Science In My Fiction

Mars. There’s something about the Red Planet that gets people excited. Sure, part of it may be that it is the most Earth-like planet in the solar system (except for Earth…) but even more powerful are the stories that are told about it. Mars has been the subject of myths since before recorded history, and more recently has been the setting or inspiration for reams of science fiction.

For those of us who like a little science in our fiction, the good news is that in the last decade our understanding of the Red Planet has grown by leaps and bounds thanks to a whole armada of space probes: Mars Global Surveyor, Mars Odyssey, Mars Pathfinder, Mars Express, the two Mars Exploration Rovers, Phoenix, and Mars Reconnaissance Orbiter.

All of these missions came after the publication of the classic hard sci-fi masterpiece “Red Mars” by Kim Stanley Robinson, so I thought it would be interesting to take a look at how Red Mars holds up.

The short answer is: pretty well! Kim Stanley Robinson did a phenomenal amount of research for the book, and the Mars that he describes is still remarkably accurate. The book is a tome, so I can’t go through and critique every bit of Mars science in it, so I will focus on a few key sections.

First, let’s look at the beginning of Part Three: The Crucible. (If you’d like to follow along, a PDF version of the book is available here, legally, for free) This section begins with a description of how Mars formed, and how it acquired its geography (areography?). The language takes some poetic license, but is generally accurate: Mars did indeed form along with the rest of the solar system about 4.5 billion years ago (I’ll forgive Robinson for rounding up to 5) from the gradual accretion of planetesimals, and it did have a short-lived magnetic field.

What Robinson didn’t know was that the evidence of that magnetic field is still preserved in the ancient rocks of the southern hemisphere! The magnetization was obliterated by the giant impacts Hellas and Argyre, but elsewhere in the southern highlands there are broad bands of opposing magnetic fields. These are similar to the alternating bands of magnetization preserved near tectonic spreading centers on the earth caused by the switching of the Earth’s magnetic field, but on a much larger scale. Some scientists have used this similarity to argue in favor of plate tectonics on early Mars, but there’s not a lot of other evidence for plate tectonics so this hypothesis isn’t very popular these days.

Robinson is also correct that the huge Tharsis bulge and its towering volcanoes probably are caused by convection in the mantle, and that a leading theory for the formation of the northern lowlands is that they are a single gigantic impact basin. This giant impact theory has been making a comeback lately. By using careful measurements of the martian gravity, scientists have been able to figure out how thick the crust is, and effectively “subtract” the Tharsis bulge. What’s left in the northern hemisphere is a gargantuan elliptical crater, 10,000 km by 8,500 km.

Oh how Robinson must wish he had this topographic map of Mars when writing! Blue is low, red and white are high. Tharsis is the huge high elevation area dotted with volcanoes west of the giant canyons of Valles Marineris.

The idea of Mars’ moons Phobos and Deimos as ejecta  from a similar giant impact is still alive and kicking. Mars Express has found evidence of clay minerals on Phobos, which only form when water is available. This, combined with the moon’s low density suggest that it is probably a piece of the ancient martian crust rather than a captured asteroid.

The intro to Part Three is also pretty accurate in its description of water on Mars. We now know for sure that there is water on Mars, and that there is likely a lot of ice beneath the surface. It’s not necessarily all in the form of pure-ice lenses like Robinson describes, but it’s there, and there seem to be lenses at least in some places, like the Phoenix landing site.

Finally, he’s spot on in his description of life on Mars (or the lack thereof) at the end of the intro to Part Three. Even the references to sulfur and clays and hot springs are accurate! Mars Express and Mars Reconnaissance Orbiter have both found evidence of clays and sulfates in the ancient rocks all over mars, and the Spirit rover has dug up sulfate- and silica- rich soil interpreted as the result of hydrothermal activity. But so far, no evidence for life. All the claims of life in Martian meteorites have been met with plausible inorganic explanations, and Phoenix has discovered perchlorates in the martian soil – powerful oxidizers that help explain the confusing results of the Viking landers’ life detection experiments.

Let’s fast forward a bit to page 131 of the pdf. Some of the colonists are on a road trip to the north polar cap to set up some automated ice-mining. Setting aside the implausibility of being able to drive halfway across the planet without any trouble, there is a statement made in passing here that really does reflect a fundamental change in our understanding of Mars.

“The rocks you see here come from late meteor action. The total accumulation of loose rock from meteor strikes is much greater than what we can see, that’s what gardened regolith is. And the regolith is a kilometer deep.”

