Science In My Fiction

In less than a month, NASA’s Mars Science Laboratory (MSL) will land on Mars. But to just nonchalantly say “it will land on Mars” overlooks just how hard it is to land on another planet, especially one with an atmosphere. In science fiction, it’s commonplace to see ships land on planets like it’s no big deal, so I thought it would be worth taking a look at what NASA has to do to land MSL safely on Mars next month.

MSL launched on the day after Thanksgiving in November of last year and it has been drifting through space on a collision course with Mars since then. The spacecraft will hit the top of the martian atmosphere at around 8000 miles per hour, and it has to walk a fine line as it slows down and descends to the surface. Slow down too fast and you burn up in the atmosphere. Slow down too slowly… well, then you’re just another crater.

And it’s not just a matter of killing all that excess speed safely. You also want some control over where you end up on the surface. MSL has the most precise landing system ever used for a Mars mission, allowing us to drop the rover into the floor of Gale Crater at the base of an 18,000 ft tall mountain of layered rocks. To do this, MSL actually can steer itself as it is hurtling through the upper atmosphere. Early in the descent, the capsule drops a couple of tungsten bricks, offsetting the center of mass. This shifted center of mass means that the capsule is tilted so that it actually generates lift as it decelerates. Computer controlled jets fire to adjust the trajectory, giving us pinpoint landing capabilities.

Image credit: NASA/JPL

Once the capsule has slowed down to a mere 1000 mph, it is no longer in danger of burning up, so it gets rid of the heat shield and releases a supersonic parachute. This parachute claws at the thin atmosphere and slows the rover down to a few hundred miles per hour.

For previous missions, once the parachute brought the rover close enough to the surface, the rover would disconnect from the parachute and inflate a tetrahedron of giant airbags, allowing it to bounce and roll to a stop. (If you ever had to do an egg-drop project in physics class, it’s like that, but the egg costs hundreds of millions of dollars and if it breaks you will have destroyed a decade’s worth of work by more than a thousand people.)

MSL is too heavy to land on airbags, so the engineers decided to use rockets. The problem is, rockets kick up dust, which can damage the rover’s delicate moving parts and scientific instruments. The solution? Wear the rockets like a jetpack, and then lower to rover on a winch when it gets close enough to the ground.

When the wheels finally touch down, explosive bolts cut the bridle and the jetpack blasts away to crash safely in the distance.

Image Credit: NASA/JPL

All of this takes about 7 minutes. Mars will be about 14 light-minutes away, so the rover’s computer does it all on its own. All of us on the mission will just be watching helplessly. They call it the “seven minutes of terror”:

So, next time you are watching or reading (or writing) science fiction, spare a moment to consider: How are the spacecraft going to solve the problem that NASA’s engineers had to solve for MSL? What are the requirements for the landing? Does it have to be precise, or do they just need to get down safely? How fast is the ship going? How is it going to kill off all of that kinetic energy without killing off the crew? Is it safe for the propulsion system to kick up dust and contaminate the surface, or is a bit more creativity called for? And then, if the ship is like most in science fiction, how is it going to do all of that again and again as it hops from planet to planet? Does it need its heat shield replaced every time? What about parachutes? Fuel?

There’s a reason all Mars missions so far have been one-way trips. It’s hard enough to survive the seven minutes of terror once. Launching from the surface and surviving it again when returning to Earth is not possible. Yet.

Battlestar Galactica burns as it enters the atmosphere.

Neanderthal reconstruction by Kennis & Kennis/Photograph by Joe McNally

I love me some Tolkien. But for everything that The Lord of the Rings has done for the fantasy genre, it has also been so overwhelmingly influential and compelling that it is has spawned entire franchises set in worlds imitating Middle Earth, and has stifled the genre’s creativity. Unless otherwise specified, fantasy is assumed to be set in a medieval European setting and populated by humans, elves, dwarves, orcs, and halflings. Dwarves are always assumed to be great craftsmen and miners who live underground in halls of stone and favor geometric patterns in their art and writing. Elves always inhabit verdant forests, are skilled in magic and craft fine weapons and armor with leaf shapes and magical properties. Orcs are brutish and primitive and wear spiky black armor and wield spiky black weapons. I am hardly the first person to make these observations, and in recent years there has finally been some real progress in emerging from the shadow of Tolkien, but we have a long way to go. I would like to propose just one alternative that not only bucks some of the trends that Tolkien started, but also has some science at its heart.

