Going through a phase

What accounts for our current obsession with the moon? We’ve found evidence of water in sunlit spots, got new views of the ‘dark side’. Amid growing interest in its rare minerals, there are plans for humans to return. How close are we to permanent bases? And where do the Chandrayaan missions fit in? Take a look

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Scientists have long suspected that there might be water on the moon. A number of asteroids and comets carry water ice, and even today the theory is that the water on the moon got there via these bodies.

But for decades, no one knew where to look. In 1996, the NASA lunar orbiter Clementine sent home the first hints: data indicating the signature of water ice at the poles. Definitive proof came in 2008, via Chandrayaan-1. India’s first moon mission, an orbiter, took off carrying, among other things, two instruments provided by NASA for the express purpose of surveying the poles for water ice. They found the signatures they were looking for, in more than 40 craters. There was no longer any doubt; wherever the water may have come from, it’s there now. “More water is likely concentrated in the craters at the poles because they don’t receive any sunlight,” says Anil Bhardwaj, astrophysicist and director of the Physical Research Laboratory, Ahmedabad. Elsewhere on the low-pressure moon, where daytime temperatures reach 120 degrees Celsius, water would be vapourised.

Meanwhile, in 2020, data from NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) found the first evidence of water in a sunlit spot, indicating that these precious molecules are more widely distributed than previously thought.

“Without a thick atmosphere, water on the sunlit lunar surface should just be lost to space,” Casey Honniball, a postdoctoral fellow at NASA’s Goddard Space Flight Center, said in a press release. “Yet somehow we’re seeing it.

Something is generating the water, and

something must be trapping it there.” pole (right), as detected by NASA’s Mo Mineralogy Mapper on Chandrayaan-1. The blue indicates the locations of the i The greys correspond to surface temperature, with the darker shades representing colder areas.

NASA / GODDARD SPACE FLIGHT CENTER / ARIZONA STATE UNIVERSITY Images of the far side of the moon (above right) show a vastly different landscape — pitted with craters, and with none of the dark volcanic plains so familiar to us on the near side (above).

NASA