BCS says should be the upper limit. There are iron‑based and heavy‑metals‑based groups that use non‑valence electrons. There are a couple of different carbon‑based preparations that are just mystical. There’s a crazy collection of copper oxide ceramics that can contain five or more elements. Researchers have come up with theories for each of them, but the theories aren’t predictive — they don’t give dependable optimization guidelines.”

“Then how do they know how to make one of these?”

“Old motto — ‘Intuition guided by experience.’ There are so many variables in these complex systems — add how much of each ingredient, cook for how long at what temperature and pressure, chill the mix quickly or anneal it slowly, bathe it in an electrical or magnetic field and if so, how strong and at what point in the process… Other chemists refer to the whole enterprise as witch’s‑brew chemistry. But the researchers do find the occasional acorn in the grass.”

“I guess the high‑pressure ploy is just another variable then?”

“It’s a little less random than that, Sy. If you make two samples of a conventional superconductor, using different isotopes of the same element, the sample with the lighter isotope has the higher critical temperature. That’s part of the evidence for BCS theory, which says that electrons get entangled when they interact with vibrations in a superconductor. At a given temperature light atoms vibrate at higher frequency than heavy ones so there’s more opportunity for entanglement to get started . That set some researchers thinking, ‘We’d get the highest‑frequency vibrations from the lightest atom, hydrogen. Let’s pack hydrogens to high density and see what happens.'”

“Sounds like a great idea, Susan.”

“Indeed, Al, but not an easy one to achieve. Solid metallic hydrogen should be the perfect case. Dias and his group reported on a sample of metallic hydrogen a couple of years ago but they couldn’t tell if it was solid or liquid. This was at 5 megabars pressure and their diamonds broke before they could finish working up the sample. Recent work has aimed at using other elements to produce a ‘hydrogen‑rich’ environment. When Dias tested H2S at 1.5 megabar pressure, they found superconductivity at 203 kelvins. Knocked everyone’s socks off.”

“Gold rush! Just squeeze and chill every hydrogen‑rich compound you can get hold of.”

“It’s a little more complicated than that, Sy. Extreme pressures can force weird chemistry. Dias reported that shining a green laser on a pressurized mix of hydrogen gas with powdered sulfur and carbon gave them a clear crystalline material whose critical temperature was 287 kelvins. Wow! A winner, for sure, but who knows what the stuff is? Another example — the H2S that Dias loaded into the DAC became H3S under pressure.”

“Wait, three hydrogens per sulfur? But the valency rules—”

“I know, Sy, the rules say two per sulfur. Under pressure, though, you get one unattached molecule of H2 crammed into the space inside a cage of H2S molecules. It’s called a clathrate or guest‑host structure. The final formula is H2(H2S)2 or H3S. Weird, huh? Really loads in the hydrogen, though.”

“Jupiter has a humungous magnetic field and deep‑down it’s got high‑density hydrogen, probably metallic. Hmmm….”

~~ Rich Olcott

Zeroing In on Water

<chirp, chirp> “Moire here.”

“Hi, Sy, it’s me, Vinnie. I just heard this news story about finding water on the Moon. I thought we did that ten years ago. You even wrote about it.”

“The internet never forgets, does it? That post wasn’t quite right but it wasn’t wrong, either.”

“How can it be both?”

“There’s an old line in Science — ‘Your data’s fine but your conclusions are … nuts.’ They use a different word in private. Suppose you land on a desert island and find a pirate’s treasure chest. Should the headlines say you’d found a treasure?”

“Naw, the chest might be empty or full of rocks or something.”

“Mm-hm. So, going back to that post… I was working from some reports on NASA’s Lunar Reconnaissance Orbiter. Its LAMP instrument mapped how strongly different Moon features reflected a particular frequency of ultraviolet light. That frequency’s called ‘Lyman‑alpha.’ Astronomers care about it because it’s part of starlight, it’s reflected by rock, and it’s specifically absorbed by hydrogen atoms. Sure enough, LAMP found some places, typically in deepshadow craters, that absorbed a lot more Lymanalpha than other places.”

“And you wrote about how hydrogen atoms are in water molecules and the Moon’s deep crater floors near the poles are sheltered from sunlight that’d break up water molecules so LAMP’s dark spots are where there’s water. And you liked how using starlight to find water on the Moon was poetical.”

“Uhh… right. All that made a lot of sense at the time and it still might be true. Scientists leapt to the same hopeful conclusion when interpreting data from the MESSENGER mission to Mercury. That one used a neutron spectrometer to map emissions from hydrogen atoms interacting with incoming cosmic rays. There again, the instrument identified hydrogen collected in shaded craters at the planet’s poles. Two different detection methods giving the same positive indication at the same type of sheltered location. The agreement seemed to settle the matter. The problem is that water isn’t geology’s only way or even its primary way to accumulate hydrogen atoms.”

