Discovery Made In The Polar Regions, But May Be More
Pervasive
NASA scientists 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. The findings were published in Thursday's
edition of the journal Science.
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," said Jim Green, director of
the Planetary Science Division at NASA Headquarters in Washington.
"This surprising finding has come about through the ingenuity,
perseverance and international cooperation between NASA and the
India Space Research Organization."
Chandrayaan 1 Vehicle
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 are typically attributed to
water and hydroxyl-bearing materials," said Carle Pieters, M3's
principal investigator from Brown University, Providence, R.I.
"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,"
said 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."
For additional confirmation, scientists turned to the Epoxi
mission while it was flying past the moon in June 2009 on its way
to a November 2010 encounter with comet Hartley 2. The spacecraft
not only confirmed the VIMS and M3 findings, but also expanded on
them.
"With our extended spectral range and views over the north pole,
we were able to explore the distribution of both water and hydroxyl
as a function of temperature, latitude, composition, and time of
day," said Jessica Sunshine of the University of Maryland. Sunshine
is Epoxi's deputy principal investigator and a scientist on the M3
team. "Our analysis unequivocally confirms the presence of these
molecules on the moon's surface and reveals that the entire surface
appears to be hydrated during at least some portion of the lunar
day."