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.
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”:
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 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.
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.
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!
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!
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.