“What else could it be? Hydrogen ions in the solar wind grab oxide ions from Moon rock and you’ve got water, right?”

“But the hydrogens arrive one at a time, not in pairs. Any conversion would have to be at least a two‑step process. The Moon’s surface rocks are mostly silicate minerals. They’re a lattice of negative oxide ions that’s decorated inside with an assortment of positive metal ions. The first step in the conversion would be for one hydrogen ion to link up with a surface oxide to make a hydroxide ion. That species has a minus‑one charge instead of oxide’s minus‑two so it’s a bit less tightly bound to its neighboring metal ions. Got that?”

“Gimme a sec … OK, keep going.”

“Some time later, maybe a century maybe an eon, another hydrogen ion comes close enough to attack our surface hydroxide if it hasn’t been blasted apart by solar UV light. Then you get a water molecule. On balance and looking back, we’d expect most of the surface hydrogen to be hydroxide ions, not water, but both kinds would persist better in shadowed areas.”

“OK, two kinds of hydrogen. But how do we tell the difference?”

“We evaluate processes at lower‑energies. Lyman‑alpha photons pack over 10 electronvolts of energy, enough to seriously disturb an atom and blow a molecule apart. O‑H and H‑O‑H interact differently with light in the infra‑red range that just jiggles molecules instead of bopping them. For instance, atom pairs can stretch in‑out. Different kinds of atom bind together more‑or‑less tightly. That means each kind of atom pair resonates at its own stretch energy, generally around 6 microns or 0.41 electronvolts. NASA’s Cassini mission had a mapping spectrometer that could see down into that range. It found O‑H stretching activity all over the Moon’s surface.”

“But that could be either hydroxyls or water.”

“Exactly. The new news is that sensors aboard NASA’s airborne SOFIA mission map light even deeper into the infra‑red. It found the 3‑micron, 0.21‑electronvolt signal for water’s V‑shape scissors motion. That’s the water that everybody’s excited about.”

“Lots of it?”

“Thinly spread, probably, but stay tuned.”

~~ Rich Olcott

To Swerve And Project

A crisp Fall dawn, crisp fallen leaves under my feet as I jog the path by the park’s lake.

“Hey! Moire! How about these red sunrises and sunsets? Remind you of Mars?”

“Morning, Mr Feder. Not much, and definitely not dawn or dusk. Those tend more to blue, as a matter of fact.”

“Waitaminnit, Moire. I seen that Brad Pitt Martian movie, him driving hisself all alone across that big plain — the place is blood‑red.”

“Think a minute, Mr Feder. If he was all alone, who was running the cameras?”

“Uhhh, right. Movie. Yeah, they were really on Earth so they could director the lighting and all. But they said they’d scienced the … heck out of it.”

“Oh they did, better than most movies, but artistic license took over in a couple of places. People expect Mars to be red, not mostly clay colored like it really is, so the producers served up red.”

“Wait, I remember the conversation about Earth is blue because of the oceans and Mars is red because of its rusty atmosphere. So what’s with the sky colors?”

“Looking up at sunlight through an atmosphere is very different from looking down at the surface. It all has to do with how what’s in the atmosphere interacts with sunlight. Take Earth’s blue sky, for instance.”

“My favorite color.”

“Sure it is. OK, the Sun’s disk takes up much less than 1% of the sky but that’s enough to give us all our sunlight photons. A fraction of them run into something on the way down to Earth’s surface. What happens depends on how big the something is compared to the photon wavelength. Much larger things, maybe an airplane, completely block the photons and we get a shadow.”

“Obviously.”

“Yeah, but life’s more interesting for smaller somethings. For things like air molecules and dust particles that are much smaller than the the wavelength of visible light, the waves generally swerve around the particle. How much they swerve depends on the wavelength — extreme blue light bends about ten times more than extreme red light for the same scattering particle. So suppose there’s a kid a few miles away from us looking at the sky while we’re looking at it here. There’s a sunbeam with a rainbow‑load of photons headed for the kid, but there are dust particles in the way. Get the picture?”

“Sure, sure, get on with it.”

“So some of the light swerves. The red swerves a little but the blue light swerves ten times as much, enough that it heads straight for us. What color do we see when we look in that direction?”

“Blue, of course.”

“Blue everywhere in the lit‑up sky except when we look straight at the Sun.”

“What about these pretty red sunsets and the red skies over the wildfires?”

“Two different but related phenomena. Sunsets first. An incoming photon with just the right wavelength may simply be absorbed by a molecule. Doesn’t happen often, but there’s lots of molecules. Turns out that oxygen and ozone absorb blue light more strongly than red light. When we’re looking horizontally towards a sunset we’re looking through many more oxygen molecules than when we look vertically. We see the red part of a blue‑filtered version of that swerve rainbow.”