This is an idea that was carried over to Mars by scientists who cut their teeth studying the moon. It’s certainly true for much of the moon, where there are few geologic processes other than volcanism and impacts. But one of the most significant things that has been learned about Mars since Red Mars was written is that it is not just a big red version of the moon. With the first really high resolution images of Mars returned by the Mars Orbital Camera on Mars Global Surveyor, and the spectacular even-higher-resolution images that continue to stream down from HiRISE on MRO, we can start to see Mars as it really is. Yes, there are lots of craters, and the regolith is made of ejecta from eons of impacts, but it’s not ejecta all the way down like it is on the moon. Mars has sedimentary rocks, and lots of them. Volcanic ash lofted thousands of kilometers by the martian atmosphere and deposited in blanketing layers, sand seas cemented in place by hydrated minerals, sediment settling through the icy waters of short-lived lakes. All of these combine to form thick sequences of layered rocks. Sure, there are also craters interbedded with the other layers, but cratering is just one of many processes at work on Mars.

An illustration of the idea of the martian crust as a "cratered volume" rather than just a bunch of megabreccia. Here, craters are interbedded with various layered rocks, going down many kilometers. (image from Malin and Edgett, 2001)

Even more amazing is how much the landscape has changed. There is evidence that huge swaths of the planet were once buried and have been exhumed by billions of years of erosion. In Gale Crater, one of the potential landing sites for the next Mars rover, there is a 6km high mountain of sedimentary rock that is taller than the rim of the crater it sits in. How far did those rocks once extend? In some places, erosion has partially uncovered craters that look for all the world like they should be freshly formed. Except that they are half buried under a billion years of rock.

It is difficult, even for those of us who study Mars, to look at the surface as it is now and remember that we are just seeing the upper layer of an intricate intermingling of processes, and that kilometers of rock may have been stripped away from above the present surface. It’s amazing what four billion years of erosion can do to a planet. Even though Robinson isn’t quite right when he writes that the regolith goes down a kilometer, he was right about the most fundamental difference between Earth and Mars:

“It’s billions of years. That’s the difference between here and Earth, the age of the land goes from millions of years to billions. It’s such a big difference it’s hard to imagine.”

Later in the same section of the book, Robinson reveals another case where the information available when he was writing pales compared to what we have now:

“Ann was crouching, a scoop of sand in her palm.

“What’s it made of?” Nadia asked.

“Dark solid mineral particles.”

Nadia snorted. “I could have told you that.”

“Not before we got here you couldn’t. It might have been fines aggregated with salts. But it’s bits of rock instead.”

“Why so dark?”

“Volcanic. On Earth sand is mostly quartz, you see, because there’s a lot of granite there. But Mars doesn’t have much granite. These grains are probably volcanic silicates. Obsidian, flint, some garnet. Beautiful, isn’t it?”

I thought this was quite telling because these days we have a very good idea of what the sand on Mars is made of, thanks to the spectrometers on Mars Express and MRO, and the results of the MER rovers. The nice thing about sand dunes is that they are self-cleaning: the saltation of the sand grains knocks the dust off of them, so the dunes on Mars often have nice clean spectra revealing a basaltic composition, with lots of minerals containing iron and magnesium. Robinson shows his earthly biases when he lists things like obsidian, flint and garnet – these all have much higher silica and aluminum than basalts, a good sign that the rock containing them has been recycled by plate tectonics. On Mars, just about everything is basaltic, or the result of weathering basalt. The same spectrometers that found the composition of sand on Mars have also found hundreds of examples of minerals formed by the interaction of water with basaltic rocks, but there are not many places where more processed, high-Si and high-Al rocks are found.

Jumping forward again to page 241 of the pdf, there are some interesting comments about glaciers and oceans on Mars:

“The glacial theory, however, and the oceanic model of which it was part, had always been more persistent than most. First, because almost every model of the planet’s formation indicated that there should have been a lot of water outgassing, and it had to have gone somewhere. And second, John thought, because there were a lot of people who would be comforted if the oceanic model were true; they would feel less uneasy about the morality of terraforming.”

We aren’t too concerned about the morality of terraforming yet, but the rest of this excerpt is pretty spot-on. The ocean hypothesis for Mars still lives on, partially because of new discoveries, but partially because people want it to be true. One interesting recent result took a look at all the features on Mars that might be deltas formed by rivers dumping their sediment into a standing body of water. Many of these are in craters, so you only need to invoke enough water to fill the crater, but there are some that empty into the northern lowlands, and they are all at about the same elevation. Likewise, the density of drainage channels on Mars has been mapped and it shows a similar cutoff with elevation. Are these results evidence of a northern ocean? Maybe, maybe not.

