Ah, astrotropes. It’s been a while. So I’ve decided to delve back into the world of science fiction to see what truth may lie hidden between the laser blasts and epic space battles. The topic I’m examining this time? Ocean planets.
The basic idea is simple. A planet covered entirely, or almost entirely in ocean (essentially the diametric opposite of the desert planet trope). In fiction, worlds like these may often contain some kind of gargantuan sea creatures (such as on the planet Atlantis in The Reality Dysfunction). They may have a few small islands, or they may be completely watery like the planet Kamino from Star Wars episode II.
Some examples, such as the planet Droplet in the Star Trek: Titan books are exceptionally well thought out. Droplet uses some actual science to try and explain how life could thrive on such a world, using the idea of plankton transporting nutrients up from the planet’s deep ocean, providing enough nutrition to support a whole ecosystem. Another interesting example is the planet Yamm from the beautifully detailed Mass Effect universe. In the game, Yamm has a hot climate which fuels powerful global hurricanes, and its predominant form of life is a type of algae which is harvested for fuel.
Interestingly enough though, as science fiction tropes go, the concept of the ocean world is actually somewhat underused. This may have something to do with the fact that most writers are terrestrial creatures. The upshot is that fiction writers, to my knowledge at least, have barely scratched the surface of the ocean planet trope. While the idea is doubtless featured in many books, it hasn’t seen much time on TV or cinema screens. And no, I’m not including that awful Kevin Costner film which, frankly, is probably best forgotten. All the same, the ocean planet is a concept which almost any sci fi fan will be familiar with. Something about the idea, I don’t quite know what, is evidently quite endearing to us all.
We may be happy to know then, that just like the desert planets trope, there’s quite a good chance of actual ocean planets existing in our galaxy. When you consider it, any planet is a sphere of solid material, wrapped in a thin layer of volatile chemicals. Water is the third most abundant molecule in the Universe, so the probability of a planet forming with copious amounts of water in its atmosphere is really very high. In fact, our solar system contains one very good example of such a world – Jupiter’s moon Europa. It may be deep frozen, but it contains more water than all of Earth’s oceans combined.
In fact, this seems to be another trope where the fiction writers are lagging behind a little. Astronomers have already identified several planets which they believe to be candidate ocean worlds. For example, some theories have long held that super-earths – planets with a mass greater than that of Earth, but not high enough to become gas giants – may be able to retain large quantities of water. This is a perfectly logical assertion, given that higher mass enables a planet to hold on to a lot more volatiles (like water). More mass means more light molecules, which is why the Moon doesn’t have oceans. It isn’t massive enough to retain surface water.
Interestingly, if these worlds do contain huge amounts of water, then the pressures at the bottoms of their oceans will be immense. Strange things happen to regular matter at different pressures and temperatures. At high pressures, water will remain liquid even if it’s heated substantially higher than what we consider to be “boiling point”. Compress water enough and you can end up with unusual solid forms. These exotic forms of “ice” can only exist under such high pressures that they tend to remain solid no matter what. Ice-XI, for instance, will happily stay solid at several hundred degrees. Oceanic super-earths then, may have any number of these high pressure ices forming part of their crusts.
Of course, not everyone agrees on all of this. It is certainly possible, given those exotic high pressure ices, that water may become subducted and trapped in the planet’s mantle. If the water ends up mostly in the planet’s interior, then these ocean worlds may not be quite so oceanny after all. However, if it does turn out that super-earths tend to be ocean worlds, there’s a logical conclusion to draw – super-earths are fairly plentiful in the galaxy, so if a certain fraction of them are ocean planets, there may be quite a number of watery worlds out there waiting to be found.
A handful of planets are currently suspected to be ocean worlds, including GJ 1214b, Kepler-22b, and two planets in the Kepler-62 system – Kepler-62e and Kepler-62f. Unfortunately, until our telescopes improve vastly or we discover some means to actually go there, it’s going to be impossible to tell what they’re really like.
Whatever the reality of the situation, I’d wager that there are planets out there in the galaxy with immense oceans of liquid water. Though somehow, I have my doubts they’ll be even remotely like that Kevin Costner movie…
A trope is a recurring theme in any narrative which conveys information to the audience. These are snippets of information which have somehow ended up in our collective subconscious as ways in which storytellers have gotten their points across. Overused tropes end up as clichés.
Banner – “Yamm”, Mass Effect screenshot
Upper – Screenshot from Google Earth. Our own planet is already rather watery.
Lower – Clouds over the Atlantic Ocean, Tiago Fioreze