“And the fire skies?”

“The fires released huge amounts of fine smoke particles, just the right size for color‑scattering. Blue light swerves again and again until it’s either absorbed or shot out to space. Red light survives.”

Upper image – Golden Gate Bay under fiery skies, Sept 2020
Lower image – Sunset from Gusev Crater, Mars
Credit: NASA/JPL/Texas A&M/Cornell

“So what’s different about Mars?”

“Three things — Mars dust is different from Earth’s, its atmosphere is a lot thinner, and there’s practically no atmospheric water or oxygen. Rusty Mars dust is the size of smoke particles. With no rain or snow to settle out the dust, it stays aloft all the time. Rust is red because it absorbs blue light and reflects only the red part. With less diffused sunlight, Mars’ sky is basically the black of space overlaid with a red tint. Sunsets are blue‑ish because what blue light there is can travel further.”

“Earth skies are better.”

~~ Rich Olcott

Question Time

Cathleen unmutes her mic. “Before we wrap up this online Crazy Theories contest with voting for the virtual Ceremonial Broom, I’ve got a few questions here in the chat box. The first question is for Kareem. ‘How about negative evidence for a pre-mammal civilization? Played-out mines, things like that.‘ Kareem, over to you.”

“Thanks. Good question but you’re thinking way too short a time period. Sixty‑six million years is plenty of time to erode the mountain a mine was burrowing into and take the mining apparatus with it.

“Here’s a different kind of negative evidence I did consider. We’re extracting coal now that had been laid down in the Carboniferous Era 300 million years ago. At first, I thought I’d proved no dinosaurs were smart enough to dig up coal because it’s still around where we can mine it. But on second thought I realized that sixty-six million years is enough time for geological upthrust and folding to expose coal seams that would have been too deeply buried for mining dinosaurs to get at. So like the Silurian Hypothesis authors said, no conclusions can be drawn.”

“Nice response, Kareem. Jim, this one’s for you. ‘You said our observable universe is 93 billion lightyears across, but I’ve heard over and over that the Universe is 14 billion years old. Did our observable universe expand faster than the speed of light?‘”

“That’s a deep space question, pun intended. The answer goes to what we mean when we say that the Hubble Flow expands the Universe. Like good Newtonian physicists, we’re used to thinking of space as an enormous sheet of graph paper. We visualize statements like, ‘distant galaxies are fleeing away from us‘ as us sitting at one spot on the graph paper and those other galaxies moving like fireworks across an unchanging grid.

“But that’s not the proper post-Einstein way to look at the situation. What’s going on is that we’re at our spot on the graph paper and each distant galaxy is at its spot, but the Hubble Flow stretches the graph paper. Suppose some star at the edge of our observable universe sent out a photon 13.7 billion years ago. That photon has been headed towards us at a steady 300000 kilometers per second ever since and it finally reached an Earth telescope last night. But in the meantime, the graph paper stretched underneath the photon until space between us and its home galaxy widened by a factor of 3.4.

“By the way, it’s a factor of 3.4 instead of 6.8 because the 93 billion lightyear distance is the diameter of our observable universe sphere, and the photon’s 13.7 billion lightyear trip is that sphere’s radius.

“Mmm, one more point — The Hubble Flow rate depends on distance and it’s really slow on the human‑life timescale. The current value of the Hubble Constant says that a point that’s 3×1019 kilometers away from us is receding at about 70 kilometers per second. To put that in perspective, Hubble Flow is stretching the Moon away from us by 3000 atom‑widths per year, or about 1/1300 the rate at which the Moon is receding because of tidal friction.”

“Nice calculation, Jim. Our final question is for Amanda. ‘Could I get to one of the other quantum tracks if I dove into a black hole and went through the singularity?‘”

“I wouldn’t want to try that but let’s think about it. Near the structure’s center gravitational intensity compresses mass-energy beyond the point that the words ‘particle’ and ‘quantum’ have meaning. All you’ve got is fields fluctuating wildly in every direction of spacetime. No sign posts, no way to navigate, you wouldn’t be able to choose an exit quantum track. But you wouldn’t be able to exit anyway because in that region the arrow of time points inward. Not a sci‑fi story with a happy ending.”

“<whew> Alright, folks, time to vote. Who presented the craziest theory? All those in favor of Kareem, click on your ‘hand’ icon. … OK. Now those voting for Jim? … OK. Now those voting for Amanda? … How ’bout that, it’s a tie. I guess for each of you there’s a parallel universe where you won the virtual Ceremonial Broom. Congratulations to all and thanks for such an interesting evening. Good night, everyone.”

