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<blockquote data-quote="Warehouse23" data-source="post: 2336813" data-attributes="member: 27941">Harmon--to answer your question: there is some compelling evidence that Mars has lost water (in addition to other light gases) over time. This process is part of a phenomenon called &quot;sputtering, &quot; or &quot;Jeans Escape.&quot; As gas molecules, like water vapor, bounce around an atmosphere, they may reach an altitude where there are so few neighboring gas molecules that at any given moment they may bounce outwards, away from the planet, and not encounter any additional gas molecules to bounce them back planetwards (think of this like billiard balls on a pool table--if you take the bumpers off the sides of the table, the only thing which would keep a ball from rolling off the table, and onto the floor, would be a collision with another ball). Water cannot &quot;evaporate&quot; from a planet--evaporation is just a state change between liquid and gas phase. Water, hydrogen, helium, and other gases can escape from planetary atmospheres, though. The hotter you get the particles (by solar heating, a greenhouse effect, what have you) the larger the gas molecules you can eject.</blockquote>

[QUOTE="Warehouse23, post: 2336813, member: 27941"] [b]Harmon[/b]--to answer your question: there is some compelling evidence that Mars has lost water (in addition to other light gases) over time. This process is part of a phenomenon called "sputtering, " or "Jeans Escape." As gas molecules, like water vapor, bounce around an atmosphere, they may reach an altitude where there are so few neighboring gas molecules that at any given moment they may bounce outwards, away from the planet, and not encounter any additional gas molecules to bounce them back planetwards (think of this like billiard balls on a pool table--if you take the bumpers off the sides of the table, the only thing which would keep a ball from rolling off the table, and onto the floor, would be a collision with another ball). Water cannot "evaporate" from a planet--evaporation is just a state change between liquid and gas phase. Water, hydrogen, helium, and other gases can escape from planetary atmospheres, though. The hotter you get the particles (by solar heating, a greenhouse effect, what have you) the larger the gas molecules you can eject. [/QUOTE]

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