Glass From Nuclear Test Site Shows the Moon Was Born Dry (newscientist.com)

An anonymous reader quotes a report from New Scientist: We can't recreate the giant impact that led to the moon's formation in a lab, but humans have made some other big explosions. By examining residue from the first detonation of a nuclear weapon, researchers have cracked a window into the moon's past. On 16 July 1945, the U.S. army detonated a nuclear weapon for the first time in an operation codenamed Trinity (see photo, above). As the bomb exploded with an energy equivalent to 20 kilotons of TNT, the sand underneath it melted, producing a thin sheet of mostly green glass dubbed trinitite. The explosion brought the area around the bomb to temperatures over 8000 C and pressures nearing 80,000 atmospheres. These extreme conditions are similar to those created as the moon formed in a colossal collision between Earth and another rock, probably about the size of Mars. Fortunately for planetary science, scientists meticulously measured and recorded the details of the Trinity detonation, so there is plenty of information to work with. Day and his colleagues took advantage of that past precision to investigate why the moon has surprisingly little water and other volatiles with a relatively low boiling point -- much less than Earth. To do so, they studied the distribution of one volatile element, zinc, in trinitite collected at different distances out from the explosion's center. They found that the closer to the explosion the trinitite formed, the less zinc it had, especially when it came to zinc's lighter isotopes. That's because these evaporated in the intense heat of the explosion, while the heavier isotopes didn't and so remained in the trinitite. The ratios of different forms of zinc left behind in trinitite showed remarkable parallels to what was observed in the moon rocks retrieved in the Apollo missions. This means that zinc and other volatile elements, most notably water, probably evaporated off the moon while it was being formed in a violent collision or soon afterward, while its surface was still incredibly hot. The study has been published in Science Advances.

Comments

Presumably, the current Earth was also born dry.

[mmell]

It simply makes sense to assume that what we now call the Earth was subjected to intense heating by the impact which was violent enough to form the moon, tilt the planet's axis and accelerate planetary rotation so radically that despite billions of years of slowing it's still slightly over 365 times as fast as it was before the impact. It was one helluva bang. It makes sense to assume that nearly all (if not all) of the water now present on the Earth originated elsewhere.

I've often heard that colonists to the Moon or Mars could generate much of the energy and oxygen they need if they can find water present. How much water is still present in the interplanetary environment, and is it enough to consider using it to augment the fuel/oxygen supply on an interplanetary rocket?

re: Glass From Nuclear Test Site Shows the Moon Wa

[rickyslashdot]

Good Grief. Talk about a bit of over-simplification - - -
article quote - probably evaporated off the moon while it was being formed in a violent collision or soon afterward, while its surface was still incredibly hot.

There WASN'T any MOON surface to evaporate from - it was the multi-quadrillion PIECES that got thermally blasted, and lost all of their volatiles.

Because the major mass-locus was earth, the free-floating material preferentially 'gravitated' here, leaving the particulate residue to accumulate into our moon, with the majority of it's material probably being from the crustal region of the earth and the colliding planetoid (Theia).

With the earth being more massive, and presumably less heated by the collision, the lighter materials would eventually either be 'lost in space' or captured by earth, while the nascent moon cloud, still in it's infancy and HOT, and in FRAGMENTS, continued to out-gas. Even with thermal equivalence of the two bodies, the higher gravitational tug of earth would have preferentially attracted - and kept - the lighter volatiles blown off by the collision. (Yep, I'm agreeing with the author, except on the point of "the moon's surface").

OK, so I'm knit-picking, but please keep your presentation straight, as there was NOT any definable 'surface' of the moon at that period, just a LOT of really hot pieces that thermally expelled all low-temp volatiles as they circled earth and eventually coalesced into our moon.

Still, overall, a very good piece, and worthy of inclusion under the 'real science' category of slashdot's potpourri - unfortunately a small and decreasing category of material on this site.

cheers . . .

Elements

[Muros]

This means that zinc and other volatile elements, most notably water, probably evaporated off the moon while it was being formed in a violent collision or soon afterward, while its surface was still incredibly hot.

Ok, we all know water is an element, but isn't zinc a compound of earth and air?