However, Urey believed that any ice in these sunless locations would have been “rapidly lost” because of the moon’s lack of atmosphere. This means the sun’s rays strike its poles nearly horizontally, and the rims of polar craters will block light from directly reaching their depths. He observed that, whereas Earth orbits the sun with its rotational axis tilted by 23.5 degrees, the moon orbits at a mere 1.5-degree tilt. “Near its poles there may be depressions on which the sun never shines,” he wrote. Speculation about PSRs dates back to 1952, when the American chemist Harold Urey first hypothesized their existence on the moon. “That’s the coolest thing.” Water, Water, Everywhere “I don’t know what we’re going to see,” said Robinson, the lead scientist for next year’s robotic mission. What will we find lurking in the shadows? On the eve of this new era of moon landings, a slew of fresh studies of PSRs have revealed that these shadowed regions are even stranger than scientists imagined. By the decade’s end, NASA plans to send humans to explore in person. Next year, robotic vehicles will enter the bewildering icy depths of PSRs for the first time, revealing what the interiors of these shadowed craters look like. Studies so far have provided a tantalizing glimpse at best.
It could also be a resource for future human activities on the moon. Studying the ice’s chemical composition should reveal how it was delivered to the moon, in turn illuminating the origin of water on Earth, or indeed any rocky world around any star. This means ice on or below the lunar surface in PSRs won’t necessarily melt instead it might have survived there for billions of years. “Some PSRs are colder than the surface of Pluto,” said Parvathy Prem, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Maryland. Inside, temperatures can drop below minus 170 degrees Celsius. PSRs are of immense interest to scientists.
“They’re in permanent darkness,” said Valentin Bickel, a planetary scientist at the Max Planck Institute for Solar System Research in Germany. These are craters like Cabeus into which the sun can’t reach, because of the geometry of the moon’s orbit. Most of this ice resides in peculiar features at the moon’s poles called permanently shadowed regions (PSRs). Scientists now think there’s not just a bit of water ice on the moon there are 6 trillion kilograms of it. Yet about 25 years ago, spacecraft began to detect signatures of hydrogen around the moon’s poles, hinting that water might be trapped there as ice. Its lack of atmosphere and extreme temperatures should cause any water to almost instantly evaporate. “It’s really weird when you stop to think about it,” said Mark Robinson, a planetary scientist at Arizona State University. The moon isn’t an obvious reservoir of water. “It was absolutely definitive,” said Anthony Colaprete of NASA’s Ames Research Center, the principal investigator of LCROSS. They had, for the first time, found water on the moon. The results of the experiment were astonishing: Scientists detected 155 kilograms of water vapor mixed into the dust plume. A spacecraft trailing the rocket flew through the dust plume to sample it, while NASA’s Lunar Reconnaissance Orbiter observed from afar. NASA’s Lunar Crater Observation and Sensing Satellite (LCROSS) mission aimed to see what would be kicked up from the lunar shadows by the impact. As it exploded in a shower of dust and heated the lunar surface to hundreds of degrees, the jet-black crater into which it plummeted, called Cabeus, briefly filled with light for the first time in billions of years.
On October 9, 2009, a two-ton rocket smashed into the moon traveling at 9,000 kilometers per hour.
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