~~ Rich Olcott

Smart Dinosaurs?

<chirp, chirp> “Moire here, what can I do for you while staying six feet away?”

“Hi, Sy, this is Cathleen. you’re invited to to an experiment.”

“What sort of experiment?”

“You’ve been to a few of our ‘Crazy Theory’ events. We can’t do those now, of course, but we’re trying it online. Interested?”

“Sounds like fun. Email me the details and I’ll dial in.”


“Hi, everyone, welcome to our first-ever online ‘Crazy Theories’ seminar. I’m afraid it’ll be a bit different from our traditional affairs. Everyone but the presenter’s on mute so don’t bother shouting encouragement or booing. Any spitballs or wadded-up paper napkins you throw you get to clean up. As always at the end we’ll take a vote to award the Ceremonial Broom for the craziest theory. Type your questions and comments in the chat box; we’ll get to them after the presenter finishes. Everybody got all that? OK, our first presenter is from my Planetology class. Go ahead, Kareem.”

“Hey, everybody. I’m Kareem and my Crazy Theory isn’t mine, personally, but it’s the one that got me into Planetology class. Its was in this science fiction novel I read a couple of years ago. The story’s complicated and has a lot of science that I didn’t understand, but the part that caught my imagination was his idea that what killed off the dinosaurs was smart dinosaurs.”

<consults notes>

“A little history first. In the late 1970s two scientists named Alvarez discovered that all around the Earth there’s a thin layer of soil with more than ten times the normal amount of an element called iridium. They found that the layer was 66 million years old, which just matched the end of the Cretaceous Era when the last of the dinosaurs died off. They knew that some meteorites have a lot of iridium so in 1980 they suggested that a meteor strike must have done the deed.

“That idea was so controversial that John McLoughlin came up with his own explanation and based his book on it. He supposed that about 66 million years ago evolution produced intelligent dinosaurs that took over the planet the way that we humans have in our time. They weren’t huge like T‑rex but they were big enough to use Triceratops as draft and meat animals and smart enough to develop lots of iridium‑based technology like we use copper. Anyway, they got into a world war and that was what wiped everything out and left behind the traces of iridium.”

<gulps down soda>

“McLaughlin’s book came out in 1988. Since than we’ve learned that the Alvarez guys were basically right although there was some other stuff going on, too. But the book got me thinking that maybe there could have been a world‑wide civilization and the only things left after 66 million years were bones and this trace of a metal they used. Humans have only been around for like a hundred thousand years and we’ve only been doing metals big‑time for a few hundred which is teeny compared to a million years. A paleontologist wouldn’t even be able to detect a time period that small. So my Crazy Theory is, maybe there were smart dinosaurs or something and we just haven’t found evidence for them.”

<burp>

“Ever since then I’ve kept an eye out for publications about what a vanished civilization might leave behind for us to discover. In this book Weisman lays out survival times for our civilization’s stuff — plastic, houses, roads and so on. Pretty much everything but Mount Rushmore and the Chunnel will have dissolved or eroded away much sooner than a million years. Really readable if you want more details.”

<more soda>

“I also found a paper, ‘The Silurian Hypothesis,’ that took a more technical approach. Their big library research project pulled results from scores of geologic isotope analysis and fossil survey reports looking for ancient times that resemble Earth’s sudden change since the start of the Industrial Age — climate, species declines, whatever. They found about a dozen, but as they said, ‘the known unique markers might not be indicative, while the (perhaps) more expected markers are not sufficient.’ In other words, my Crazy Theory might be crazy. Or maybe not.”

~~ Rich Olcott

Myopic Astronomy

Cathleen goes into full-on professor mode. “OK folks, settle down for the final portion of “IR, Spitzer and The Universe,” our memorial symposium for the Spitzer Space Telescope which NASA retired on January 30. Jim’s brought us up to speed about what infra-red is and how we work with it. Newt’s given us background on the Spitzer and its fellow Great Observatories. Now it’s my turn to show some of what Astronomy has learned from Spitzer. Thousands of papers have been published from Spitzer data so I’ll just skim a few highlights, from the Solar System, the Milky Way, and the cosmological distance.”

“Ah, Chinese landscape perspective,” murmurs the maybe-an-Art-major.

“Care to expand on that?” Cathleen’s a seasoned teacher, knows how to maintain audience engagement by accepting interruptions and then using them to further her her own presentation.

“You show detail views of the foreground, the middle distance and the far distance, maybe with clouds or something separating them to emphasize the in‑between gaps.”

