[li]Given: an icy comet or asteroid. Water content high.[/li][li]Then: moved to planetary orbit around dry earth sized world.[/li][li]Would sunlight melt the ice? [/li][li]To vapor? [/li][li]Would the water enter the atmosphere?[/li][li]Would there be orbit effects of the asteroid due to shrinkage?[/li][li]Is this a good way to deliver water to a world being terraformed?[/li][li]Other effects?[/li][/ul]
There is no reason to not send the ice chunks to the surface. They would vaporize on the way down.
If you read the short story “The Martian Way” by Isaac Asimov, some of your questions will be answered.
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[ul][li]Would sunlight melt the ice? [/ul][/li][/QUOTE]
Covering the thing with reflective material is an old proposed solution for that.
Is melting in orbit desirable?
Will the water vapor reach the surface ?
If the iceball is placed in orbit, it melting or sublimating to gas will just result in orbiting liquid / gas. There’s no reason for any particular molecule to decide to drop down into the atmosphere. So an orbiting iceball which *does *melt/sublimate doesn’t end up in the atmosphere (much, aand certainly not any time soon on human timescales). And one which does *not *melt/sublimate just sits there in orbit. Again not doing any good to the planet below.
If you’re trying to deliver water to the surface or the atmosphere, don’t put the iceball in orbit; crash it into the atmosphere.
It’s also a lot more energy efficient to crash it, versus slowing it to just the right speed to remain in orbit after the transfer from wherever it came from.
If you want to terraform the planet you want the asteroids to smash into the surface where most of the water will stay. Read the “Mars Trilogy” for a good coverage of this.
In orbit it would just vaporize; creating a cloud which (not an expert here) would probably be driven away by the solar wind pressure.
Also - odds are it’s a dirty iceball, so if you ever saw a pile of snow plowed off a road: it will get a coating of dirt as the surface water disappears and the dust particles stay behind. For a while that will be heating layer as the darker dust absorbs sunlight, but eventually it may get thick enough to insulate. If the asteriod rotates - not baking one side to the sun constantly - the dust will shed the ehat it absorbs and you will have an orbital source of water that very slowly sublimates.
The ideal method - use some form of heat to create jets to maneuver the ice out of the asteriod or (more likely) kuiper belt. Fusion? Fission? Fusion is best, if by then you have the tech to exploit some of the hydrogen in the water. Thus, you spew some of the asteriod out the back as steam at high speed to make it drop out of orbit toward your target world.
Don’t aim for orbit. First, slowing down to park will be a waste of energy; maybe you could graze the atmosphere first pass to slow down provided you don’t hit anything by mistake. That would also conveniently leave a large amount of water vapor in the atmosphere. (Outlook - torrential rain for the next week…). Also, don’t accidentaly burn up your booster engine units. On the way back, you have predrilled the asteriod - blow it into tiny chunks that create a steamstorm in the upper atmosphere on entry.
If you dump several cubic miles of water as steaming humidity into the upper atmosphere, best if you wait until after to inhabit the planet. If it’s desert, the resulting rains will likely cause serious erosion and flooding. Or else, better have all the settlements on mountain tops.
So maybe Plan B would be to have the asteriod in orbit (some tricky maneuvering there…) and in steady state with it’s dust coating. You slowly gut the interior to drop large ice chunks into the atmosphere until the thing’s gone - maybe supertanker sized instead of one big manhattan-sized chunk.