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Old 12-September-2004, 09:59 AM
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eburacum45 eburacum45 is offline
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Absolutely.

Mars probably had water, but lost it mostly after it lost its magnetic field; the increase in high energy radiation and solar wind slowly destroyed the atmosphere after that.
Venus had water too, and developed a moist greehouse condition before it dried out and this changed to the dry runaway greehouse we see today.

In both cases the main mechanism for loss was probably photolysis, where the water is broken down by ultraviolet light into hydrogen and oxygen. In low mass planets the hydrogen escapes.

So the mass of the planet has a great influence on how much water is on the surface. A high mass Earth would probably be covered in water with no land at all.

Another influence is the impact history; Earth probably lost a lot of water during the impact that formed the Moon, and so we have a smaller ocean cover than would be the case if the Moon had never formed.
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