“Yes, that’s my plan. Astronomically, the foreground would be the asteroids that come closer to the Earth than the Moon does. Typically they reflect about as much light as charcoal so our visible-light telescopes mostly can’t find them. But even though asteroids are as cold as interplanetary space that’s still above absolute zero. The objects glow with infra-red light that Spitzer was designed to see. It found hundreds of Near-Earth Objects as small as 6 meters across. That data helped spark disaster movies and even official conversations about defending us from asteroid collisions.”

<A clique in the back of the room> “Hoo-ahh, Space Force!

Some interruptions she doesn’t accept. “Pipe down back there! Right, so further out in the Solar System, Spitzer‘s ability to detect glowing dust was key to discovering a weird new ring around Saturn. Thanks to centuries of visible‑range telescope work, everyone knows the picture of Saturn and its ring system. The rings together form an annulus, an extremely thin circular disk with a big round hole in the middle. The annulus is bright because it’s mostly made of ice particles. The annulus rotates to match Saturn’s spin. The planet’s rotational axis and the annulus are both tilted by about 27° relative to Saturn’s orbit. None of that applies to what Spitzer found.”

Vinnie’s voice rings out. “It’s made of dust instead of ice, right ?”

Cathleen recognizes that voice. “Good shot, Vinnie, but the differences don’t stop there. The dust ring is less a disk than a doughnut, about 200 thousand times thicker than the icy rings and about 125 times wider than the outermost ice ring. But the weirdest part is that the doughnut rotates opposite to the planet and it’s in Saturn’s orbital plane, not tilted to it. It’s like the formation’s only accidentally related to Saturn. In fact, we believe that the doughnut and its companion moon Phoebe came late to Saturn from somewhere else.”

She takes a moment for a sip of coffee. “Now for the middle distance, which for our purpose is the stars of the Milky Way. Spitzer snared a few headliners out there, like TRAPPIST-1, that star with seven planets going around it. Visible-range brightness monitoring suggested there was a solar system there but Spitzer actually detected light from individual planets. Then there’s Tabby’s Star with its weird dimming patterns. Spitzer tracked the star’s infra‑red radiance while NASA’s Swift Observatory tracked the star’s emissions in the ultra‑violet range. The dimming percentages didn’t match, which ruled out darkening due to something opaque like an alien construction project. Thanks to Spitzer we’re pretty sure the variation’s just patchy dust clouds.”

Spitzer view of the Trifid Nebula
Credit: NASA/JPL-Caltech/J. Rho (SSC/Caltech)

<from the crowd in general> “Awww.”

“I know, right? Anyway, Spitzer‘s real specialty is inspecting warm dust, so no surprise, it found lots of baby stars embedded in their dusty matrix. Here’s an example. This image contains 30 massive stars and about 120 smaller ones. Each one has grown by eating the dust in its immediate vicinity and having lit up it’s now blowing a bubble in the adjacent dust.” <suddenly her cellphone rings> “Oh, sorry, this is a call I’ve got to take. Talk among yourselves, I’ll be right back.”

~~ Rich Olcott

A Mole’s Tale

Chilly days are always good for a family trip to the science museum. Sis is interested in the newly unearthed dinosaur bones, but Teena streaks for the Space Sciences gallery. “Look, Uncle Sy, it’s a Mars rover. No, wait — it doesn’t have wheels — it’s a lander!”

Artist’s depiction of InSight — credit NASA/JPL-Caltech

A nearby museum docent catches that. “Good observing, young lady. You’re right, it’s NASA’s Insight lander. It touched down on Mars last Thanksgiving Day. While you were having turkey and dressing, we were having a party over here.”

“Is this the real one? How’d you get it back?”

“No, it’s just a model, but it’s full-size, 19½ feet across. We’re never going to get the real one back — those little bitty landing rockets you see around the electronics compartment are too small to get it off the planet.”

“Tronics compartment? You mean the pretty gold box underneath the flat part? Why’d they make it gold?”

“That gold is just the outside layer of a dozen layers of Mylar insulation. It helped to keep the computers in there cool during the super-hot minutes when the lander was coming down through Mars atmosphere. The insulation also keeps the electronics warm during the cold martian night. A thin gold coating on the outermost layer reflects the bad part of sunlight that would crumble the Mylar.”

“Computers like Mommie’s laptop? I don’t see any screens.”

“They don’t need any. No-one’s on Mars to look at them. The instructions all come in from Earth by radio.”

Sis is getting into it. “Look, Sweetie, the platform in the middle’s about the same size as our kitchen table.”

“Yeah, but it’s got butterfly wings. A flying kitchen table, whee!”

“Those wings are solar panels. They turn sunlight into the electricity Insight needs to run things and keep warm. They make enough power for three households here on Earth.”

“What’s the cake box about?”

SEIS —
Seismic Experiment for Interior Structure

“Cake box?”

“Yeah, down there on the floor.”

