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."
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.
This schematic shows the daytime cycle of hydration, loss and rehydration on the lunar surface. In the morning, when the moon is cold, it contains water and hydroxyl molecules. One theory holds that the water and hydroxyl are, in part, formed from hydrogen ions in the solar wind. By local noon, when the moon is at its warmest, some water and hydroxyl are lost. By evening, the surface cools again, returning to a state equal to that seen in the morning. Thus, regardless of location or terrain type, the entire surface of the moon is hydrated during some part of the lunar day. This theory is based on data from NASA's Deep Impact mission.
Credit: University of Maryland/McREL
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Observations from NASA's Deep Impact mission of the moon's north pole from June 2 to 9, 2009 reveal changes in the amounts of water and hydroxyl. In the week between these datasets, the moon had rotated 90 degrees (one-quarter of a lunar day). For example, a volcanic mare terrain (labeled 'M') is observed in the morning on June 2, but by June 9 is at local noon. Similarly, a highland unit ('H') begins at noon and rotates to evening on June 9.
Deep Impact observed a significant change in the strength of a water and hydroxyl signature as the moon rotated around. The highland unit, for example, has a weaker signal near noon (red) and a stronger signal by evening (blue). Taken together, the data show a systematic change in water loss from morning to noon, recovery through the afternoon, and a return to a steady state by evening. This daytime cycle suggests that hydrogen ions in the solar wind may be a source for re-hydration.
Credit: NASA/JPL-Caltech/University of Maryland
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This chart highlights observations from NASA's Deep Impact mission of the northern polar regions of the moon acquired on June 9, 2009. The image at left is a map of the moon taken by the U.S. Clementine satellite -- the rest of the images are different representations of Deep Impact data, including measurements of brightness, temperature, and strength of a signature for water and hydroxyl molecules. The water signature varies significantly across the lunar surface; the strength of the signature is not correlated with terrain type but is highly dependent on temperature.
Credit: NASA/JPL-Caltech/University of Maryland
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Since successfully carrying out its spectacular impact experiment at comet Tempel 1 on July 4, 2005, the Deep Impact spacecraft has been on an extended mission, called Epoxi, which culminates in a flyby of comet Hartley 2 on November 4, 2010. En route to the second comet, the spacecraft observed the moon for calibration purposes on several occasions. In June 2009, the northern polar regions were observed and detailed measurements of light from the regions, called spectra, were collected (blue and cyan). These data unambiguously show the signature of water and hydroxyl (hashed regions). The water signature varies in strength; in particular, data acquired over the warm equator in December 2007 have a distinct but weaker signature (purple).
Credit: NASA/JPL-Caltech/University of Maryland
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These images show a 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 infrared brightness. On the right, the abundance of water (light blue) and hydroxyl (red) is shown around a small crater. Hydroxyl-rich materials are seen as two rays emanating from the crater at the one and seven o'clock positions. Water-rich materials encircle the crater. Ray patterns such as those containing the hydroxyl usually indicate that materials have been excavated from below the surface. If so, it is possible that there are deposits of water- and hydroxyl-rich materials just below the surface of the moon.
Credit: ISRO/NASA/JPL-Caltech/USGS/Brown Univ.
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.
Credit: ISRO/NASA/JPL-Caltech/USGS/Brown Univ.
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This graph compares detailed measurements of light from the moon, called spectra, taken by the Visual and Infrared Mapping Spectrometer (VIMS) on NASA' Cassini spacecraft and NASA's Moon Mineralogy Mapper instrument on the Indian Space Research Organization's Chandrayaan-1 spacecraft. The agreement between the two spacecraft is an excellent confirmation of the existence of water and hydroxyl (gray regions on the graph where wavelengths of infrared light range from 2.7 to 3.2 micrometers). The red dashed lines show the thermal emission, or heat, from the moon, which must be removed to better see the signature of water. The solid lines are the spectra after this thermal emission was removed.
Credit: NASA/ISRO/JPL-Caltech/USGS/Brown Univ.
