The Sahara sands are 2 to 5 percent water, and the water is tightly bound to the minerals. In the lunar crater, which lies in perpetual darkness, the water is in the form of almost pure ice grains mixed in with the rest of the soil, and is easy to extract. The ice is about 5.6 percent of the mixture, and possibly as high as 8.5 percent of it, Dr. Colaprete said.

“That is a large number, larger than I think anyone was anticipating,” Dr. Colaprete said.

The $79 million Lcross mission piggybacked on the Lunar Reconnaissance Orbiter, which was launched in June last year and has been mapping out the lunar surface for a future return by astronauts. Lcross steered the empty second stage of the rocket, which otherwise would have just burned up in the Earth’s atmosphere, onto a collision course with the Moon.

Last October, as it neared impact, the Lcross spacecraft released the empty second stage and slowed down slightly so that it could watch the stage’s 5,600-mile-per-hour crash into a 60-mile-wide, 2-mile-deep crater named Cabeus. A few minutes later, Lcross, quickly transmitting its gathered data to Earth, met a similar demise.

For people who watched the live Webcast video transmitted by Lcross, the event was a disappointment, with no visible plume from the impacts. But as they analyzed the data, scientists found everything they were looking for, and more. Last November, the team reported that the impact had kicked up at least 26 gallons of water, confirming suspicions of ice in the craters.

The new results increase the water estimate to about 40 gallons, and by estimating by amount of dirt excavated by the impact, calculated the concentration of water for the first time.