What could cause the world to be almost completely submerged in water, naturally or man-made?
I'm trying to build a world that is almost completely water, but I couldn't come up with an explanation for WHY the world was like this. The world has the same gravity and atmosphere of Earth. It also had to have basically the same land structures. What could have happened to this planet to make it this way?
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The idea of an ocean planet isn't too far-fetched. There are several moons in the Solar System - Enceladus and Europa, for instance - that have subsurface oceans. If the ice covering their surfaces melted, they'd be just what you're looking for. Extrapolating that to a larger, planetary-mass body isn't too hard.
Creating an ocean planet isn't too difficult:
- It would likely have formed in the outer reaches of the planetary system (beyond the frost line), where volatiles (think molecules like water and ammonia) are plentiful. These areas are where giant planets form, as well as ice-rich bodies like comets.
- The planet would then have migrated inwards, due to interactions with other planets or the protoplanetary disk. If it came close enough to the star, the icy covering it would have developed might melt, forming an ocean surrounding the planet.
- Rather than a block of rock and ice, you now have a block of rock and (largely) water.
There are some things to consider, though. The atmosphere will likely be water-heavy; you're not guaranteed a nice mixture of nitrogen and carbon dioxide (followed by oxygen, if life arises to produce it - and all you need is a lot of bacteria!). Ammonia might also be present, a relic of the planet's formation farther out form the Sun. None of this precludes aquatic life, of course.
There are several excellent candidates for ocean planets:
It's interesting to note that two of these are in the same system, orbiting Kepler-62. Also, if you peruse this list, you'll note that they do run the gamut of Earth-mass planets. If you look at enough ocean planets, you'll almost surely find one with a surface gravity of roughly $g$, 9.8 meters per second squared. Honestly, if you don't mind some rather dull views, life on an ocean planet would be quite manageable for, say, human colonists, given the right atmosphere and the right tech.
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