How much water on Mars?

Couldn’t Mars have perhaps as much water as Earth (proportionally) since both planets were formed from the same grab bag of stuff at the same time?


If Mars once had more water than it does now, where did it go? How could it escape the planets gravity well?

Mars doesn’t have enought gravity to prevent water from escaping (and other gases). Some think Mars was once a warm wet place - possibly better at supporting life then earth. but the atmosphere was lost to space and the planet cooled till what we have today. perhaps mars does have such water reserves underground but probabally somewhat less then earth.

The NASA spacecraft Mars Odyssey is now orbiting Mars. One of its missions is to find out the amount and distribution of water there. Most is assumed to be in the form of subsurface ice.

I have to disagree with you, k2dave. Mars does indeed have enough gravity to prevent water vapor from escaping. Or at the very least, it wouldn’t escape very quickly and it is still abundant in the Martian atmosphere (even the Hubble telescope can see ice-fog clouds on Mars).

ready29003, it’s thought that Mars’s water didn’t “go” anywhere; it didn’t leave the planet, anyway. A lot of it is underground in permafrost, some is under the icecaps (mostly at the North Pole), and some is thought to be in subterranean aquifers. Just how much is there is yet to be determined.

Mars’s current atmosphere is too cold and too arid to allow liquid water to exist on the surface. That’s what scientists mean when they say the water is “gone.”

As for how the water got there, and its abundance relative to Earth: we’re not sure where Earth’s water came from. There is some speculation that much of it might have come to Earth as comets.

Comets are made of water ice, and in the early days of the solar system comets and other objects rained down on the planets with great frequency.

Mars, being much less massive than Earth, wouldn’t have attracted as many comets. Whether it still would have gotten as much, “proportionally,” I couldn’t say.

fiver perhaps mars’s gravity is stronger then I give it credit for but if mars had great oceans like some have speculated then mars had to lose some of it. IF the oceans did exist then I would assume Mars did have a subsurface water table and the 2 were in equlimrium. The water had to go somewhere to ‘dry’ up the oceans.

I remember from the various books I have read on Mars, the volume of water ice as opposed to dry ice in the Martian polar ice caps is the equivalent to the Greenland ice cap. This is enough if melted to cover the entire planet to a depth of 30 or so feet, if I remember correctly.

k2dave, you’re right that it had to go somewhere, but wrong that it had to leave the planet. It’s mostly bound up in the permafrost. Look at this photograph:

That’s a so-called “splosh” crater on Mars. Notice the rounded, muddy pattern of the ejecta?

It’s thought that this terrain is all permafrost. When the object that caused this crater hit, jillions of tons of permafrost was converted into mud by the heat and “sploshed” out to form this pattern. The pattern is consistent with permafrost, but not with dry soil.