Larry Klaes ( )
Tue, 16 Mar 1999 15:44:19 -0500

>Date: Tue, 16 Mar 1999 15:10:11 -0500 (EST)
>To: undisclosed-recipients:;
>Douglas Isbell
>Headquarters, Washington, DC March 16, 1999
>(Phone: 202/358-1547)
>David Morse
>Ames Research Center, Moffett Field, CA
>(Phone: 650/604-4724)
>RELEASE: 99-43
> Analysis of data from NASA's Lunar Prospector spacecraft has
>confirmed that the Moon has a small core, supporting the theory
>that the bulk of the Moon was ripped away from the early Earth
>when an object the size of Mars collided with the Earth.
> Scientists presented this result and other findings today in
>a series of papers at the 30th Lunar and Planetary Science
>Conference in Houston, TX. Their data show that the lunar core
>contains less than four percent of the Moon's total mass, with the
>probable value being two percent or slightly less. This is very
>small when compared with the Earth, whose iron core contains
>approximately 30 percent of the planet's mass.
> "This is a critical finding in helping scientists determine
>how the Earth and Moon formed," said Dr. Alan Binder of the Lunar
>Research Institute, Tucson, AZ, principal investigator for Lunar
> Similarities in the mineral composition of the Earth and the
>Moon indicate that they share a common origin. However, if they
>had simply formed form the same cloud of rocks and dust, the Moon
>would have a core similar in proportion to the Earth's. A third
>theory suggests that the moon was captured fully intact by the
>Earth's gravity.
> Based on information first gathered during the Apollo era,
>scientists suggested that the Moon was formed when a Mars-sized
>body hit the Earth during its earliest history. "This impact
>occurred after the Earth's iron core had formed, ejecting rocky,
>iron-poor material from the outer shell into orbit," Binder
>explained. "It was this material that collected to form the Moon.
> "Further analysis of Lunar Prospector data to refine the
>exact size of the lunar core and the amounts of elements like
>gold, platinum and iridium in lunar rocks -- all of which are
>concentrated with metallic iron -- is required," Binder added.
>"This will do much to pin down for good if the 'giant impact'
>model of the formation of the Moon is correct, or if the Moon
>formed in a different manner."
> The current data come from gravity measurements conducted by
>Dr. Alex Konopliv of NASA's Jet Propulsion Laboratory, Pasadena,
>CA. His results indicate that the Moon's core radius is between
>140 and 280 miles (220 and 450 kilometers). This result is
>consistent with independent magnetic data, evaluated by Dr. Lon
>Hood of the University of Arizona, Tucson, which suggest that the
>core radius is between 180 and 260 miles (300 and 425 km).
> In other results from Lunar Prospector, Dr. Robert Lin of the
>University of California at Berkeley, Dr. Mario Acuna of NASA's
>Goddard Space Flight Center, Greenbelt, MD, and Hood also found
>that a broad section of the southern far-side of the Moon has
>large localized magnetic fields in its crust. These fields occur
>opposite the large Crisium, Serenitatis and Imbrium basins --
>three of the "seas" that cover much of the Moon's near side. This
>result supports earlier evidence linking strong magnetized
>concentrations on one side of the Moon with young, large impact
>basins on the other side.
> Results of efforts to map the composition of the lunar crust
>have surpassed the expectations of the spectrometer team, led by
>Dr. William Feldman of the Department of Energy's Los Alamos
>National Laboratory in New Mexico. Data obtained are so good that
>the distribution of thorium has been mapped with a resolution of
>36 miles (60 kilometers). At this amount of detail, scientists
>can detect individual deposits rich in thorium and related
>elements. Their current observations suggest that thorium was
>excavated by impacts of asteroids and comets, and then distributed
>around craters, rather than being deposited by volcanic activity.
> Lunar Prospector conducted its primary mapping mission at an
>altitude of 63 miles (100 kilometers) for almost one year after
>its arrival in lunar orbit on Jan. 11, 1998. In December and
>January, the spacecraft's altitude was lowered to approximately 15
>miles by 23 miles (24 kilometers by 37 kilometers). Analyses of
>data from the lower-altitude observations are expected to further
>improve scientific understanding of the origin, evolution and
>physical resources of the Moon.
> The $63 million mission is managed by NASA's Ames Research
>Center, Moffett Field, CA, and was developed under NASA's
>Discovery Program of lower-cost, highly focused small scientific
> Further information about Lunar Prospector, its science data
>return, and relevant charts and graphics can be found on the
>project website at:
> -end-
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