A map of the density of drainage channels on Mars, in relation to a hypothetical northern ocean. Image credit: Wei Luo/Northern Illinois University/PA Wire

As for glaciers, this is another area that has made a lot of progress since Red mars was published. Mars Express and MRO both carry ground-penetrating radar instruments designed to look for ice on the surface of Mars. These have given some spectacular cross-section views of the polar caps, but maybe even more important is the discovery that there are huge lobate masses of ice – some might call them glaciers – buried under thin layers of rocky debris on Mars. I’m a little surprised that Robinson did not mention these because they had been seen even before MOC and HiRISE sent back high-resolution photos. The radar results just confirmed that these lobate features were mostly ice rather than mostly rock.

A map of glacial ice (blue) discovered in the mid-latitudes of mars by ground-penetrating radar. The lobes of ice are buried under a thin layer of soil which protects it from sublimating away.

Overall, the science in Red Mars is remarkably good even today. If you want to get a good basic understanding of Mars science (or if you want to read an epic story of colonization, human drama, etc.) Red Mars is a great place to start. Still, we know a lot more about some things than we did when the book was written. We know that Mars has honest-to-goodness sedimentary rocks and a stratigraphic record that is more complex than just craters and volcanoes. We know a phenomenal amount about the composition of the surface thanks to orbiting spectrometers and the Pathfinder, MER and Phoenix landers. And we know that there is ice, not just at the poles, not just beneath the surface in the arctic, but in vast buried glaciers even in the low latitudes.

With all that we do know, it’s striking to me how many of the big questions about Mars that Robinson mentions in the book are still open to debate today. Did Mars have an ocean? Maybe. Was it ever warm and wet? Maybe. Is the northern hemisphere a giant crater? Maybe.

Is there life on Mars? Maybe. Maybe not. Maybe not yet.

There’s no better way to fire up my imagination than to introduce me to a cool new place, real or imagined. Something about imagining what it’s like Elsewhere just captivates me. That’s a big part of why I like speculative fiction: fantasy and science fiction are full of exotic new worlds to explore. But it’s also a big part of why I study planets for a living. There are plenty of actual exotic new worlds to explore out there in the universe, and I thought I’d share some of my favorites in the hopes of sparking your imagination too.

I’ll start here on Earth. You might think earth is a bit, well, mundane, but there are some really weird places hidden away even on our familiar home planet that are just begging to be the setting for some fiction. Take, for instance, la Cueva de los Cristales (the Cave of Crystals) in Mexico. The cave is brutally hot and humid, but it is filled with translucent crystals the size of tree trunks, forming a breathtaking natural cathedral.

Another hellish but spectacular place on earth is the Kawah Ijen sulfur mine in Indonesia. I only recently learned about this place from a feature on The Big Picture photo blog, which showed some surreal photos of this volcanic mine where oozing molten sulfur burns with a blue flame and the air is filled with acidic gases. And of course, the ultimate alien locale on our own planet is the deep sea, where entire ecosystems are still being discovered, with creatures more imaginative and terrifying than any fiction.

Burning molten sulfur in the Kawah Ijen sulfur mine.

But really, that stuff is pretty tame compared to the rest of the universe, so let’s take a look at some other awesome places. We’ll start off with Mars. What’s so special about Mars? It’s just a big desert right? Well it has a few claims to fame. You may have heard that it boasts the tallest volcano in the solar system – Olympus Mons – which towers almost three times as high as Mount Everest. Mars is also home to Valles Marineris, the largest canyon in the solar system, which stretches for 4000 km and is 200 km across at its widest point. Ok, so it has a couple planetary tourist traps. To get to the really strange stuff you have to head south. The south polar residual cap on Mars is made of frozen carbon dioxide – a.k.a. dry ice – and it is slowly disappearing. As the cap sublimates, it forms some really bizarre features. Take a look at this picture of the “swiss cheese terrain”:

HiRISE image of the "swiss cheese terrain" of the martian south polar ice cap.

Believe it or not, the smooth, fractured areas in this picture are the high ground (the lighting is from the lower right). The rounded pits are formed as the dry ice turns to gas. Even cooler are the south polar “spiders” – dark splotches that can appear on the ice in a matter of days. One of the leading theories for how these form is that the ice acts like a greenhouse, allowing sunlight to pass through it until it hits a darker layer. As that layer absorbs sunlight, it warms up, vaporizing the ice and creating a high-pressure pocket of gas that erupts, dumping dust onto the surface. How about some fiction set on an unstable landscape of sublimating carbon dioxide, where every step could set off a violent geyser or collapse the roof of an icy greenhouse?