“Ah. That’s for … have you ever experienced an earthquake?”

“Yes! Suddenly all the dishes in the cupboard went BANG! It was weird but then everything was fine.”

“I’m glad. OK, an earthquake is when vibrations travel through the Earth. Vibrations can happen on Mars, too, but they’re called…”

“Marsquakes! Ha, that’s funny!”

“Mm-hm. Well, that ‘cake box’ is something called a seismometer. It’s an extremely sensitive microphone that listens for even the faintest vibrations. When scientists were testing the real seismometer in Boulder, Colorado it recorded a steady pulse … pulse … pulse … that they finally traced back to ocean waves striking the coast of California, 1200 miles away. Insight took it to Mars and now it’s listening for marsquakes. It’s already heard a couple dozen. They’ve given the scientists lots of new information about Mars’ crust and insides.”

“Like an X-ray?”

“Just like that. We’ll be able to tell if the planet’s middle is molten–“

“Hot lava! Hot lava!”

“Maybe. Earth has a lot of underground lava, but we think that Mars has cooled off and possibly doesn’t have any. That other device on the ground is supposed to help find out.”

HP3 — Heat Flow and
Physical Properties Package

“It looks like The Little Engine That Could.”

“It does, a little, but this one maybe can’t. We’re still waiting to see. That chimney-looking part held The Mole, a big hollow spike with something like a thermometer at its pointy tip. Inside The Mole there’s a hammer arrangement. The idea was that the hammer would bang The Mole 15 feet into the ground so we could take the planet’s temperature.”

“Did the banging work?”

“It started to, but The Mole got stuck only a foot down. The engineers have been working and working, trying different ways to get it down where we want it but so far it’s still stuck.”

“Aww, poor Mole.”

TWINS – Temperature
and Wind for InSight

“Yes. But there’s another neat instrument up on the platform. Here, I’ll shine my laser pointer at it. See the grey thingy?”

“Uh-huh.”

“That’s a weather station for temperature and wind. You can check its readings on the internet. Here, my phone’s browser’s already set to mars.nasa.gov/insight/weather. Can you read the high and low temperatures?”

“Way below zero! Wow, Mars is chilly! I’d need a nice, warm spacesuit there.”

“For sure.”

~~ Rich Olcott

Where would you put it all?

Vinnie’s a big guy but he’s good at fading into the background. I hadn’t even noticed him standing in the back corner of Cathleen’s impromptu seminar room until he spoke up. “That’s a great theory, Professor, but I wanna see numbers for it.”

“Which part of it don’t you like, Vinnie?”

“You made it seem so easy for all those little sea thingies to scrub the carbon dioxide out of Earth’s early atmosphere and just leave the nitrogen and oxygen behind. I mean, that’d be a lot of CO2. Where’d they put it all?”

“That’s a reasonable question, Vinnie. Lenore, could you put your Chemistry background to work on it for us?”

“Oh, this’ll be fun, but I don’t want to do it in my head. Mr Moire, could you fire up Old Reliable for the calculations?”

“No problem. OK, what do you want to calculate?”

“Here’s my plan. Rather than work with the number of tons of carbon in the whole atmosphere, I’ll just look at the sky-high column of air sitting on a square meter of Earth’s surface. We’ll figure out how many moles of CO2 would have been in that column back then and then work on how thick a layer of carbon stuff it would make on the surface. Does that sound like a good attack, Professor?”

“Sure, but I see a couple of puzzled looks in the class. You’d better say something about moles first.”

“Hey, I know about moles. Sy and me talked about ’em when he was on that SI kick. They’re like a super dozen, right, Sy?”

“Right, Vinnie. A mole of anything is 6.02×1023 of that thing. Eggs, atoms, gas molecules, even stars if that’d be useful.”

“Back to my plan. First thing is the CO2 was in that column back when. Maria, your chart showed that Venus’ atmospheric pressure is 100 times ours and Mars’ is 1/100 ours and each of them is nearly pure CO2, right? So I’m going to assume that Earth’s atmosphere was what we have now plus a dose of CO2 that’s the geometric mean of Venus and Mars. OK, Professor?”

“That’d be a good starting point, Lenore.”

“Good. Now we need the mass of that CO2, which we can get from the weight of the column, which we can get from the air pressure, which is what?”

Every car buff in the room, in chorus — “14½ pounds per square inch.”

“I need that in kilograms per square meter.”

“Strictly speaking, pressure’s in newtons per square meter. There’s a difference between weight and force, but for this analysis we can ignore that. Keep going, Lenore.”

“Thanks, Professor. Sy?”

“Old Reliable says 10194 kg/m².”