In most fantasy settings, there are several intelligent species coexisting in the same world, each with a distinctive culture and appearance. In our modern world of course, there are humans of cultures and appearances that vary beyond anything seen in most fantasy, but there are no other similarly advanced intelligent species for us to interact with. This was not always the case. In the course of human evolution, we coexisted with several other species of human, including Neanderthals, Homo floresiensis, and the recently discovered Denisova hominin.

Hominid evolution is a complicated and rapidly changing field, and my summary here will likely make archaeologists and anthropologists cringe, but I hope it will also kindle some ideas for speculative fiction writers looking for something a bit different.

I will start with homo erectus, a species that originated in Africa around 1.8 million years ago and spread across much of Asia into India, China, and Indonesia. Homo erectus was clearly quite successful, and there is evidence that they used stone hand axes and fire, and were probably one of the first hunter-gatherer societies. They stood about as high as modern humans, but their skeletons are more robust and they were more heavily muscled. It is not clear when homo erectus went extinct, but they may have lasted in isolated pockets until relatively recently, and may have interacted or even interbred with early homo sapiens. In fact, Homo floresiensis, which lived in Indonesia as recently as 12,000 years ago, shows some similarities to homo erectus, although homo floresiensis is smaller.

Model of Homo erectus from Museum of Archaeology, Herne, Germany

The most famous hominid that coexisted with humans is the Neanderthal. Neanderthal remains have been discovered throughout Europe and as far east as the Altai mountains. They lived from 600,000 years ago until about 25,000 years ago. Despite the stereotype of Neanderthals as dumb brutes, evidence suggests that they may have been just as intelligent as humans. (In fact their brains were larger than ours!) They made wood, bone, and stone tools, and the discovery of healed fractures in some skeletons suggests that they cared for their sick and wounded. They buried their dead and may have used body paint, and they constructed large shelters out of animal bones. (They also may have practiced cannibalism, but then, so do some modern humans so you can’t hold that against them.) Neanderthals have long been thought of as pure carnivores, surviving by hunting mammoths and other big game, but recent discoveries show that they ate plants too.  Evidence in a cave in Gibraltar, the most recent Neanderthal site, shows that they even foraged from the sea, much like the humans who used the cave thousands of years later.

There is good evidence that Neanderthals used language, and there are even some speculations that their language pre-dated the separation between speaking and music – that it was a hybrid of the two – something that just screams (sings?) to be used in fiction.

So why did the Neanderthals go extinct if they were as smart as we are, significantly stronger, and geographically widespread? There are several theories. One, put forward in the book “The Humans Who Went Extinct: Why Neanderthals Died Out and We Survived” by Clive Finlayson, is that they were simply unlucky. It appears that Neanderthals hunted primarily in wooded areas, ambushing their prey using short spears and relying on their strength to bring the animal down. As the climate changed, the forests receded and gave way to wide steppes. Ambush hunting is less effective out in the grassland: it favors a hominid species specialized for long-distance walking or running, who use projectile weapons. That’s us.

Simulation of the spread of modern humans into neanderthal territory, beginning 1600 generations ago. Neanderthal territory is light gray, homo sapiens territory is dark gray, and the black band indicates areas of coexistence.

Another theory says that Neanderthals competed – perhaps violently – with homo sapiens and that we eventually won. This scenario is appealing from a fictional point of view because it goes against preconceptions and lends itself easily to the tale of a noble species of intelligent (perhaps even musical) Neanderthals being wiped out by a smaller, more devious species of humans: homo sapiens.

Of course, you can go completely in the other direction too. Another theory is that Neanderthals and humans interbred to the point where we stopped being different species. Some Neanderthal remains are sufficiently well-preserved to extract DNA, and the DNA of non-African humans include some portions that match pieces of the Neanderthal genome. Recently, DNA recovered from a 41,000 year old finger bone found in Denisova cave, Russia, shows that it came from a species that is distinct from both Neanderthals and humans, but which shows some degree of interbreeding with both.

