Correct me if I’m wrong, but I thought most of the Earth’s tides are caused by the moon. This is because the sun is so far away relative to the moon, despite it’s massive size. This is what I gatehred from physics class anyway. So, would this water planet also have a water moon? Would it have a moon at all?
I’d imagine that the very center would cool a bit and eventually turn solid due to pressure. The warmer molecules would probably float to the outside of the planet and carry heat away from the core too.
The effect of the sun on earth tides is less than half that of the moon, IIRC. Anyway, the OP doesn’t mention a moon, so if you want to have one in your model, go ahead.
This *pure *water planet would be almost impossible in real life- although many outer solar system bodies have large water ice components, they are never pure ice…
However, if a fairly pure large water-ice planet did form, it would be far out from the central star, and be frozen -
until the central star ran out of hydrogen to fuse, that is.
Older stars swell up and get hotter as they start to fuse the heavier elements-
I can imagine that many red giants will have ice planets that have melted and become similar to the hypothetical one in this thread- the rocky impurities would form a small solid core, perhaps surrounded by Ice VII or one of those other polymorphic forms of high pressure ice.
A thick layer of water- hundreds of kilometers? would overlay that ice, then an atmosphere of water gas or vapour, some of which could be dissociated by radiation from the swollen sun into hydrogen and oxygen- this would tend to recombine spontaneously.
However the hydrogen that escapes by evaporation into space will leave behind a mainly oxygen atmosphere (together with any impurities that were left from the original iceball.)
If there was any life in the system before the red giant phase it might thrive on such a planet (if it can get there in time).
Look into the sky- a reasonable proportion of the brighter stars that you can see have already left the Main Sequence and are turning into giants- any ice planets around those stars may well have melted and produced a planet similar to the one we are discussing here.
Anyone want to go and take a look?
I don’t think that is correct; the sun and the moon both affect the tides; the moon because it is closer and the sun because it is more massive; IIRC, the differing periods of rotation/orbit is what causes the high and low tide levels to fluctuate - one sine wave modulating/interfering with another, or something like that.
The gravitational force of the sun is same order of magnitude as the gravitational force of the moon. The mass ration and distance ratios balance out. Kinda neat,
Earth
Radius th = 6400 km
Mass = 6 * 10^24 kg
Density = 5.5 g/cm*3
Water planet
Density?
Well, the density of water at STP is 1 g/cm3 and the density of ice VII is 1.66 g/cm3 (from Nim’s link). For a rough estimate, let’s say the water planet density is 1.33 g/cm*3
Mass = 6 * 10^24 kg (given)
so, Radius = 10,200 km
What would the force of gravity be at the surface? Gravity is proportional to square of the distance between center mass, so I get a value of .39g.
Sock_Munkey, what you’re saying is that if the planet becomes tidally locked, then it’ll be tidally locked. If the planet is initially non-rotating, then it’ll be difficult to get it rotating. But if it’s initially rotating, then it’ll be difficult to stop it, too. And the Earth’s oceans are able to move freely enough that they can already form a full-sized tidal bulge, as big as Waterworld would have. Which isn’t particularly big.
Quoth RyanD004:
Correct. The direct force of gravity from the Sun is much greater than that from the Moon, but tidal effects are more strongly dependant on distance than are direct gravitational effects. So because the Moon is closer, it has a larger tidal effect on the Earth. But the Sun isn’t too far behind, and solar tides by themselves would be quite noticeable even without a Moon. To simplify matters, I was assuming that Waterworld doesn’t have a moon, but you can give it one if you want.
And a nitpick to eburacum45’s post: When stars get old and swell up, they get cooler, not hotter. But due to the larger size, they still increase in total brightness. I think, though, that eburacum45 already knew that, and just had a typo.
Yeah- sure- as long as you realise that the core of such a world would probably crystallise under pressure.
As I pointed out there are probably millions of (nearly pure) water planets in orbit around post-Main sequence stars in our galaxy alone, so we might as well try to guess what they are like.
The tapioca/hair moons are likely to come later, when nanotechnology and food production go sadly wrong.
After the monkey hair has soaked in the tapioca pudding and absorbed some of it will it then be more dense than the pudding itself and sink to the core or will it still float and form a monkey hair shell around the planet?
Too much hair and spontaneous combustion has been known to occur.
er
One thing I should point out is that the water would not permit light into the interior of the water planet- apart from the photic zone, there would be hundreds of kilometres of pitchblack water going down into the depths.
Yes, there would be strange currents on such a world- perhaps an equatorial El Nino streaming around the world unhindered, multiple convection cells and seasonal mixing- lots of interesting things going on.
If the planet gets too hot it might even develop a tail like a comet-
recently such a world has been detected, although it is probably a hot gas giant rather than a water world.