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banquo's_bumble_puppy
2011-Apr-18, 11:23 AM
Could an ocean exist in space? If it were in the goldilocks zone? I'm talking about a body of water with no core....just water...

Noclevername
2011-Apr-18, 11:32 AM
A "water giant?" Something like an ocean planet (http://en.wikipedia.org/wiki/Ocean_planet)?

banquo's_bumble_puppy
2011-Apr-18, 11:40 AM
Could an ocean exist in space? If it were in the goldilocks zone? I'm talking about a body of water with no core....just water...

well no core...but according to your link the core could be the exotic ice

Noclevername
2011-Apr-18, 11:45 AM
I think I remember the episode you mean-- an Earthlike planet's ocean was stripped off the planet and put into space for Zeus knows what reason-- but in that episode they had some kind of gravity generators or force fields holding it all together. In reality, a mass of water the volume of Earth's oceans orbiting in the habitable zone most likely wouldn't have nearly enough gravity to keep from evaporating into space within a few years. It would have to be orders of magnitude bigger.

publiusr
2011-Apr-18, 11:01 PM
Surrounded by a transparent sphere one would hope...

Noclevername
2011-Apr-18, 11:41 PM
Surrounded by a transparent sphere one would hope...

Well, the one in the show didn't have one.

Jeff Root
2011-Apr-19, 03:28 AM
http://www.bautforum.com/showthread.php/32649-A-Big-Ball-of-Water
http://www.bautforum.com/showthread.php/44502-100-water-planet.

-- Jeff, in Minneapolis

chornedsnorkack
2011-Apr-20, 07:34 AM
In reality, a mass of water the volume of Earth's oceans orbiting in the habitable zone most likely wouldn't have nearly enough gravity to keep from evaporating into space within a few years. It would have to be orders of magnitude bigger.

No, not a few years.

Volume of Earth oceans means a sphere about 1400 km diametre (a bit bigger than Charon).

It would rapidly freeze by evaporative cooling. And then the evaporation into space would be slowed indeed not by gravity (I get escape speed slightly over 500 m/s) but nevertheless by the cohesion and heat of evaporation of ice. Sunlight in habitable zone can evaporate, by my calculations, about 18 m ice from surface directly exposed to sunlight, about a quarter that from the sphere on average. So an iceball 700 km radius should take about 150 000 years to evaporate in habitable zone.

Jeff Root
2011-Apr-20, 10:39 AM
Sunlight in habitable zone can evaporate, by my calculations,
about 18 m ice from surface directly exposed to sunlight, about
a quarter that from the sphere on average.
Did you leave something essential out of that sentence?
Possibly two somethings? I can't figure out what you mean by
"that from the sphere".

Would the water world be shrouded in solid clouds? Would it be
raining or snowing everywhere almost continually?

-- Jeff, in Minneapolis

chornedsnorkack
2011-Apr-20, 11:08 AM
Did you leave something essential out of that sentence?
Possibly two somethings? I can't figure out what you mean by
"that from the sphere".

The surface of a sphere is 4 times the surface of great circle intersecting it. Therefore, the illumination of a sphere, on average, is one quarter that of a surface normal to sunlight, and so is evaporation of ice.


Would the water world be shrouded in solid clouds? Would it be
raining or snowing everywhere almost continually?


Would there be any sinking of water vapour?

Noclevername
2011-Apr-20, 03:35 PM
Question: How long would it take to freeze? If it's in the habitable zone, would solar tides pull it apart before it had a chance to solidify?

Jeff Root
2011-Apr-20, 04:27 PM
Sunlight in habitable zone can evaporate, by my calculations,
about 18 m ice from surface directly exposed to sunlight, about
a quarter that from the sphere on average.
Did you leave something essential out of that sentence?
Possibly two somethings? I can't figure out what you mean by
"that from the sphere".
The surface of a sphere is 4 times the surface of great circle
intersecting it. Therefore, the illumination of a sphere, on average,
is one quarter that of a surface normal to sunlight, and so is
evaporation of ice.
Okay, that explains the final clause. I would have needed a lot
of guesses to guess that that was what you meant. What about
the "18 m ice" figure? 18 m of ice depth evaporates in total?
No. Per year? That would give a figure of 39,000 years, not
150,000. I'd expect the evaporation rate to be really difficult to
calculate. Is it based on Earth conditions?




Would the water world be shrouded in solid clouds? Would it be
raining or snowing everywhere almost continually?
Would there be any sinking of water vapour?
Huh?? That is totally cryptic!

-- Jeff, in Minneapolis

Jeff Root
2011-Apr-20, 04:32 PM
Solar tides wouldn't pull apart a body of water 1 AU from the Sun.
It would need to be way closer to the Sun.

-- Jeff, in Minneapolis

eburacum45
2011-Apr-20, 07:15 PM
Olaf Stapledon, in StarMaker, imagined artificial worlds made of water, filled with aquatic and amphibian species. The largest possible liquid-water-world would have (according to Grant Hutchison's calculations) a radius larger than 2675 km and smaller than 8461 km, this being dependent on the temperature at the core.

If we want to have aquatic species living at all depths within such a ball, we would need to make sure the temperature was not too high. But remember the biota living in hot water around those deep-sea vents on Earth; life can thrive in quite hot water. So we could have a quite large, quite warm water globule absolutely filled with life; probably as big as Mars.

One reason such an artificial watery habitat would be so hot is the fact that it would need to have a lot of internal illumination, assuming that the inhabitants use light to see or eat photosynthetic crops. If instead the inhabitants are blind and devour food grown without light, then the interior of this world could easily be dark (and cooler). Water absorbs light very efficiently and such a globe would be pitch black except for the top few hundred metres.

chornedsnorkack
2011-Apr-20, 07:57 PM
Okay, that explains the final clause. I would have needed a lot
of guesses to guess that that was what you meant. What about
the "18 m ice" figure? 18 m of ice depth evaporates in total?
No. Per year?
Per year.

That would give a figure of 39,000 years, not
150,000.
Yes, but I was including the average evaporation being a quarter of this.

I'd expect the evaporation rate to be really difficult to
calculate. Is it based on Earth conditions?

Yes. The evaporation rate gets more difficult to guestimate when gravity is significant in hampering the escape of vapour.

Look at it this way: one square m at Earth receives 1,4 kW, or 1400 J per second. Which is about 330 cal. A gram of ice needs about 600 cal heat of evaporation. So about 0,55 g per second per square m.

Which means around 50 kg per day (86 400 seconds, remember back of the envelope order of magnitude estimation with one significant digit or less). From square m, meaning about 5 cm layer per day. 365 days giving the number of 18 m.

The above reasoning omitted reflection of sunlight due to albedo, as well as radiation of infrared. Both will tend to slow down evaporation. So, the 4,5 m per year is very much upper bound.

What I proved above is that a Kuiper belt object sized snowball wandering into habitable zone cannot evaporate "in a few years", nor even a few thousands of years. The order of magnitude is a few hundreds of thousands of years - provided that the escape speed does not exceed a couple of km/s.


Huh?? That is totally cryptic!

If water vapour sinks over any region, it warms adiabatically and clears.

Noclevername
2011-Apr-25, 05:11 PM
No, not a few years.
... So an iceball 700 km radius should take about 150 000 years to evaporate in habitable zone.

Well, that's a few years, isn't it? ;)

baric
2011-Apr-25, 07:01 PM
Well, that's a few years, isn't it? ;)

In planetary terms, it's the blink of an eye :P