“So we’ve got like ten-thousand kilograms of CO2 in that really tall meter-square column of ancient air. Now divide that by, um, 44 to get the number of moles of CO2. No, wait, then multiply by 1000 because we’ve got kilograms and it’s 44 grams per mole for CO2.”

“232 thousand moles. Still sounds like a lot.”

“I’m not done. Now we take that carbon and turn it into coal which is solid carbon mostly. One mole of carbon from each mole of CO2. Take the 232 thousand moles, multiply by 12 grams, no make that 0.012 kilogram per mole –“

“2786 kilograms”

“Right. Density of coal is about 2 grams per cc or … 2000 kilograms per cubic meter. So. Divide the kilograms by 2000 to get cubic meters.”

“1.39 meters stacked on that square-meter base.”

“About what I guessed it’d be. Vinnie, if Earth once had a carbon-heavy atmosphere log-halfway between Venus and Mars, and if the sea-plankton reduced all its CO2 down to coal, it’d make a layer all over the planet not quite as tall as I am. If it was chalk it’d be thicker because of the additional calcium and oxygen atoms. A petroleum layer would be thicker, too, with the hydrogens and all, but still.”

Jeremy’s nodding vigorously. “Yeah. We’ve dug up some of the coal and oil and put it back into the atmosphere, but there’s mountains of limestone all over the place.”

Cathleen’s gathering up her papers. “Add in the ocean-bottom carbonate ooze that plate tectonics has conveyor-belted down beneath the continents over the eons. Plenty of room, Vinnie, plenty of room.”

~~ Rich Olcott

The Moon And Chalk

Cathleen’s talking faster near the end of the class. “OK, we’ve seen how Venus, Earth and Mars all formed in the same region of the protosolar disk and have similar overall compositions. We’ve accounted for differences in their trace gasses. So how come Earth’s nitrogen-oxygen atmosphere is so different from the CO2-nitrogen environments on Venus and Mars? Let’s brainstorm — shout out non-atmospheric ways that Earth is unique. I’ll record your list on Al’s whiteboard.”

“Oceans!”

“Plate tectonics!”

“Photosynthesis!”

“Limestone!”

“The Moon!”

“Wombats!” (That suggestion gets a glare from Cathleen. She doesn’t write it down.)

“Goldilocks zone!”

“Magnetic field!”

“People!”

She registers the last one but puts parentheses around it. “This one’s literally a quickie — real-world proof that human activity affects the atmosphere. Since the 1900s gaseous halogen-carbon compounds have seen wide use as refrigerants and solvents. Lab-work shows that these halocarbons catalyze conversion of ozone to molecular oxygen. In the 1970s satellite data showed a steady decrease in the upper-atmosphere ozone that blocks dangerous solar UV light from reaching us on Earth’s surface. A 1987 international pact banned most halocarbon production. Since then we’ve seen upper-level ozone concentrations gradually recovering. That shows that things we do in quantity have an impact.”

“How about carbon dioxide and methane?”

“That’s a whole ‘nother topic we’ll get to some other day. Right now I want to stay on the Mars-Venus-Earth track. Every item on our list has been cited as a possible contributor to Earth’s atmospheric specialness. Which ones link together and how?”

Adopted from image by Immanuel Giel, CC BY-SA 3.0

Astronomer-in-training Jim volunteers. “The Moon has to come first. Moon-rock isotope data strongly implies it condensed from debris thrown out by a huge interplanetary collision that ripped away a lot of what was then Earth’s crust. Among other things that explains why the Moon’s density is in the range for silicates — only 60% of Earth’s density — and maybe even why Earth is more dense than Venus. Such a violent event would have boiled off whatever atmosphere we had at the time, so no surprise the atmosphere we have now doesn’t match our neighbors.”

Astrophysicist-in-training Newt Barnes takes it from there. “That could also account for why only Earth has plate tectonics. I ran the numbers once to see how the Moon’s volume matches up with the 70% of Earth’s surface that’s ocean. Assuming meteor impacts grew the Moon by 10% after it formed, I divided 90% of the Moon’s present volume by 70% of Earth’s surface area and got a depth of 28 miles. That’s nicely within the accepted 20-30 mile range for depth of Earth’s continental crust. It sure looks like our continental plates are what’s left of the Earth’s original crust, floating about on top of the metallic magma that Earth held onto.”

Jeremy gets excited. “And the oceans filled up what the continents couldn’t spread over.”

“That’s the general idea.”

Al’s not letting go. “But why does Earth have so much water and why is it the only one of the three with a substantial magnetic field?”

Cathleen breaks in. “The geologists are still arguing about whether Earth’s surface water was delivered by billions of incoming meteorites or was expelled from deep subterranean sources. Everyone agrees, though, that our water is liquid because we’re in the Goldilocks zone. The water didn’t steam away as it probably did on Venus, or freeze below the surface as it may have on Mars. Why the magnetic field? That’s another ‘we’re still arguing‘ issue, but we do know that magnetic fields protect Earth and only Earth from incoming solar wind.”

