Scientists
at the National Aeronautics and Space Administration (NASA) have discovered
water molecules in the polar regions of the moon. Instruments aboard three
separate spacecraft revealed water molecules in amounts that are greater than
predicted, but still relatively small. Hydroxyl, a molecule consisting of one
oxygen atom and one hydrogen atom, also was found in the lunar
soil.
NASA’s Moon Mineralogy Mapper, or M3, instrument reported the observations. M3
was carried into space on Oct. 22, 2008, aboard the Indian Space Research
Organization’s Chandrayaan-1 spacecraft. Data from the Visual and Infrared
Mapping Spectrometer, or VIMS, on NASA’s Cassini spacecraft and the
High-Resolution Infrared Imaging Spectrometer on NASA’s EPOXI spacecraft
contributed to confirmation of the finding. The spacecraft imaging
spectrometers made it possible to map lunar water more effectively than ever
before.
The confirmation of elevated water molecules and hydroxyl at these
concentrations in the moon’s polar regions raises new questions about its
origin and effect on the mineralogy of the moon. Answers to these questions
will be studied and debated for years to come.
“Water ice on the moon has been something of a holy grail for lunar scientists
for a very long time,” says Jim Green, director of the Planetary Science
Division at NASA. “This surprising finding has come about through the
ingenuity, perseverance and international cooperation between NASA and the
India Space Research Organization.”
From its perch in lunar orbit, M3’s state-of-the-art spectrometer measured
light reflecting off the moon’s surface at infrared wavelengths, splitting the
spectral colors of the lunar surface into small enough bits to reveal a new
level of detail in surface composition. When the M3 science team analyzed data
from the instrument, they found the wavelengths of light being absorbed were
consistent with the absorption patterns for water molecules and hydroxyl.
“For silicate bodies, such features typically are attributed to water and
hydroxyl-bearing materials,” explains Carle Pieters, M3’s principal
investigator from Brown University. “When we say ‘water on the moon,’ we are
not talking about lakes, oceans or even puddles. Water on the moon means
molecules of water and hydroxyl that interact with molecules of rock and dust
specifically in the top millimeters of the moon’s surface.”
The M3 team found water molecules and hydroxyl at diverse areas of the sunlit
region of the moon’s surface, but the water signature appeared stronger at the
moon’s higher latitudes. Water molecules and hydroxyl previously were suspected
in data from a Cassini flyby of the moon in 1999, but the findings were not
published until now.
“The data from Cassini’s VIMS instrument and M3 closely agree,” says Roger
Clark, a U.S. Geological Survey scientist in Denver and member of both the VIMS
and M3 teams. “We see both water and hydroxyl. While the abundances are not
precisely known, as much as 1,000 water molecule parts-per-million could be in
the lunar soil. To put that into perspective, if you harvested one ton of the
top layer of the moon’s surface, you could get as much as 32 ounces of water.”