My suspicion is that all of these theories are at least partially correct. It is conceivable that even as Neanderthals were dying out as their forests receded, humans could have accelerated their demise. And, knowing human nature, I wouldn’t be surprised if some interbreeding occurred even as our species was killing off the Neanderthals.

All of this evidence for coexistence between humans and other hominids is a ripe setting for fiction much like modern fantasy but with the added benefit of being somewhat realistic. Add in the various exotic mammals that still roamed the world and the changes in climate that drove the migration or extinction of entire ecosystems, and the stories practically write themselves.

The wide geographic range of earlier species like homo erectus, and the persistence of pockets of similar species until quite recently, also spark the imagination. Almost every culture in the world has tales of human-like creatures that live in remote locations on the fringes of civilization. Could these stories be rooted in our distant past when they were not fiction at all? Could the revulsion triggered by the “uncanny valley” be a deep-seated instinct based on a time when there were other humanoids out there, competing with us?

There’s no reason that fantasy has to be confined to a pseudo-medieval Europe populated by the same old fantasy races. Long ago, our planet really was home to multiple species of human, and they fought and loved and explored and invented and sang songs into the night. Let’s hear their stories.

We’ve all seen the utopian cities in science fiction and fantasy where people live in harmony with nature in overgrown tree forts, flitting from tree to tree on vines or suspended walkways. From Tolkien’s Lothlorien to the Home Tree in Avatar to the treeships in Hyperion and the Ewoks and Wookees of Star Wars, it seems that living in a tree-house is all the rage for the more eco-conscious species. But is arboreal living really the greenest way to live?

Tolkien's elves might be able to pull of eco-friendly living in the trees, but mere mortals are better off living in cities if they want to protect the environment.

Read the rest of this entry »

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.

Arthur C. Clarke famously said that “Any sufficiently advanced technology is indistinguishable from magic.” I always keep this quote in my mind when reading science fiction and try to spot where things become indistinguishable from magic. They always do. One of the most popular ways in modern sci-fi to get away with magic is to invoke nanotechnology. It seems that if you just wave your hands and say “nanobots” you can get away with anything!

With that in mind, I thought it would be interesting to take a look at some real-world nanotechnology. What is actually plausible and what is still truly magic?

First let’s get this out of the way: I don’t think we’re going to see swarms of tiny robots doing our bidding (or reducing the world to a seething gray goo) any time soon. The reason? Well, aside from the fact that it’s just really hard to build things so tiny, and even harder to tell them what to do and how to do it, there’s the minor fact that we already live in a world crawling with molecular machines of such stunning precision and elegance that we will never be able to do better. Turns out that instead of a doomsday scenario of gray goo, a planet-enveloping swarm of fully-functioning microscopic self-replicating entities leads to the spectacular and rich biological ecosystems we see all around (and in) us.

I’ve written before about the idea of biotech and nanotech merging to lead to a sort of biological singularity, and biology as nanotech has also been discussed before here at SIMF, so rather than rehashing it again, I’ll just point you to those two posts and move on.

Instead of nanobots, some of the most successful applications of nanotechnology are actually in designing new materials at the molecular level. It turns out that you can get some really startlingly cool materials when you have great control over their molecular structure. Even within the subfield of nanomaterials there is a lot to cover, so I decided to focus on two types of nanomaterial in particular: aerogels and carbon nanomaterials.

Aerogel is an almost perfect insulator. Here a thin slab of aerogel is able to protect a box of matches from a blowtorch! Phot0: NASA/JPL

Aerogel is the least dense solid substance known – the record-holding aerogel has a density of 1.9 milligrams per cubic centimeter. That’s just slightly more than the density of air! The most common aerogels are made of silica particles that are put into suspension in a liquid and allowed to form a gel. Then the liquid is removed, leaving an airy structure of nanometer-sized silica spherules bonded together into branching fractal chains. Even though silica aerogels are the most common, other materials such as carbon, aluminum oxide and various metals have also been used.

Because of their extremely low density, aerogels are almost perfect insulators, so as they become more affordable to produce they are making their way into extreme cold-weather clothes and blankets and thin slabs of transparent aerogel are being used in windows. NASA loves the stuff: it has used aerogel to capture dust grains from a comet in the Stardust mission, and as insulation on the Mars rovers and in space suits. Aerogel also has some very useful chemical properties: since it has an enormous surface area, it can be used to absorb chemicals such as heavy metals very efficiently, making it great for cleaning up pollution. Its surface area also makes it useful as a catalyst for chemical reactions, such as in fuel cells.