“So we’re down to photosynthesis and … limestone?”

“Photosynthesis was critical. Somewhere around two billion years ago, Earth’s sea-borne life-forms developed a metabolic pathway that converted CO2 to oxygen. They’ve been running that engine ever since. If Earth ever did have CO2 like Venus has, green things ate most of it. Some of the oxygen went to oxidizing iron but a lot was left over for animals to breathe.”

“But what happened to the carbon? Wouldn’t life’s molecules just become CO2 again?”

“Life captures carbon and buries it. Chalky limestone, for instance — it’s calcium carbonate formed from plankton shells.”

Jim grins. “We owe it all to the Moon.”

~~ Rich Olcott

Traces of Disparity

Cathleen’s an experienced teacher — she knows when off-topic class discussion is a good thing, and when to get back to the lesson plan. “My challenge question remains — why isn’t Earth’s atmosphere some average of the Mars and Venus ones? Thanks to Jeremy and Newt and Lenore we have reason to expect the planets to resemble each other, but in fact their atmospheres don’t. Maria, tell us what you’ve found about how Earth compares with the others.”

“Yes, Profesora. I found numbers for many of the gasses on each planet and put them into this chart. One thing Earth is right in the middle, most things not.”

“That’s a complicated chart. Read it out to us.”

“Of course. I had to make the vertical scales logarithmic to get the big numbers and small numbers on the same chart. First is the pressure which is the black dotted line. Venus pressure at the surface is nearly 100 times ours but Mars pressure is a bit less than 1/100th of ours. Does that count as Earth being in the middle?”

“That’d be a geometric average. It could be significant, we’ll see. Go on.”

“The gas that is almost the same everywhere is helium, the grey diamonds. That surprised me, because I thought the giant planets got all of that.”

Al’s been listening in. Nothing else going on in his coffee shop, I guess. “I’ll bet most of that helium came from radioactive rocks, not from space. Alpha particles, right, Cathleen?”

Cathleen takes unexpected interruptions in stride. “Bad bet, Al. Uranium and other heavy elements do emit alphas which pick up electrons to become helium atoms. You probably remembered Cleve and Langlet, who first isolated helium from uranium ore. However, the major source of atmospheric alphas is the solar wind. Solar wind interception and atmosphere mass are both proportional to planetary surface area so a constant concentration like this is reasonable. Continue, Maria.”

“The major gasses follow a pattern — about the same fractions on Venus and Mars but much higher or lower than on Earth. Look at carbon dioxide, nitrogen, even oxygen.”

Astronomer-in-training Jim has been doing some mental arithmetic. “Our atmosphere is 100 times denser than on Mars, and Venus is another factor of 100 beyond that. That’s a factor of 104 between them — for every molecule of CO2 on Mars there’s 10,000 on Venus. Oh, but Venus has four times Mars’ surface area so make that 40,000.”

“Good points, both of you. Jim’s approximation leads into something we can learn from Maria’s trace gas numbers. Why do you suppose the concentration of SO2 is about the same for Earth and Mars but 100 times higher on Venus, but the reverse is true for argon? Where do they each come from?”

Jeremy finally has something he can contribute. “Volcanoes! They told us in Geology class that most of our SO2 comes from volcanoes. Before the Industrial Revolution, I mean, when we started burning high-sulfur coal and fuel oils and made things worse. Venus has to be the same. Except for the industry, of course.”

“Probably correct, Jeremy. From radar mapping of Venus we know that it has over 150 large volcanoes. We don’t know how many of them are active, but the Venus Express spacecraft sent back evidence of active vulcanism. In fact, Venus’ SO2 score would probably be even higher if much of its production didn’t oxidize to SO3. That combines with water to form the clouds of sulfuric acid that hide the planet’s surface and reflect sunlight so brightly.”

Maria’s hand is up again. “I don’t understand argon’s purple diamonds, profesora. I know it’s one of the inert gasses so it doesn’t have much chemistry and can’t react into a mineral like CO2 and SO2 can. Shouldn’t argon be about the same on all three planets, like helium?”

“Mm-hm, argon does have a simple chemistry, but its radiochemistry isn’t so simple. Nearly 100% of natural argon is the argon-40 isotope created by radioactive decay of potassium-40. Potassium is tied up in the rocks, so the atmospheric load of argon-40 depends on rocky surface erosion. Not much erosion, not much argon.”

Al’s on tenterhooks. “All this is nice, but you still haven’t said why Earth’s atmosphere is so different.”

~~ Rich Olcott