How big would the ice ball have to be to deliver all the water at once?

One popular theory to explain how Earth got its water is that it was delivered by asteroid/comet/etc. The form this theory usually takes is that many small impacts occured over a long time, each delivering a relatively small amount of water until the planet reached its current water content.

But what if 'all the water' was delivered in a single massive event, a single comet or asteroid, a single impact.

What would this event have "looked" like?

Best answers will include details such as size/speed/etc. of the impactor, angle of impact, effects on the geography caused by the impact (impact crater size, or effects on tectonic motion, etc), whether or not the same impact could account for the formation of the moon, etc.

(optional) Bonus question: Since many of us in this community build worlds on different scales, how would these types of impacts change with the size of the planet? In other words, how different would an impact that covers a smaller planet, like Mercury for example, in about 70% water, or how would it be different for a super-earth with double or triple Earth's mass, to be covered by about 70% water in a single impact?

posted over 4 years ago

Dalila‭

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