The icy poles

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.”