Not impressed by swiss cheese and spiders? Then let’s head out to the icy moons of the outer solar system! We’ll bypass Io’s sulfur-laden volcanoes and Europa’s icy ocean because those are pretty well known in sci-fi. Instead I’d like to focus on two of Saturn’s moons. The first is Iapetus, a familiar name to anyone who has read the book 2001: A Space Odyssey. (In the movie the obelisk was re-located to Europa because they had trouble making convincing-looking rings for Saturn) Arthur C. Clarke picked a great location in which to hide an alien artifact though, because Iapetus is decidedly weird and artificial-looking. First of all, it is two-faced. One hemisphere is black as coal, while the other is as white as snow. And it’s not a smooth transition between the two either: recent photos of the dividing line show splotches of pure black and pure white. It’s like looking at a close-up of a dalmation. The leading theory for this abrupt color change is that Iapetus sweeps up debris blasted off the moon Phoebe. Since Iapetus is tidally locked with the same hemisphere facing Saturn at all times, this material always hits the same hemisphere, causing it to darken. Once it darkens a little bit the sun takes over, heating up the darkened areas and causing surface ice there to sublimate away and condense on the brighter areas. Over time this darkens the dark spots and brightens the bright spots.

The dark hemisphere of Iapetus, showing the strange equatorial ridge.

The other weird thing about Iapetus is that it has a 13 km high ridge of mountains running for 1300 km precisely along its equator, and nobody really knows why it’s there! The leading theory is that Iapetus used to rotate much faster and so was fatter at its equator. It has since cooled (and therefore become more rigid) and also has slowed its spin. The ridge might have been formed as Iapetus tried to change shape in response to its new, slower rotation rate. Still, to anyone with a science-fictional bent, that equatorial ridge brings to mind all sorts of more exotic possibilities. As the saying goes, “That’s no moon…”

Titan, another one of Saturn’s moons, is even more unusual than Iapetus. Titan is strange because it is the only moon with a thick atmosphere. In fact, its atmospheric pressure is greater than the pressure here on Earth despite its lower gravity! Earth is the only other place in the solar system with a significant nitrogen atmosphere. But the similarities with Earth don’t stop there. The Cassini mission has also found river beds, lakes, seas and thunderstorms on Titan! That would be interesting enough, but the really wild thing is that the surface temperature of Titan is -180 degrees C (-292 F)! At that temperature, water is frozen so hard you can basically think of it as a mineral. It turns out that instead of a water cycle like the Earth, Titan has a hydrocarbon cycle. Methane and ethane take the place of water, condensing to form violent thunderstorms which rain down forming rivers, lakes and seas. The surface is obscured by a smog of heavier hydrocarbons that also gradually settle out of the atmosphere forming great deserts of coal-like sand. There is 1000 times more hydrocarbon locked up as sand on Titan than there is in all the coal on Earth, not to mention all the liquid natural gas that fills Titan’s lakes and seas! What I love about Titan is how it looks so familiar but is so bizarrely different at the same time.  Only nature could be creative enough to come up with an icy moon literally drenched in fuel! I’m just waiting for the first interplanetary expedition led by Exxon and BP.

A false-color radar view of the seas and lakes of methane and ethane near Titan's north pole.

But that’s just the tip of the iceberg. We still haven’t even left the solar system, but to date there are 500 known exoplanets orbiting 421 stars, and new planets are being discovered all the time. If the most exotic places in our own solar system don’t seem science fictional enough for you, then just consider some of the awesome exoplanets that have been discovered:

First of all, we have the “hot jupiters” – gas giants that are so close to their stars they orbit in a matter of hours or days rather than decades. The extreme temperatures drive some pretty crazy weather: Astronomers have detected winds blowing  10,000 km per hour on the hot Jupiter planet HD209458b! Even more mind-blowing is that on some of these planets, instead of clouds made of water and ammonia, there are clouds made of silicate minerals or iron!

Rocky planets close enough to their stars might also have some pretty exotic clouds. Planets orbiting close to their stars are “tidally locked” just like our moon, so the same side always faces the star. That means that on a planet like COROT-7b, a possibly rocky planet with a mass about five times that of earth, the sunlit side gets absurdly hot. Estimates put the sub-solar temperature for COROT-7b at 2600 K (4220 F), which is hot enough to vaporize rock and metal, giving the planet clouds of glowing yellow sodium gas and silicate minerals. If you thought methane rain on Titan was weird, stay clear of the olivine sleet on COROT 7b! Obviously these places wouldn’t be very pleasant places for humans to visit, but the great thing about science fiction is that you can bend some rules. Maybe the higher temperatures make silicon-based life more plausible. Or maybe future post-humans scoff in the face of mere high temperatures and visit these planets to mine the clouds.

