Photos: The Search for Water on the Moon

In July 2008, water was found conclusively for the first time inside ancient moon samples brought back by Apollo astronauts. Researchers led by Brown geologist Alberto Saal analyzed lunar volcanic glasses, such these gathered by the Apollo 15 mission, and used a new analytic technique to detect water. The discovery strongly suggests that water has been a part of the Moon since its early existence – and perhaps since it was first created.

Many experts were shocked by the 2009 discovery of water on the moon, which was long thought to be bone-dry. These images show a very young lunar crater on the side of the moon that faces away from Earth, as viewed by NASA's Moon Mineralogy Mapper on the Indian Space Research Organization's Chandrayaan-1 spacecraft. On the left is an image showing brightness at shorter infrared wavelengths. On the right, the distribution of water-rich minerals (light blue) is shown around a small crater. Both water- and hydroxyl-rich materials were found to be associated with material ejected from the crater.

In 2009, observations from three spacecraft showed signals of water across moon's surface. This illustration shows the stream of charged hydrogen ions carried from the sun to the moon by the solar wind. Scientists think this process might explain the possible presence of hydroxyl or water on the moon.

NASA's Mini-SAR instrument, which flew aboard India's Chandrayaan-1 spacecraft, found more than 40 small craters with water ice. The craters range in size from 1 to 9 miles (2 to 15 km) in diameter. Although the total amount of ice depends on its thickness in each crater, it's estimated there could be at least 600 million metric tons of water ice. The red circles denote fresh craters; the green circle mark anomalous craters.

The evidence is building that permanently shadowed craters near the moon's poles hold huge deposits of water ice. This crater is one potential spot.

The Lyman Alpha Mapping Project found that the moon's permanently shadowed regions may hide stores of water ice. This photo of the moon's south pole, taken by NASA's Lunar Reconnaissance Orbiter, shows some of the permanently shadowed regions.

A January 2011 study suggested that water on the moon most likely came from comets that pelted the lunar surface after its formation.

In October 2010, scientists reported that a frigid crater called Cabeus at the moon's south pole is jam-packed with water ice, with some spots wetter than Earth's Sahara desert.

NASA's LCROSS probe discovered beds of water ice at the lunar south pole when it impacted the moon in October 2009. This visible camera image shows the ejecta plume at about 20 seconds after LCROSS's impact on the moon.

A July 2010 study found that the moon's interior may harbor 100 times more water than previous estimates, according to a new study that took a fresh look at samples of moon rocks collected by Apollo astronauts nearly 40 years ago.

Recent studies have found vast amounts of water ice at or near the lunar surface. But the inside of the moon is bone dry, an August 2010 study found.

Permanently shadowed craters at the lunar poles, called "cold traps," might be repositories of water ice. The U.S. Clementine probe gathered data about the moon’s poles in 1994. In these composite maps, areas in permanent darkness are black, while areas of permanent illumination are white; areas of mixed lighting condition are represented in various shades of gray. Note that the south polar area has the largest area of permanent darkness. Several areas are evident that have near-constant sun illumination.