Water appears to be more common on the moon than previously thought, raising hopes of a viable human colony and further exploration.
NASA last week said it had made an "exciting new discovery", prompting a flurry of speculation - most of it light-hearted, with suggestions scientists had discovered it is indeed made of cheese or - predictably - that it had found aliens.
After five days of fevered anticipation, the space agency on Tuesday morning (NZ time) revealed what it's found - confirmation that previously detected molecules containing hydrogen and oxygen are indisputably water, and in certain places, quite possibly abundant.
"Whereas before we saw signatures that 'might' be water, that has now been confirmed as definitely water," said Andrew Dempster, director of the Australian Centre for Space Engineering Research.
The findings came in two studies. The first was conducted by Casey Honniball, a postdoctoral fellow at NASA's Goddard Space Flight Center, using data collected by the Stratospheric Observatory for Infrared Astronomy (SOFIA), a Boeing 747 which flies in the stratosphere - often taking off from Christchurch - with an onboard telescope.
Previous scans of the moon had found evidence of water, but couldn't tell the difference between water and other molecules containing hydrogen and oxygen, known as hydroxyls. The new scan, done on August 31, 2018, was at a frequency which could tell them apart.
They found water is definitely there, particularly around the poles. While some is brought in by meteorites, most of the water appears to largely be created on the moon's surface - sometimes hydroxyls are turned into water in high-energy collisions from incoming meteorites, other times from the sheer 100C-plus temperature of the midday sun.
"Our results are more consistent with the existence of a mechanism that produces water by impact from pre-existing lunar material," Dr Honniball and colleagues wrote in their new study, published in journal Nature Astronomy.
"A majority of the water we detect must be stored within glasses or in voids between grains sheltered from the harsh lunar environment, allowing the water to remain on the lunar surface."
And just how much water there is is revealed in a second paper, also published in Nature Astronomy on Tuesday.
Scientists used data from the Lunar Reconnaissance Orbiter, in orbit around the moon, to map how much of the lunar surface is permanently in shadow. These 'cold traps' where the sun never shines could store water undisturbed for millions of years.
Paul Hayne of the University of Colorado Boulder and colleagues found there could be thousands of cold traps on the moon, ranging in size from 1cm to more than a kilometre across.
All-up, they estimate at least 40,000 square kilometres of the lunar surface could potentially hold water. Most of the traps are around the poles, which is where Dr Honniball's team detected the most water.
"These findings indicate that water is efficiently produced or delivered on the Moon by various processes, and is likely to be stored in the Moon's cold traps at both polar regions," Springer Nature, the publisher of the journal, said in a statement.
"The presence of water may have implications for future lunar missions targeting and accessing these potential ice reservoirs."
Why it's a big deal
That the findings relate to water might disappoint those hoping for aliens, but there's a good reason NASA is excited.
"Water on the Moon is more than just an exciting scientific discovery, it makes possible the future expansion of humanity into an multi-planet species," said Alan Duffy, astronomer and lead scientist at the Royal Institution of Australia.
"To launch a litre bottle of water from Earth to the Moon costs $35,000 – almost the same cost as if we just made that bottle solid gold. But by accessing it directly from the Moon itself we turn our celestial neighbour into a resupply as well as a refuelling station.
"Water can directly support astronauts on a planned Moon-base, used to grow food on long-duration missions to Mars, and even split into literal rocket fuel for powering our satellites and rockets across the Solar System."
Duncan Steel, a space scientist formerly of NASA and the European Space Agency who currently lives in Nelson, correctly predicted last week the discovery would relate to one of the the most abundant substances on Earth.
"We are mainly interested in water on the moon due to the need for it for human presence there: we would use the water for the usual purposes (drinking, showering), but also H2O is obviously a good source of oxygen, which we need to breathe," "On top of that, the H2O could be split so as to make rocket propellant."
Water on the moon typically exists as ice - liquid water doesn't exist in a vacuum, ice going straight to water vapour when it's heated in a process known as sublimation.
"If water is the oil of space, the Moon just became the OPEC of orbital refuelling," said Prof Duffy.
Dr Steel even predicted where the water would be found: "likely in the surface structure or as hydrated minerals".
"This is important for human exploration/establishing a scientific outpost there."
NASA plans to send humans back to the moon in 2024, including the first woman, as part of its Artemis programme. Mars is hoped to be next, sometime in the 2030s.