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No Water Ice Detected From Lunar Prospector Impact

Douglas Isbell
Headquarters, Washington, DC                Oct. 13, 1999
(Phone:  202/358-1547)

David Morse
Ames Research Center, Moffett Field, CA 
(Phone:  650/604-4724)

Becky Rische
University of Texas at Austin
(Phone:  512/471-7272)

RELEASE: 99-119

NO WATER ICE DETECTED FROM LUNAR PROSPECTOR IMPACT

     The controlled crash of NASA's Lunar Prospector 
spacecraft into a crater near the south pole of the Moon 
on July 31 produced no observable signature of water, 
according to scientists digging through data from Earth-
based observatories and spacecraft such as the Hubble 
Space Telescope.

     This lack of physical evidence leaves open the 
question of whether ancient cometary impacts delivered 
ice that remains buried in permanently shadowed regions 
of the Moon, as suggested by the large amounts of 
hydrogen measured indirectly from lunar orbit by Lunar 
Prospector during its main mapping mission.

     Research group leaders from the University of Texas 
at Austin announced their results today at the annual 
meeting of the American Astronomical Society's Division 
for Planetary Sciences meeting in Padua, Italy.

     In a low-budget attempt to wring one last bit of 
scientific productivity from the low-cost Lunar 
Prospector mission, NASA worked with engineers and 
astronomers at the University of Texas to precisely crash 
the barrel-shaped spacecraft into a specific shadowed 
crater.  NASA accepted the team's proposal based on 
successful scientific peer review of the idea and the 
pending end of the spacecraft's useful life, although the 
chances of positive detection of water were judged to be 
less than 10 percent.

     Worldwide observations of the crash were focused 
primarily on using sensitive spectrometers tuned to look 
for the ultraviolet emission lines expected from the 
hydroxyl (OH) molecules that should be a by-product of 
any icy rock and dust kicked up by the impact of the 354-
pound spacecraft.

     "There are several possible explanations why we did 
not detect any water signature, and none of them can 
really be discounted at this time," said Dr. Ed Barker, 
assistant director of the university's McDonald 
Observatory at UT Austin, who coordinated the observing 
campaign.  These explanations include:

*  the spacecraft might have missed the target area;
*  the spacecraft might have hit a rock or dry soil at 
   the target site;
*  water molecules may have been firmly bound in rocks as 
   hydrated mineral as opposed to existing as free ice 
   crystals, and the crash lacked enough energy to separate 
   water from hydrated minerals;
*  no water exists in the crater and the hydrogen 
   detected by the Lunar Prospector spacecraft earlier is 
   simply pure hydrogen;
*  studies of the impact's physical outcome were 
   inadequate;
*  the parameters used to model the plume that resulted 
   from the impact were inappropriate;
*  the telescopes used to observe the crash, which have a 
   very small field of view, may not have been pointed 
   correctly;
*  water and other materials may not have risen above the 
   crater wall or otherwise were directed away from the 
   telescopes' view.

     Although the crash did not confirm the existence of 
water ice on the Moon, "this high-risk, potentially high-
payoff experiment did produce several benefits," said Dr. 
David Goldstein, the aerospace engineer who led the UT 
Austin team.  "We now have experience building a 
remarkably complex, coordinated observing program with 
astronomers across the world, we established useful upper 
limits on the properties of the Moon's natural 
atmosphere, and we tested a possible means of true 'lunar 
prospecting' using direct impacts."

     Lunar Prospector was launched on Jan. 6, 1998, from 
Cape Canaveral Air Station, FL, aboard an Athena 2 
rocket.  In March 1998, mission scientists announced 
their first tentative findings of the presence of water 
ice in shadowed craters near the Moon's south and north 
poles.  They estimated later that up to six billion 
metric tons of water ice may be buried in these craters 
under about 18 inches of soil, in more concentrated 
deposits than originally thought.  However, the evidence 
was indirect, they cautioned, based on reasonable 
scientific assumptions given the levels of hydrogen 
detected, from which water ice is inferred.

     Since then, Prospector data have also been used to 
develop the first precise gravity map of the entire lunar 
surface.  While the Moon's magnetic field is relatively 
weak, Prospector has confirmed the presence of local 
magnetic fields that create the two smallest 
magnetospheres in the Solar System.  Another scientific 
landmark is the assembly of the first global maps of the 
Moon's elemental composition.

     The $63 million Lunar Prospector mission was led by 
Dr. Alan Binder of the Lunar Research Institute, Tucson, 
AZ, and managed by NASA's Ames Research Center in Moffett 
Field, CA.  It was built by Lockheed Martin Missiles & 
Space, Sunnyvale, CA.  Other participating organizations 
included the Department of Energy's Los Alamos National 
Laboratory, NM, and NASA's Goddard Space Flight Center, 
Greenbelt, MD, and Jet Propulsion Laboratory, Pasadena, 
CA.  

                             -end-

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