Welcome to Quantum Magazine's podcast. Each episode, we bring you stories about developments in science and mathematics. I'm Susan Vallett. On October 9th, 2009, a two-ton rocket smashed into the moon, traveling at 9,000 kilometers per hour.

It exploded in a shower of dust and heated the lunar surface to hundreds of degrees.

The jet black crater into which it plummeted, briefly filled with light for the first time

in billions of years.

The crash was no accident.

NASA's Lunar Crater Observation and Sensing Satellite, or El Cross mission, aimed to see

what would be kicked up from the lunar shadows by the impact. Why? That's next.

If you like this podcast, check out The Joy of Why, hosted by me, Steve Strogettz,

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We ask questions like, why can prolonged sleep deprivation ultimately be fatal?

Where do space, time, and gravity come from? What is life? Learn about all that and more on the joy of why, wherever you get your podcasts.

As part of the El Cross mission, a spacecraft flew through the kicked up dust plume from Cabez's crater to sample it.

NASA's lunar reconnaissance orbiter observed from afar.

The results of the experiment were astonishing.

Scientists detected 155 kilograms of water vapor mixed into the dust plume.

For the first time, they'd found water on the moon. Tony Colopreet of NASA's Ames Research Center,

the principal investigator of Elcross, says it was absolutely definitive. The moon isn't an

obvious reservoir of water. Here's Mark Robinson, a planetary scientist at Arizona State University.

It's really weird when you stop to think about it that there could be water on the surface of the

moon or on the regulars because it's a vacuum. The moon gets super hot during the day and freezing

cold at night. And now you've got this weird environment that's permanently shadow,

which is kind of a foreign concept to Earthlings,

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