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Ice Confirmed at the Moon's Poles:
In the darkest and coldest parts of its polar regions, a team of scientists has directly observed definitive evidence of water ice on the Moon's surface. These ice deposits are patchily distributed and could possibly be ancient. At the southern pole, most of the ice is concentrated at lunar craters, while the northern pole's ice is more widely, but sparsely spread.
A team of scientists, led by Shuai Li of the University of Hawaii and Brown University and including Richard Elphic from NASA's Ames Research Center in California's Silicon Valley, used data from NASA's Moon Mineralogy Mapper (M3) instrument to identify three specific signatures that definitively prove there is water ice at the surface of the Moon.
M3, aboard the Chandrayaan-1 spacecraft, launched in 2008 by the Indian Space Research Organization, was uniquely equipped to confirm the presence of solid ice on the Moon. It collected data that not only picked up the reflective properties we'd expect from ice, but was able to directly measure the distinctive way its molecules absorb infrared light, so it can differentiate between liquid water or vapor and solid ice.
Most of the newfound water ice lies in the shadows of craters near the poles, where the warmest temperatures never reach above minus 250 degrees Fahrenheit. Because of the very small tilt of the Moon's rotation axis, sunlight never reaches these regions.
Also at The Guardian and CNET.
Direct evidence of surface exposed water ice in the lunar polar regions (open, DOI: 10.1073/pnas.1802345115) (DX)
(Score: 3, Informative) by takyon on Tuesday August 21 2018, @02:05PM (3 children)
Moon May Have Been Habitable 3.5 Billion Years Ago [soylentnews.org]
The Moon [wikipedia.org] was closer to Earth billions of years ago, and it was rotating faster before it became tidally locked.
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(Score: 3, Interesting) by bzipitidoo on Tuesday August 21 2018, @04:00PM (2 children)
Yes. The current thinking on how the Moon came to be is that early in the solar system's history, when the planets were forming and collisions were frequent, another planet collided and merged with Earth, knocking enough matter off to form the Moon, and giving the Earth a terrific rate of spin. In that scenario, the Moon forms close to Earth. Tides were 1000 feet high, and Earth's day was only 6 hours long. Over the billions of years since, the Earth's rotational energy has been slowly transferred to the Moon's orbit around Earth, causing the Moon to move further form Earth, and slowing the Earth's spin.
If no external interruptions occur, this energy transfer will continue until Earth is tidally locked to the Moon, at which point there will be no more tides, a day will be a month long, but a month will be rather longer than it is currently. I have read it will take about 15 billion years for the Earth and Moon to reach this equilibrium. However, the Sun is expected to exhaust its fuel well before then, in about 5 billion years, and swell into a red giant that might reach the Earth's orbit, in which case both Earth and Moon could fall into the Sun. Also possible that in the process of expanding into a red giant, the Sun will push the planets into higher orbits, and so Earth might not fall into the Sun after all.
The Moon does not have anywhere close to enough gravity to hold onto lighter elements against the constant erosive force of the solar wind. Gaseous matter released by any chemical reaction or heating will be very quickly lost. Of the terrestrial planets, only Earth has the combination of enough gravity (barely) and distance from the Sun to hang onto the lightest element, hydrogen. Earth can't hold much hydrogen, not when it significantly increases the planet's diameter, thus positioning the hydrogen high enough that the solar wind can strip it away.
So yeah, the water on the Moon can only be a small portion of what must have cycled through billions of years ago. Makes perfect sense that remnant surface water would be at the poles, the only places that never get any sunlight. There's no external source in the inner solar system that would add more than trace amounts of water, not for billions of years has there been lots of watery comets zipping about. Lot of interesting questions, like, how much water did there have to be to leave the remnants we see today? How did it get there, as rain in a gaseous atmosphere, or were the poles low elevations that ended up as ocean bottoms, or something else?
(Score: 2) by takyon on Tuesday August 21 2018, @04:26PM
Only a tiny fraction of Earth's mass is water, due to its starting proximity to the Sun. Whereas other objects in the solar system (most past the snow line [nature.com]) can be as much as 50%+ water. Looks like both the Earth and Moon got their water delivered by comets. The Moon may have had a comparatively dense atmosphere and surface water for a while. Which implies that rain is possible.
There could be sources of water trapped underground, and ice in permanently shadowed parts of craters that aren't near the poles.
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(Score: 2) by RS3 on Tuesday August 21 2018, @05:08PM
Yes, but remember Earth's gravity is not enough to hold an atmosphere. The Van Allen belts https://www.space.com/33948-van-allen-radiation-belts.html [space.com] deflect much of the solar wind, protecting our thin shell of an atmosphere. It's theorized that Mars might once have had a good atmosphere, but due to cooling of the planet's core, the belts it may have had would have dissipated and Mars lost most of its atmosphere.