IS THE MOON GETTING MORE WATER?

Lunar water was a myth before it was a mystery. Like Earth, the Moon formed on the wrong side of the Solar System’s snow line, the imaginary boundary beyond which water ice was available for planetary assembly. Later, the exposed, Sun-scorched surface of our atmosphereless Moon continued to provide a hostile environment for water. It’s perhaps unsurprising that when samples brought back by the Apollo missions were shown to contain trace amounts of the stuff, the verdict was terrestrial contamination.

However, in the 1990s, two NASA orbiters, Clementine and Lunar Prospector, provided strong hints of surface water at the poles. This was confirmed by a series of landmark papers in 2009 analysing data from three missions: India’s Chandrayaan-1 orbiter, Cassini’s flyby on its way to Saturn and NASA’s EPOXI spacecraft. The high-latitude reservoirs of ‘dirty ice’ buried in the lunar soil were vast in scale. A 2010 analysis led by the Lunar and Planetary Institute’s Paul Spudis using Chandrayaan-1’s radar data estimated as much as 600 million tonnes of water ice could be locked up in just 40 locales around