Water on the Moon

In 2009, NASA made a startling announcement: water had been found on the supposedly parched moon. And there wasn't a little bit of water in isolated craters, but there was substantial amount of it spread across the surface.

It was a stunning discovery that overturned a decades-old scientific consensus about our nearest celestial neighbor. It also excited the imaginations of scientists and entrepreneurs alike, who saw the life-giving water as making it easier to establish scientific bases, human colonies and mining operations.

The discovery of water on the moon is a fascinating detective story. The six Apollo missions that landed there between 1969 and 1972 brought back hundreds of pounds of moon rocks for scientific study. Researchers who examined the samples detected trace amounts of water in the samples, but they assumed this was the result of contamination on Earth.

The consensus: the Moon was as bone dry as it looked. Some scientists held out hope that water ice might exist in shaded craters at the south pole that never see sunlight. Since the Apollo astronauts did not explore those areas, further investigation was required.

In 1994, the American Clementine orbiter detected what scientists believed was a lake-sized ice deposit in a permanently shaded area of the moon. However, later study using the ground-based Arecibo radio telescope cast doubt on the finding.

Four years later, NASA's Lunar Prospector orbiter used a neutron spectrometer to measure the amount of hydrogen in the lunar rock near the moon's poles. It found hydrogen in abundance, but scientists were unable to confirm whether this was an indication of water ice or the presence of hydroxyl radicals chemically bound to minerals.

Later lunar flybys by two U.S. spacecraft – Cassini-Huygens on its way to Saturn, and Deep Impact headed for comet 103P/Hartley 2 – provided more evidence for the lunar water theory but did not confirm it.

In late 2008, India launched its first lunar orbiter, Chandrayaan-1, with the NASA supplied Moon Mineralogy Mapper (M3) aboard. M3 detected tell-tale wavelengths indicating water on the surface. The data were collaborated by measurements taken by NASA's Lunar Reconnaissance Orbiter (LRO), which entered orbit in 2009.

Water on the Moon Mapped by M3

Moon Mineralogy Mapper generated image of water on the moon.

The Atlas rocket that launched LRO also sent a secondary payload to the moon to look for water. The Lunar CRater Observation and Sensing Satellite (LCROSS) was attached to the rocket's Centaur upper stage, which was sent on a collision course with the lunar south pole. The LCROSS satellite separated from the upper stage prior to impact and recorded the Centaur as it slammed into the Cabeus crater.

The Centaur impact threw up an enormous cloud of debris. In looking at the data collected, scientists were able to confirm the presence of a large amount of water in the shaded crater.

So where did the water come from? Scientists are exploring several theories. One is that comets deposited it over millions of years. Another is that it results from the interaction between the solar wind and the lunar surface. If charged hydrogen atoms in the wind hit the lunar surface hard enough, they would break apart oxygen bound up in the lunar soil. The hydrogen and oxygen then combine to form water.

Regardless of where it came from, the water on the moon awaits the arrival of people to use it and begin a new chapter in human history.

Links for water on the moon

LCROSS mission page

LRO mission page

 

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