This is an article about waterworlds, and the search for them. It now appears likely that such planets do exist somewhere in the universe, and if we go far enough, we will undoubtedly find some of them. Scientists have recently calculated that such a body is not only likely, but probable in some planetary systems. Once again, we see an old fantasy which may turn out to be true.
For old folks who grew up reading science fiction, this is a wonderful time to be alive. So many of our old dreams are coming true, and others are at least looking more likely than they once did. When reading about the advances of space science in recent years, there is sometimes an odd sense of pride, knowing that we dreamed the right dreams, way back then. Every great advancement of the human race is preceded by mighty dreams, and ours were mighty, indeed.
One of the perennial dreams of old-time science fiction writers was the waterworld, a world completely or mostly covered with water. This type of world was the setting for countless sci-fi stories. Some writers, looking at cloudy Venus, mistakenly thought that this was a waterworld, while others put their hypothetical planet in another system. The waterworld setting allowed the author to pursue a fascinating idea: what if intelligent lifeforms evolved from aquatic organisms rather than from land animals? Many of these old stories were populated by fish people and such.
Well, the fish people may be out there, waiting for us. In 2003, the European Space Agency held a conference called, “Towards Other Earths,” which was attended by more than 200 experts in the budding science of extrasolar planet detection. At this conference, Alain Leger of France’s Institut d’Astrophysique Spatiale presented a report describing a new class of planet that may be awaiting detection. That’s right: it was our old friend, the waterworld.
According to Leger and his research team, such a planet would have roughly six times the mass of Earth, in a sphere twice as wide as our planet. It would have an atmosphere and orbit its primary star at about one AU- the same distance as Earth from the sun. The planet’s entire surface would be covered with liquid water to a depth of about 100 km., 25 times as deep as any of Earth’s oceans.
Recent discoveries right here in the Solar System have shown us that such a body definitely can form. We now know that we have at least two waterworlds in our neighborhood: Uranus and Neptune. Of course, they’re both so far from the sun that the water is frozen, making them iceworlds. But we also now know that planets can migrate closer to their primary stars over billions of years, so a body that formed in the outer reaches of a system can end up much closer to its primary.
We know this, because we have found several examples. Over the last few years, planetary scientists have detected a number of “hot Jupiters” orbiting other stars. They are often even bigger than Jupiter, and orbit their suns more closely than Mercury does. Now, the current science of planetary formation holds that such bodies do not form so close to their suns. Big planets like that form far out in a system, where water can’t exist in liquid form. This is where they start their long migration inward, caused by gravitational interaction with the accretion disc of dust and gas that surrounds their sun.
At some point in the planet’s inward spiral, the ice melts and our iceworld becomes a waterworld. To make the dream a little more pleasant, let’s say that our hypothetical world goes inward just far enough to have a nice, balmy climate, sort of like Hawaii without the islands. Since this migration is happening very gradually over billions of years, there might be a long period where the planet has a climate suitable for the evolution of life-as-we-know-it. In fact, the time might be long enough for life to develop to a considerable degree of complexity. We’re talking fish people!
There is an interesting variation on the waterworld which may exist closer to home. There is mounting evidence that some of the moons of Jupiter and Saturn, including Enceladus, Callisto and Europa, have internal oceans covered with thick layers of ice. This was a surprise, as these bodies are so far from the sun that any water should be frozen- but nature is full of surprises, isn’t it? While future probes will give us confirmation and more details, it now seems that these worlds offer much more opportunity for life than we once thought. Who knows, the fish people may be closer than we think.
Granted, that’s a longshot, but eventually we may encounter many of these planets, and at least some of them may have life. However, this is not a certainty, since these worlds will probably lack a feature that figured prominently in the origin of life on Earth: hydrothermal vents.
Hydrothermal vents, sometimes called “black smokers,” are openings on the ocean floor that are constantly pouring out vast amounts of hot gas and minerals from deep beneath the Earth’s surface. Here on Earth, such formations have proven to be zones of intense biological activity, with a profusion of lifeforms fed by the energy and minerals of the vent. One theory of the origin of life on this planet is that it started at these vents and spread outward from there. But according to the report presented by Alain Leger and his colleagues, hydrothermal vents would not exist on their hypothetical waterworld.
