Lunar Trailblazer Launches to Map Water on the Moon's Surface, Shaping Future Lunar Colonisation Plans

On Thursday, a SpaceX Falcon rocket is due to lift off from Florida carrying a probe built by researchers in the UK and the US. The probe is Lunar Trailblazer, and its job over a two-year mission is to map water on the surface of the moon, a body long thought to be bone dry.

The idea is less strange than it once sounded. For years the working assumption was that water molecules delivered to the moon by meteorites and comets would not last. Sunlight would break them into hydrogen and oxygen, and those elements would drift off into space. That view has been eroded by several robotic probes, which have found strong evidence of water, mostly as ice, in fairly large amounts inside deep, permanently shadowed craters. The lunar south pole offers the most promising candidates.

India's Chandrayaan-1 probe pushed the picture further in 2009, when it detected traces of water on the surface far from the poles. Prof Neil Bowles, who leads the Oxford University team of physicists that built one of Lunar Trailblazer's main instruments, called it a big surprise that changed perceptions of what might be found on the moon. But the instrument that made the discovery lacked the spectral range to map the water fully, and Lunar Trailblazer was designed to get around that limit.

It carries two instruments. The first is an infrared scanner that will pinpoint water and other geological features. The second, designed by Bowles and his team, is a thermal mapper, essentially a highly advanced heat camera. Working together, they should produce a water map of the lunar surface.

The open question is how the water got where it is. Bowles says water is known to exist at the poles, but not how it arrived. He describes a kind of lunar water cycle, though one with nothing to do with clouds or rain. In one scenario, comets or meteorites strike the surface and release a lot of water, which then condenses in cold traps at the poles. In the other, very thin layers of water form through reactions in the lunar soil. Neither explains how the water moves around and builds up into ice deposits, which is what the team wants to learn. The answer matters beyond the moon, Bowles says, since it bears on similar worlds such as Mercury.

There is a practical side too. Space engineers and astronomers will watch the mission closely because lunar water could be central to plans for staffed colonies. Powered by solar plants, water could be split into hydrogen and oxygen, the first for fuel and the second for astronauts to breathe. Bowles stresses that this is primarily a scientific mission, but says it should also reveal how water is transported across the surface, which has implications for human exploration.

Lunar Trailblazer will not fly alone. The launch also carries the rocket's main payload, IM-2, a lunar lander built by the US company Intuitive Machines, which is meant to settle on the moon and drill beneath the surface in search of water. A third craft, a probe called Odin from the company AstroForge, is headed for asteroid 2022 OB5. It will take images in preparation for a return mission that would land on the asteroid and begin extracting minerals from its surface.

All of these flights belong to NASA's commercial lunar payload services programme, which encourages companies to send small robotic landers and rovers to the moon and other near-Earth destinations. Its stated main aim is to prepare for the eventual colonisation of the moon. What Lunar Trailblazer's map shows over the next two years will help decide where that preparation points.