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Joe Bauman
This telescopic image from Oct. 9, 2009, shows the oon's south pole at the time that a rocket motor and an instrument package crashed into the vicinity in a search for signs of water. The experiment detected nearly pure ice as well as water that was mixed with chemicals. The huge crater toward the bottom middle is named Clavius; it is 146 miles across.

Editor's note: A version of this was previously published on the author's website.

NASA’s long-term goals changed on Dec. 11, 2017, shifting from human exploration of asteroids to a return to the moon.

The 2010 version of the National Space Policy contained these instructions: "Set far-reaching exploration milestones. By 2025, begin crewed missions beyond the moon, including sending humans to an asteroid. By the mid-2030s, send humans to orbit Mars and return them safely to Earth. …"

In his Space Policy Directive 1, President Donald Trump removed that section and replaced it with: "Lead an innovative and sustainable program of exploration with commercial and international partners to enable human expansion across the solar system and to bring back to Earth new knowledge and opportunities. Beginning with missions beyond low-Earth orbit, the United States will lead the return of humans to the Moon for long-term exploration and utilization, followed by human missions to Mars and other destinations. …"

Titled "Reinvigorating America’s Human Space Exploration Program," the policy is addressed to everyone in the executive branch who might have a hand in implementing it, from Vice President Mike Pence to the NASA administrator, from the chairman of the Joint Chiefs of Staff to the secretaries of commerce, defense and state. The impression is that the directive must be followed up.

To a space and astronomy advocate old enough to remember the first moon landing on July 20, 1969, nothing could be more exciting than the prospect of going back to our natural satellite. It even outshines Mars as a destination because a permanent base could be established on the moon to carry out astronomical studies that would be of incalculable scientific worth.

Imagine a base with a live-in staff and an immense telescope operating without Earth's atmospheric distortions or the engineering constraints imposed by our six-times-heavier gravity. A gigantic mirror array on the far side of the moon would open astonishing vistas. Although every lunar month it would be subjected to 14 straight days of daylight (as well as an equal length of night), the Earth wouldn't intrude to block any of the cosmos.

Also on the side away from Earth, radio astronomy would thrive, as an observatory there would remain in Earth's radio shadow. Presently, radio observations are limited, and sometimes confused, by terrestrial interference. The same advantage of engineering scale would apply to radio astronomy because gravity wouldn't weigh down the vast receivers as badly as it does here.

The moon remains a mysterious and strange world, one whose resources aren't fully known. But one resource that could be essential to a base, water, is present. Reservoirs of water ice, which obviously could be mined and melted, remain in the permanent shadows of some craters.

As a 2013 report filed by NASA's Lunar and Planetary Institute says (in a shaky translation from what must be the original Chinese), "It is concluded that the water in many kinds of formation like water ice with a few meters thick buried by a thin (a few cm) regolith is deposited at cold traps in permanently shadowed region at lunar poles. The water ice originated by solar wind, comets impacts or other unknown reasons." The authors are Hongwei Yang, Wenjin Zhao and Zhenhan Wu of the Chinese Academy of Geological Sciences, Beijing.

Earlier studies using remote sensing indicated the presence of water. But the most dramatic proof came with NASA's Lunar Reconnaissance Orbiter and Lunar Crater Observation and Sensing Spacecraft project. These temporary lunar satellites not only studied the moon from orbit, but in the early morning of Friday, Oct. 9, 2009, NASA crashed the upper stage of the Centaur rocket and the LCROSS instrument package into a small crater at the south pole.

The crater bottom had been hidden in shadow, presumably for billions of years, where ice would not have melted from the heat of the sun. The impacts were to kick up plumes of material that were examined by spectroscopy to determine their makeup.

First the rocket stage impacted, with LCROSS and the orbiter examining the debris. Then it was LCROSS' turn, leaving the Reconnaissance Orbiter to check its plume. Unfortunately for those who shivered in the predawn cold to watch through telescopes, no plume was visible to Earth-bound observers. But the spacecraft detected the plumes rising 10 miles above the crater rim.

A little more than a year following the crashes, NASA announced the project "found evidence that the lunar soil within shadowy craters is rich in useful materials, and the moon is chemically active and has a water cycle. Scientists also confirmed the water was in the form of mostly pure ice crystals in some places." Also discovered were minerals including sodium, mercury and possibly silver.

Volatile compounds that would evaporate in sunlight — "methane, ammonia, hydrogen gas, carbon dioxide and carbon monoxide" — made up as much as 20 percent of the dust that was kicked up.

The best news was, "After the impacts, grains of mostly pure water ice were lofted into the sunlight in the vacuum of space," NASA added. That indicates astronauts should be able to refine the water for human use.

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In 2013, the Jet Propulsion Laboratory released a statement that it had "evidence of water locked in mineral grains on the surface of the moon from an unknown source deep beneath the surface." The release was based on a paper reviewing data from a 2009 project. The NASA Moon Mineralogy Mapper instrument was carried by an Indian spacecraft called Chandrayaan-1 and the discovery was made by mapping a crater near the equator. The region is regularly blasted by sunlight, unlike the perpetually shadowed site near the south pole.

How much usable water is locked in dark craters or mineral grains on the moon? It's a subject for further studies, but the indications are promising.

Almost 50 years after our first moon landing, it's time to go back.