Deep Impact And Other Spacecraft Find Clear Evidence Of Water On Moon
Deep Impact And Other Spacecraft Find Clear Evidence Of Water On Moon
by Staff Writers
College Park MD (SPX) Sep 25, 2009
New data from the Deep Impact spacecraft and the Moon Mineralogy Mapper (M3), an instrument aboard India's recently ended Chandrayaan-1 spacecraft, provide, for the first time, clear evidence that water exists on the surface of the Moon.
"The Deep Impact observations of the Moon not only unequivocally confirm the presence of OH/H2O on the lunar surface, but also reveal that the entire lunar surface is hydrated during at least some portions of the lunar day," write University of Maryland astronomer Jessica Sunshine and co-authors in a paper on the Deep Impact data published online in the September 24 issue of the journal Science.
Small Amount of Water Yields Big Excitement
"Finding water on the Moon in daylight is a huge surprise, even if it is only a small amount of water and only in the form of molecules stuck to soil," said Sunshine, lead author of the Deep Impact paper and a co-author of a companion Science paper based on data from the M3 instrument that first detected the presence of lunar water.
Prevailing scientific opinion long has been that there probably is no water on the Moon and that, even if it does exist, it would be only in permanently cold, shadowed craters at the lunar poles.
"In the Deep Impact data we're essentially watching water molecules form and then dissipate right in front of our eyes," said Sunshine, who said her first reaction to the M3 data was skepticism.
"We aren't certain yet how this happens," she said, "but our findings suggest a solar driven cycle in which layers of water only a few molecules thick form, dissipate and reform on the surface each lunar day. We postulate that hydrogen ions from the sun are carried by the solar wind to the Moon and there interact with oxygen rich minerals in lunar soil to produce the water [H20] and hydroxyl [OH] molecules that spectral analysis unequivocally show us are there.
In a cycle that occurs entirely in daylight, this water is formed in the morning, substantially lost by lunar mid-day, and re-formed as the lunar surface cools towards evening.
"If this is correct, then such hydration via solar wind would be expected to occur throughout the inner Solar System on all airless bodies with oxygen-bearing minerals on their surfaces," Sunshine said.
"Within the context of lunar science, this is a major discovery," Paul G. Lucey, a planetary scientist with the University of Hawaii, said in a Los Angeles Times article. "There was zero accepted evidence that there was any water at the lunar surface, [but] now it is shown to be easily detectable, though by extremely sensitive methods. As a lunar scientist, when I read about this I was completely blown away," said Lucey, who was not involved in the current research.
Another reflection of the scientific significance of finding water on the moon was simply that it generated three papers in the current issue of Science and a NASA press conference. In addition to the M3 and Deep Impact articles, a third Science paper presented evidence collected by NASA's Cassini spacecraft.
Lunar H20 Latest in UM-Led Deep Impact Science
Although the M3 instrument and its science team made the initial discovery of water in certain areas of the lunar surface, Sunshine and co-authors on the Deep Impact paper said the conclusiveness of the finding of water, the realization it was a surface-wide phenomenon, and the insight into the temperature dependent nature of the process were only possible because of data collected by the Deep Impact spacecraft during it's current extended mission (EPOXI).
Deep Impact was not designed to study the Moon, but for a famous 2005 mission in which it successfully knocked a hole in comet Tempel 1 to find out what was inside. Its data on lunar water were obtained as part of calibration opportunities that occurred during June 2009 and December 2007 flybys of the Earth and Moon needed to get adequate gravity boosts to travel on its EPOXI mission to a second comet, Hartley 2, which the spacecraft will encounter in November 2010.
"Without the spectral range of Deep Impact's instruments the M3 discovery of surface water would not have been nearly so definitive, and because the Deep Impact spacecraft took observations at different times of the lunar day, the effect of temperature became very apparent," Sunshine explained.
University of Maryland Astronomer Michael A'Hearn, Deep Impact and EPOXI science team leader and one of Sunshine's four Maryland co-authors on the Deep Impact paper in Science, said "I think it is tremendous that the Deep Impact spacecraft, which was the first to detect ice on a cometary nucleus, has now demonstrated the existence of adsorbed water on the Moon. "This great spacecraft and its instruments continue to make important, unexpected discoveries long after the prime mission has ended," he said.
related report
NASA Instruments Reveal Water Molecules On Lunar Surface
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.
"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."
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the M3 instrument, Cassini mission and Epoxi spacecraft for NASA's Science Mission Directorate in Washington. The Indian Space Research Organization built, launched and operated the Chandrayaan-1 spacecraft.