Remember what we’ve got here: a planet that formed originally as an iceworld, then migrated inward and melted. But when it was at a distance from its star that would allow Earthlike temperatures near its surface, all of the ice would not have melted yet. While a layer of liquid water would cover the surface to a depth of about 100 km., there would still be a thick layer of ice below that, and at the center of that would be the planet’s core. That core would be molten- but all that ice on top of it would effectively cap any volcanic vents, sealing in their heat. Of course, if the planet continued its journey inward toward its star, it would eventually reach a point where all of the ice would melt and the volcanic material would come gushing out, but by that time, the surface would be too hot for the kind of life we’re familiar with. So our balmy world with its Hawaii-like climate probably would not have hydrothermal vents; they would still be buried under many kilometers of ice.
Supposing that these vents were the source of life on the primordial Earth, we are left with the question, would life evolve on a planet that doesn’t have them? We don’t know the answer to this, but scientists are hoping that when they find such a planet, life will have taken the more obvious route: evolving on or near the water’s surface and using the planet’s sun for its energy source.
If humans decided to colonize a waterworld, they would have to live in floating communities. The very idea of living on the frozen ocean floor would be preposterous- imagine the pressure of 100 km. of water! We can envision colonies like enormous buoys, tethered by cables to the distant ocean floor. Or perhaps nature will provide convenient platforms in the form of floating plants. The “lily pad” shape has been quite successful on Earth; maybe our planet will have something like that, only bigger. Our colonists could built their settlement on top, and as long as they didn’t cover up too much of the plant’s sunlight-gathering surface, they would be fine.
Living on a world without dry land would, of course, require some new, outside-the-box technology. Obtaining metals on such a planet would be extremely difficult, since a thick layer of ice would cover the rocky core. Mining operations would have to drill through it to get to any metals underneath- a stupendous challenge. Rather than going through all that, our colonists might be able to find a convenient, metal-rich asteroid that they could move into orbit around the planet and mine.
All this is assuming that our colonists come fully prepared. As we unfortunately know, space missions can sometimes go catastrophically wrong. Equipment fails, and crashes happen occasionally. If we imagine a scenario in which colonists crash-landed on a waterworld with only minimal equipment, the challenges would be formidable. Even if nature had provided them with those giant lily pads, these people would have a rough time. Since one of the very few hard substances in their world would be human bone, it is probable that the bones of the dead would be recycled to make tools. We can picture a case in which Granddaddy’s leg bone gets made into a harpoon, then gets passed down the generations as a family heirloom.
(While it is not the purpose of this article to offer book reviews, it should be noted that the novel The Blue World, by noted science fiction writer Jack Vance, is an excellent treatment of some of the ideas expressed here, especially those in the last paragraph.)
We will find waterworlds, sooner or later. Sooner is a distinct possibility; we are reaching the point where our space telescopes could find such a body orbiting another star. The COROT satellite, a collaboration between the ESA and France’s CNES, is sensitive enough to spot a body that small, and determining how much water is on its surface. (See our article on COROT from a few weeks ago.) The discovery of our first waterworlds could be right around the corner.
And what about those fish people? Well, they may sound pretty far-fetched now, but when you consider that our species evolved from a tiny, shrewlike ancestor with a brain smaller than a marble, the idea of fish evolving into intelligent, technological lifeforms sounds quite believable.
Maybe we’ll meet them someday!
Sources:
ESA Space Science: “Searching for the Real Waterworld” at website of the European Space Agency: http://www.esa.int/esaSC/SEMR96XO4HD_index_0.html
ESA Space Science: “How Do ‘Waterworlds’ Form?” at website of the European Space Agency: http://www.esa.int/esaMI/COROT/SEMYM6XO4HD_0.html
NASA News & Features: “Water World? New Discovery Heats Up Search for Life” at the NASA website: http://www.nasa.gov/vision/universe/newworlds/EnceladusWorld.html