An artist's impression of the Centaur upper stage detaching from the LCROSS spacecraft. (credit: NASA)

It was time for the spent rocket to die. So the 2,000kg Centaur upper stage, about the size of a yellow school bus, detached from its spacecraft and began falling toward the Moon six years ago. Soon lunar gravity took hold, tugging the Centaur ever faster toward the Moon’s inky black South Pole. An hour after separation, the rocket slammed into terra incognita at 9,000kph (or roughly 5,600mph).

Named for a mythical creature with the upper body of a human and lower body of a horse, the empty Centaur burrowed several meters into a crater that had not seen the Sun’s light for billions of years. The impact kicked a plume of Moon dust as high as 20 km into space. The detached spacecraft followed just minutes later, sampling the plume. “We knew within hours that we had measured something really interesting,” recalled Anthony Colaprete, the mission’s principal investigator.

Interesting indeed. After more than a decade of speculation and intriguing findings, the Centaur had blasted up grains of pure ice. It provided dazzling confirmation that a world once thought entirely barren and desiccated harbors the most valuable commodity for human exploration—water. Yet even as Colaprete and other scientists announced their findings in the fall of 2009, NASA’s lunar program was dying.

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