Artist's rendition of a hot jupiter, complete with incandescent clouds.

I’ve always been fascinated by the idea of these tidally locked worlds because even though the day side can be hellishly hot, the night side temperatures would plummet to nearly absolute zero, and somewhere on the terminator (the transition between day and night) the temperature would be nice and comfortable. But that’s only if the planet has no atmosphere. Things get a lot more complicated and more interesting if there is a way to convect heat from the hot side to the cold side.  A couple months ago I heard a very cool talk by Ray Peirrehumbert about the climate on the possible earth-like planet Gliese 581g. (As a side note, the Gliese 581 system, with at least six planets, is just crying out to be the setting for some sci-fi!) He described a whole range of possible climates for this tidally-locked world, the coolest and most-habitable of which was the “eyeball earth” scenario. In this case, the planet is mostly ocean with an atmosphere not all that different from our own. Under the sub-solar point the dark open water absorbs enough energy to stay liquid at a cozy 37 degrees C, but as you go farther away, temperatures drop and the ocean freezes. The result is an “iris” of warm open water on an otherwise icy world. You can tweak the amount of greenhouse gas in the atmosphere to vary the size of the open water pool. The only downside is that if the eyeball earth does somehow ice over completely, the ice reflects enough sunlight to prevent the water pool from opening up again. I, for one, would love to read the story of a civilization on Gliese 581g struggling to prevent their world from freezing over. Instead of Martians struggling to survive by building canals, you could have Glieseians building giant CO2 factories!

From Pierrehumbert's paper on the possible climate of Gliese581g

You can get some even weirder planets if you change their composition. For example, the planet WASP 12b is thought to be a “carbon planet”, which as the name suggests, is unusually rich in carbon. WASP 12b is a gas giant, but a carbon-rich rocky planet would be a very interesting place. Instead of normal rocks, you would have mountains made of graphite, diamonds and asphalt. Or if a carbon planet doesn’t float your boat, what about an earth-sized planet made mostly of water? (It would, of course, have to be named Sea World) With oceans hundreds of kilometers deep, the pressures at the bottom would grow so high that exotic forms of ice would form even at high temperatures. Considering the alien life in our own oceans, just imagine what might live in the depths of Sea World!

Artist's rendition of planets around a pulsar.

Finally, if diamond mountains, sodium clouds and eyeball earths still aren’t good enough for you, then take a trip to the first exoplanets ever discovered, orbiting the pulsar PSR 1257+12. These planets are either the charred cinders left over after their sun went supernova, or they formed from the shrapnel generated by that explosion. They are bathed in deadly radiation from their star, and also are in the interesting position of being much larger than the star they orbit (a neutron star is so dense that it can pack the mass of the sun into a sphere the size of a small city). If these planets did indeed form from the gas produced by the supernova, they are almost surely full of exotic radioactive elements generated in the dying gasps of the star. So not only are they blasted by radiation from the pulsar, but they probably produce plenty of radiation themselves. Probably not a nice place to live, but also a fantastic source of resources for anyone who can survive the harsh environment long enough to mine them.

As you can see, the universe is full of fascinating places that are just begging to be the setting for some speculative fiction. I hope these places have sparked your imagination as much as they do mine. It’s fun to imagine other planets, but if there’s anything I’ve learned from studying them, it’s that our imagination pales compared to what is really out there waiting for us.

Author’s Note: This is the first SiMF post picked up for reprinting by io9 — I know it will be the first of many!

Extraterrestrial life is a staple of SF and the focus of astrobiology and SETI.  Yet whereas SF has populated countless worlds with varying success, from Tiptree’s haunting Flenni (Your Haploid Heart) to Lucas’ annoying Ewoks, real ETs remain stubbornly elusive: nobody has received a transmission demanding more Chuck Berry, and the data from the planetary probes are maddeningly inconclusive.  Equally controversial are the shadowy forms on Martian asteroid ALH84001, although the pendulum has swung toward cautious favoring of the biological possibility after scientists discovered nanobacteria on earth and water on Mars.

In part, we’re hobbled by the limits of our technology, including the problems of sample contamination and method-specific artifacts.  But we’re also severely limited by having a single life sample.  Despite its dizzying variations in form and function, extant terrestrial life arose from one source.  We know this because our genetic blueprint and its associated molecular machinery are identical across the three domains (archaea, eubacteria, eukarya).  So to be able to determine if something is alive, we need to decide what is universal and what is parochial.  We stumble through redefinitions each time our paradigms shift or our techniques achieve higher resolution.  Worse yet, our practices lag considerably behind our theories.

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