Another class of nanomaterials with a seemingly endless list of useful properties are carbon allotropes. Picture chicken wire made of individual carbon atoms bonded together. This mesh of carbon is graphene, a molecule 200 times stronger than steel yet transparent and electrically conductive. It was originally isolated by using scotch tape to remove single layers of carbon atoms from graphite, but in the last few years scientists have finally figured out to produce large sheets of graphene, and the 2010 Nobel prize in physics went to researchers studying this amazing macromolecule. As it gets easier to produce and manipulate, you can expect to see graphene making an appearance in everything from touchscreens and compact electronics to high-strength composite materials and solar panels.

But graphene is just the beginning. Take these sheets of carbon and roll them up and you get carbon nanotubes. These tiny cylinders of carbon have the highest tensile strength of any material known, are harder than diamond, and as of 2010 can be up to 18 cm long. And of course they conduct electricity just like their relative graphene.

An animated view of a carbon nanotube structure. Source

Sci-fi readers are probably most familiar with nanotubes as the key component in building a functioning space elevator: their extreme tensile strength for their weight makes them ideally suited for the ultra-strong cable that would be necessary. But nanotubes have more uses than just building long, strong cables. In fact, they may have been used thousands of years ago, before anyone knew about atoms or molecules, let alone nanomaterials! Anyone who knows a bit about swords has probably heard of the famous “Damascus steel” that caused the Crusaders such grief. Well, it turns out that the alloy Damascus swords are made of – called “wootz” and originating in India – might actually contain nanotubes grown when impurities in the ore catalyzed the growth of carbon from smoke in the forges.

But fancy swords and space elevators aside, there are an almost endless list of modern uses for carbon nanotubes. For instance: bulletproof t-shirts. Mats of nanotubes have been made into incredibly strong and thin sheets. A stack of 100 sheets, about a millimeter thick, can stop a bullet. That doesn’t mean that if you’re wearing nanotube fabric being shot won’t hurt, but it stops the bullet and that’s not bad for such a thin fabric!

Another surprising use for carbon nanotubes is in paper batteries. That’s right, by combining carbon nanotubes and cellulose fibers like those in normal paper, researchers have created a material that stores energy like a battery but looks and feels like black paper. The nanocomposite paper batteries store energy at temperatures ranging from -100 to 300 degrees Fahrenheit – much better than typical batteries – and work if they have been folded, rolled or even cut!

An electron microscope image of carbon nanotubes being extracted for use as synthetic muscles. Credit: Mei Zhang

Carbon nanotubes might even be used as artificial muscles! Nanotube muscles are actually based on carbon nanotube aerogels, and can expand to three times their original size in one direction when a voltage is applied, and then shrink back to their original size when the voltage is released. By combining the lightweight properties of aerogel and the electrical properties and great strength of carbon nanotubes, these synthetic muscles could be ideal for space exploration, where weight and energy are at a premium and temperatures can be far too hot or too cold for other synthetic muscles or more traditional mechanical systems to work. So far, nanotube muscles require too high a voltage to be practical for human prosthetics, but that’s a pretty minor detail for sci-fi.

Of course, it’s impossible to cover all of the awesome new materials that are the result of nanotechnology research, but I hope I’ve made it clear that even if swarms of nanobots are not likely, there are some really amazing developments coming out of nanotechnology research. There’s plenty of material that is ripe for the science fictional picking without resorting to clichéd nanobots. And even though things like paper batteries or artificial muscles or bulletproof t-shirts sound suspiciously like technology that is advanced enough that it is “indistinguishable from magic”, they already exist and even more exciting applications are right around the corner.

Now, let’s get to work on that space elevator.

Artwork from StarCraft, showing a creep-infested platform near the planet Char.

“What the hell is that? Looks like the ground there is alive.” – Jim Raynor

Creep: that purple, fibrous, living mat that extends from zerg “buildings” in the computer game StarCraft. Its ominous presence always tells you you are entering unsafe territory, unless of course you’re playing as zerg, in which case it says “welcome home”! But what exactly is it?