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NASA's Cassini spacecraft observations of the moon on Aug. 19, 1999 show water and hydroxyl at all latitudes on the surface, even areas exposed to direct sunlight. The Visual and Infrared Mapping Spectrometer (VIMS) instrument on Cassini made the observations as the spacecraft flew by the moon. Its view was slightly south of the lunar equator. The yellow cross indicates a latitude and longitude of zero.
The picture at top left shows infrared light reflected off the moon as seen by VIMS. The top right picture shows the moon as seen by Cassini's Imaging Science Sub-system (ISS) during the flyby. The image at bottom left shows temperatures of the moon derived from VIMS data. Temperatures near the equator are hotter than boiling water on Earth. The bottom center picture shows a VIMS map of water associated with minerals. At bottom right is a VIMS map of hydroxyl-bearing minerals, created by chemical reactions with minerals and glasses in the lunar soil.
Credit: NASA/JPL-Caltech/USGS
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This is an early mineral map derived from the different reflected light, or spectral, signatures, measured by NASA's Moon Mineralogy Mapper on board the Indian Space Research Organization's Chandrayaan-1 spacecraft. The green, purple and blue areas are covered with iron-rich lava flows. These are similar to the lava flows of Hawaii. The red and pink regions contain the mineral plagioclase. Plagioclase is one of the minerals found in granite rocks on Earth, such as the granite of Yosemite National Park.
Credit: ISRO/NASA/JPL-Caltech/Brown Univ.
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On the left, a portion of the first image cube measured by NASA's Moon Mineralogy Mapper on board the Indian Space Research Organization's Chandrayaan-1 spacecraft on Nov. 19, 2008 shows the crater Harpalus north of Mare Imbrium. The rainbow-colored panels to the top and right of each image represent the different reflected light, or spectral, signatures that underlie every point in the image. These signatures allow determination of the surface composition. The image cube on the right was measured on Feb. 5, 2009 and includes the Apollo 15 landing site adjacent to the feature Hadley Rille.
Credit: ISRO/NASA/JPL-Caltech/Brown Univ.
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Many small, fresh craters bear signatures of water and hydroxyl, which are detected as absorptions of infrared light in the range of 3 micrometers by NASA's Moon Mineralogy Mapper. Figure A, on the left, shows feldspar-rich terrain on the side of the moon facing away from Earth. The arrows point to the location of small, fresh craters. Figure B, on the right, indicates the reflectance as a function of wavelength for craters in Figure A. The water and hydroxyl signature in these regions is seen as a characteristic dip in reflectance in the infrared light near the 3-micrometer range, a region noted with a light-blue band. The dashed line shows background soil that doesn't contain significant water or hydroxyl.
Credit: ISRO/NASA/JPL-Caltech/Brown Univ.
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These images from NASA's Moon Mineralogy Mapper on the Indian Space Research Organization's Chandrayaan-1 spacecraft show data for the hemisphere of the moon that faces Earth. The image on the left shows albedo, or the sunlight reflected from the surface of the moon. The image on the right shows where infrared light is absorbed in the characteristic manner that indicates the presence of water and hydroxyl molecules. That image shows that signature most strongly at the cool, high latitudes near the poles. The blue arrow indicates Goldschmidt crater, a large feldspar-rich region with a higher water and hydroxyl signature.
Credit: ISRO/NASA/JPL-Caltech/Brown Univ.
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This image of the moon is from NASA's Moon Mineralogy Mapper on the Indian Space Research Organization's Chandrayaan-1 mission. It is a three-color composite of reflected near-infrared radiation from the sun, and illustrates the extent to which different materials are mapped across the side of the moon that faces Earth.
Small amounts of water and hydroxyl (blue) were detected on the surface of the moon at various locations. This image illustrates their distribution at high latitudes toward the poles.
Blue shows the signature of water and hydroxyl molecules as seen by a highly diagnostic absorption of infrared light with a wavelength of three micrometers. Green shows the brightness of the surface as measured by reflected infrared radiation from the sun with a wavelength of 2.4 micrometers, and red shows an iron-bearing mineral called pyroxene, detected by absorption of 2.0-micrometer infrared light.
Credit: ISRO/NASA/JPL-Caltech/Brown Univ./USGS
"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."
