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The Moon's watery past

Gilvarry's calculations regarding the behavior of water and atmospheric gases on the Moon were made with great care-they were based upon Sir James Jeans' calculations of the amount of time it takes a planet's atmosphere to escape into space.

Gilvarry demonstrated that our natural satellite could have supported an Earthlike atmosphere and surface water for millions of years - that's short by Earth's atmospheric and hydrospheric timeline, but still long enough to be interesting. When astronomers today say the Moon is too small to have supported either an atmosphere or liquid water, they may need to review the math. According to Gilvarry's data, our Moon, a dwarf planet of sorts, could have retained an appreciable atmosphere long enough for it to act as a "lid" on surface water.

An intriguing footnote: Gilvarry employed Baldwin's curve of crater depth-diameter values alongside U.S. Atomic Energy Commission crater data gleaned from the "Ivy Mike" fusion-device test in the Marshall Islands in 1952. Why? Well, while most of the Moon's highland craters fit Baldwin's depth-diameter curve for impact craters formed on land, the shallow slope lunar maria (the so-called "lunar seas") matched Baldwin's depth-diameter curve of a typical impact crater formed in deep water. According to Gilvarry, the maria profiles looked a lot like the underwater crater that marks ground zero of the "Ivy Mike" shot. (The explosion vaporized the Marshall Islands atoll of Elugelab and left behind a 6,240 feet wide submarine crater.)

Gilvarry might have relished the irony of demonstrating that Galileo's misnamed "lunar seas" may actually have been formed by impacts in ancient lunar seas.

All that aside, there's certainly no hard proof that the ancient Moon had an extensive hydrosphere as Gilvarry proposed. Yet, Saal's and Hauri's water-rich Apollo glass beads may prompt a few scientists to revisit a long lost lunar theory of the 1950s that went out of fashion alongside Detroit's automobile tailfins.

Louis Varricchio, M.Sc., is a former NASA science writer. He is a member of the NASA/JPL Solar System Ambassador program and the Association of Lunar and Planetary Observers.

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