Well, let’s think about it scientifically. It is produced by zerg buildings and spreads across any available surface. According to the Starcraft Wiki (which I will use as an authoritative source for all the minutiae of StarCraft trivia that I don’t know) Creep has a cellular structure: it’s not just mucus. The Wiki also says that creep can absorb sustenance from the underlying terrain, that it can be spread by “spores” or excreted by several units, and it provides nutrients to zerg buildings. It is averse to high temperatures but can grow in space and over water.

So, does any real-world living thing match this description? Surely not, right? Wrong. The closest analog that I know of are slime molds. You’ve probably seen slime mold before without knowing it. They are a type of fungus, often brightly colored and found growing on damp logs in the forest. They are also incredibly weird.

Some types of slime mold are made of multiple cells joined together to form a super-cell with a shared cytoplasm. Ok that’s weird enough, but the other kind of slime mold starts off as a bunch of separate single-celled organisms, which can then coalesce into a multi-celled organism.

In terms of similarities with creep, slime molds are spread via spores but can also grow and multiply when they encounter nutrients. Slime molds can become quite large, and form branching networks of cytoplasm, allowing the leading edge of the slime mold to stream nutrients back to the rest of the “organism”.

A slime mold branching out and looking for food.

When the going gets tough for a slime mold and nutrients run out, it can transform and form structures called sporangia, which distribute spores. In some cases, separate cells will coalesce into a single “creature” in order to do this.

There are some definite similarities between slime molds and creep. They both come from spores but can also grow across nutrient-bearing ground. They both can transport nutrients to locations within them that need them, and are averse to hot, dry conditions.

There are some aspects of slime molds that would have been very interesting if they applied to creep. Most notably, slime molds have been reported to show some rudimentary intelligence. No, they don’t sit there and ponder the meaning of life, but they have been able to choose the most nutritious food and can “solve” mazes to get to food sources. These aren’t true intelligence, they are actually an example of something called ant-colony optimization, often used in computer programming.

The slime mold starts out evenly spread through the maze, but when food sources are placed at two ends, the slime mold retracts from everywhere but the shortest path.

The idea is that you don’t know what the best set of steps to reach a certain goal is, so you test things out randomly. Some sets of steps don’t give you the goal, but others do. The ones that do give good results are reinforced, while the ones that don’t, are not. The analogy is that ants start off randomly searching for food, but when they find food, they emit pheromones encouraging other ants to follow the same path, so eventually you end up with the familiar narrow stream of ants going from the nest to the food and back. The exact same principle applies to slime molds.

That’s nice, but weren’t we talking about creep? Yes! My point is that creep could behave like this too. There’s not necessarily a need for it to be spread evenly across the ground. It would make more sense for it to have thick branches connecting zerg structures (so that large amounts of nutrients could be provided) while narrower branches near the leading edge of the creep could do the work of absorbing nutrients.

Just to play devil’s advocate though, I can see why it might spread across the ground evenly (other than because it makes the game more intuitive to be able to see a clear boundary to the creep). If it is able to suck nutrients out of any surface, then it wouldn’t have to concentrate on certain areas. And by not coalescing into thick “veins”, the creep is more robust: there’s less chance of a building being cut off if there are many smaller veins feeding it.

Finally, all of this brings me to an interesting point: if creep can extract it’s own nutrients, and if it is the way that zerg structures are fed, why do the zerg have to mine for minerals? They should just be able to engulf a mine in creep and let it do the work! That would certainly make for a different zerg strategy, especially if a “creeped” mine could not be used by other players!

Obviously the creep is still pretty science fictional. I mean, it can grow in space! There are actually some real-world spores that can survive in space, but I think the whole “zerg don’t need spacesuits” issue needs to be tackled in a future post. But from now on, when you see creep, think “slime mold” and when you’re out in the woods and you see a slime mold, be glad you don’t have to watch out for zerglings!

This post originally appeared on the Science of Starcraft blog.

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.

