"Lunar Prospector has performed flawlessly over the past year," said Dr. Alan Binder, Lunar Prospector principal investigator and director of the Lunar Research Institute in Gilroy, Calif. "The quality of the data we've gathered is, in some cases, a factor of ten better than that which we promised to NASA at the outset, and we fulfilled all of our science objectives long before this first anniversary." "Lunar Prospector has been an extraordinarily successful mission," said Scott Hubbard, NASA Mission Manager at the Ames Research Center in Mountain View, Calif. "This little spacecraft has returned wonderful science and has proved the concept of 'faster, better, cheaper'."
On December 19, 1998, the spacecraft was commanded into a 40 kilometer (25 mile) lunar polar orbit, down from its 100 kilometer (63 mile) mapping orbit, signaling the transition to the extended mission. The spacecraft will remain in the new 40-km orbit for about 4 weeks, and then be commanded to an even closer 25 -30 km (approximately 15 to 19 mile) orbital path later this month. These actions will officially complete the end of the very successful primary mission, which began January 1998.
The extended mission is expected to continue through June 1999, during which time the five instruments onboard will gather additional science data at significantly higher resolutions. These higher resolutions will enable scientists to continue to refine their estimates concerning the concentration and form of hydrogen detected at the north and south lunar poles, which mission scientists interpret as deposits of water ice. Mapping of the Moon's magnetic and gravity fields will also benefit greatly from the lower orbit. Additionally, initial global maps of the Moon's elements will be confirmed with the close-up data.
Lunar Prospector was launched on Jan. 6, 1998, aboard a Lockheed Martin Athena 2 rocket and entered lunar orbit on Jan. 11, 1998. The Lunar Prospector mission is a joint effort of Lockheed Martin Missiles & Space, NASA Ames Research Center, and the Lunar Research Institute. Additional important contributions came from Los Alamos National Laboratory, the U.C. Berkeley Space Science Laboratory, and the NASA Goddard Space Flight Center. The $63 million mission is managed by the Ames Research Center.
Growing evidence now suggests that water ice deposits of relatively high concentration are trapped beneath the soil in the permanently shadowed craters of both lunar polar regions. The researchers believe that alternative explanations, such as concentrations of hydrogen from the solar wind, are unlikely.
In March of 1998, mission scientists reported a water signal with a minimum abundance of one percent by weight of water ice in rocky lunar soil (regolith) corresponding to an estimated total of 300 million metric tons of ice at the Moon's poles. "We based those earlier, conscientiously conservative estimates on graphs of neutron spectrometer data, which showed distinctive dips over the lunar polar regions," said Binder. "This indicated significant hydrogen enrichment, a telltale signature of the presence of water ice.
"Subsequent analysis, combined with improved lunar models, shows conclusively that there is hydrogen at the Moon's poles," Binder said. "Though other explanations are possible, we interpret the data to mean that significant quantities of water ice are located in permanently shadowed craters in both lunar polar regions.
"The data do not tell us definitively the form of the water ice," Binder added. "However, if the main source is cometary impacts, as most scientists believe, our expectation is that we have areas at both poles with layers of near-pure water ice." In fact, the new analysis "indicates the presence of discrete, confined, near-pure water ice deposits buried beneath as much as 18 inches (40 centimeters) of dry regolith, with the water signature being 15 percent stronger at the Moon's north pole than at the south."
How much water do scientists believe they have found? "It is difficult to develop a numerical estimate," said Dr. William Feldman, co-investigator and spectrometer specialist at the Department of Energy's Los Alamos National Laboratory, NM. "However, we calculate that each polar region may contain as much as three billion metric tons of water ice."
These mini-magnetospheres are located diametrically opposite to large impact basins on the lunar surface, leading scientists to conclude that the magnetic regions formed as the result of these titanic impacts. One theory is that these impacts produced a cloud of electrically charged gas that expanded around the Moon in about five minutes, compressing and amplifying the pre-existing, primitive ambient magnetic field on the opposite side. This field was then "frozen" into the surface crust and retained as the Moon's then-molten core solidified and the global field vanished
Lockheed Martin Missiles & Space, based in Sunnyvale, Calif., is a leading supplier of satellites and space systems to military, civil government and commercial communications organizations around the world. These spacecraft and systems have enhanced military and commercial communications; provided new and timely remote-sensing information; and furnished new data for thousands of scientists studying our planet and the universe.
January 6, 1999