Earlier this year I spent a week out at Los Alamos National Laboratory vaporizing things with a high powered laser. Now, as I drown in data that I collected out there, I thought I’d take a moment to talk about lasers. When I tell people that I zap things with lasers, I can almost see the mental images flickering behind their eyes. They tend to look something like this:

Man, I wish. I hate to burst your bubble, but working with lasers, although very cool, is not as showy as most sci-fi depictions. To help understand why, let’s first talk about how lasers work. The word laser is actually an acronym for Light Amplification by Stimulated Emission of Radiation, and that actually sums up how they work quite well. There are lots of different types of lasers these days but they all share a few common characteristics. First, you need the “lasing medium” – that is, the stuff that will give off the light. The first lasers used artificial ruby crystals, but now there are lasers that are based on everything from CO2 gas to organic dyes to various semiconductors. The laser I use for my research is a Nd: YAG which stands for Neodymium-doped Yttrium Aluminum Garnet crystal. Ok, so we have a “lasing medium”, now we need to make it shine. Things give off light when they have electrons in high energy levels jumping back down to lower energies and getting rid of the excess energy as photons. In a laser, the goal is to get something called “population inversion”, meaning that there are more electrons in excited energy levels than there are in the ground state. This is typically done with a flash lamp in a process called “pumping“. By shining very intense light on the lasing medium, the electrons all get excited and the laser is ready to, well, lase.

Diagram of a ruby laser from HowStuffWorks.

Of course, the goal of a laser is to have a nice narrow beam, but if you just have a lump of stuff with excited electrons, the light will be given off in all directions. A fluorescent bulb is a good example of this. A lasing medium acts in much the same way, shining a diffuse light in all directions, unless we do something to it. The secret is to place it between two mirrors, one which reflects all light, and one which reflects only some of the light that hits it. Initially, the atoms in the lasing medium give off light in all directions, but some of those photons will end up traveling along the laser, bouncing back and forth between the two mirrors. Here is where the laser really starts working. It turns out that when you have photons of a certain energy traveling along through a bunch of atoms with excited electrons that have the same energy, you get “stimulated emission“. The first photons cause the electrons to jump down and emit identical photons. And I do mean identical. Yes they have the same energy (and therefore the same frequency/wavelength/color), but the new photons also have the same phase, polarization and direction as the initial ones. They are completely indistinguishable at the quantum level. As you might expect, this stimulated emission leads to a chain reaction. Each photon of laser light can stimulate new photons to join it. Since one end of the laser is partially transparent, the result is a narrow beam of light made up of identical photons: a frickin’ laser beam! Wonderful. Now that we understand how they work, I want to address a few misconceptions about lasers in science fiction and popular culture in general.

1. Laser beams are visible.

With a laser, the idea is to have all of the light going in the same direction, right? That means that if you can see the laser beam from the side, as shown in this picture from Star Trek, and in pretty much every depiction of lasers ever, then something isn’t right! The light is being scattered out of the beam. If you’ve ever used a laser pointer you know that even though it gives off visible (usually red or green) light, you just see a dot where it is pointing. Now, if you shine it at someone who is smoking, or if you use it outside in the fog, or in a dusty room, you can see the beam because the light is reflecting off of particles in the air (smoke or water droplets or dust). So, yes sometimes visible lasers in air are plausible because there could be stuff in the way, but visible lasers in space? No way! There are some other caveats to this also. Not all lasers use visible light! The Nd:YAG that I use for my research and the similar laser used by ChemCam emit infrared light. It is completely invisible, no matter what. This makes it incredibly dangerous to work with lasers like this, especially when first lining up the optics, because you can’t tell if the laser is being reflected around the room! Just because these lasers are not visible doesn’t mean they can’t destroy your retina in a millisecond, so we wear special protective goggles designed for the specific wavelength that the laser emits at all times when the laser is on. Also: you can’t see the laser beam traveling from the source to the target. It’s going at the speed of light. So all those sci-fi depictions of laser blasts whizzing by the hero’s head like tracer bullets: wrong.* *Yes, I know, some sci-fi explains this by invoking pulses of plasma and not actual lasers. That’s a whole different can of worms with its own issues. Suffice it to say that most people *think* those blasters, phasers, etc. are supposed to be lasers, so I’m debunking that misconception.

2. Pew pew pew!

That’s not what they sound like. I know. I’m sorry. Low powered lasers don’t really sound like anything. And can you imagine how annoying it would be if they did? At the grocery store checkout: pew pew pew! Using a CD or DVD player: pew pew pew! Laser pointer: pew pew! Yes, but the “pew pew” sound really comes from things like Star Wars, depicting lasers used as weapons. So what about big lasers, capable of vaporizing things? Nope. With higher powered lasers, at least the kind I work with, the main sound comes from the flash lamp. It’s sort of a ticking noise, one tick per flash, one flash per laser pulse. Now, when we crank up the power or use something called a “q-switch” to make each pulse shorter and more intense, you get another noise that comes from the laser actually vaporizing things. That noise is more of a “crack” or “pop” noise. In fact, I once popped some bubble wrap in the laser lab while my collaborators were aligning the laser and totally freaked them out because they thought it was the laser. Oops… The popping noise is essentially the same thing as thunder: a rapidly expanding ball of plasma causes the air to be compressed in a shockwave. Our laser plasmas are tiny, so they just make a little noise. Lightning bolts (plasma formed by electrical discharge) are rather larger, and so is their noise. Many of my experiments are done zapping rocks inside a vacuum chamber, and it’s always fun to hear the noise fade away as we decrease the air pressure in the chamber.

3. Lasers as weapons.

They’re really not that great. There are a lot of issues with using lasers as weapons. First of all: the optics. For a laser to be useful as a weapon, you would have to focus the light as tightly as possible on the target. De-focus at all, and you might still blind them, but there won’t be much vaporization going on. The precision required for the optics to do this makes a hand-held laser really impractical. The slightest bump or wiggle and all of a sudden your gun is a high-powered flashlight. There’s also the issue of air. Anyone who has looked through a telescope or out over a parking lot on a hot day has seen the shimmering mess that the air can make of an otherwise clear image. Now imagine trying to shine a tightly focused beam of light through that mess and hitting a target. Not an easy task. The military has worked on this to some extent with adaptive optics used for giant plane-mounted anti-missile laser, but it is a significant problem. The air poses another problem: it absorbs light. In fact, a high enough powered laser can cause the air itself to break down into a ragged line of plasma. I’ve seen this in the lab and it is awesome. The problem is that plasma is full of free-flying electrons, so it absorbs light. A laser strong enough to use as a weapon would also be strong enough to turn the air to a plasma, which would then block the laser from hitting its target. One way around the plasma problem is to use a pulsed laser. As long as the pulses are timed so that the plasma has dissipated before the next pulse is fired, the plasma is not as much of a problem. I mentioned lightning earlier and that’s relevant here. There is a way to make use of the “plasma issue”, because plasmas conduct electricity. So in theory it would be possible to use a laser as a long-distance taser! The laser would first create a conduit of plasma out of the air, and then with a high enough voltage, an electric shock could be send down the plasma to the target. This would not be a subtle weapon: at this point the lightning analogy is not really an analogy anymore. It would basically be a lightning gun, and would make a noise to match. I thought I was being really clever when I thought of this, but it turns out I’m not the first: the US military has experimented with them. Another problem with lasers as weapons is the power source. It takes quite a lot of power to make a laser capable of doing damage, and it would probably not be practical for a person to carry such a power source around. In the video game “Fallout 3″, the energy weapons use things called “microfusion cells” for ammunition to get around this issue. But right now, we don’t even have power-positive macro-fusion cells, so bullet-sized fusion powerplants are not available yet.

Finally, there is the issue of collateral damage. The thing with light is that it tends to reflect off of things. This means that anyone using a laser weapon better be wearing the appropriate protective eyewear or else their own target is going to blind them. Aside from the practical issues with blindness, the Geneva conventions also specifically forbid laser weapons that cause blindness (in other words, all of them). In my opinion, I highly doubt that lasers will ever be practical as pistols or rifles. Maybe as large mounted guns on tanks or something. But really, the most likely place for lasers as a viable weapon is space. Without air, the difficulties with plasma creation and turbulence are removed. The issue of power and optics remain, but I could plausibly see a satellite or space station with the stability and power to use a laser as a weapon. It might still be difficult to focus on a distant target, just due to the physical limits on the optics, but the advantage of near-instant travel-time might be of benefit when you’re aiming at a target thousands of km away, traveling at thousands of km per hour.

This post reprinted with permission from Ryan Anderson’s blog.