NASA's LRO Exposes Moon's Complex, Turbulent Youth

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Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui.c.cook@jpl.nasa.gov

Nancy Neal Jones/Bill Steigerwald 301-286-0039/5071
Goddard Space Flight Center, Greenbelt, Md.
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NEWS RELEASE: 2010-303 Sept. 16, 2010

NASA'S LRO EXPOSES MOON'S COMPLEX, TURBULENT YOUTH

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-303&cid=release_2010-303

PASADENA, Calif. – The moon's surface is more complex than previously thought and was
bombarded by two distinct populations of asteroids or comets in its youth, according to three new
papers in the Sept. 17 issue of Science that describe data from NASA's Lunar Reconnaissance
Orbiter.

Two of the papers describe data from LRO's Diviner Lunar Radiometer Experiment instrument that
reveal the complex geologic processes that forged the lunar surface. The data showed previously
unseen compositional differences in the crustal highlands, and confirmed the presence of anomalously
silica-rich material in five distinct regions.

All minerals and rocks absorb and emit energy with unique signatures that reveal their identity and
formation mechanisms. For the first time, the Diviner instrument is providing scientists with global,
high-resolution infrared maps of the moon, enabling them to make a definitive identification of
silicate minerals commonly found within its crust. "Diviner is literally viewing the moon in a whole
new light," said Benjamin Greenhagen of NASA's Jet Propulsion Laboratory in Pasadena, Calif., lead
author of one of the Diviner papers.

Lunar geology can be roughly broken down into two categories – the anorthositic highlands, rich in
calcium and aluminium, and the basaltic "maria," giant impact basins filled with solidified lava flows
that are abundant in iron and magnesium. Both of these crustal rocks are considered the direct result
of crystallization from lunar mantle material, the partially molten layer beneath the crust.

Diviner's observations have confirmed that most lunar terrains have signatures consistent with
compositions in these two broad categories. But they have also revealed lunar soil compositions with
more sodium than that of typical anorthosite crust. The widespread nature of these soils reveals that
there may have been variations in the chemistry and cooling rate of the magma ocean that formed the
early lunar crust, or they could be the result of secondary processing of the early lunar crust.

Most impressively, in several locations around the moon, Diviner has detected highly silicic minerals
such as quartz, potassium-rich and sodium-rich feldspar -- minerals that are only associated with
highly evolved lithologies, or rocks that have undergone extensive magmatic processing. Detection of
silicic minerals at these locations is significant, as they occur in areas previously shown to exhibit
anomalously high abundances of the element thorium, another proxy for highly evolved lithologies.

"The silicic features we've found on the moon are fundamentally different from the more typical
basaltic mare and anorthositic highlands," said Timothy Glotch of Stony Brook University, N.Y., lead
author of the second Diviner paper. "The fact that we see this composition in multiple geologic
settings suggests that there may have been multiple processes producing these rocks."

One thing not apparent in the data is evidence for pristine lunar mantle material, which previous
studies have suggested may be exposed at some places on the lunar surface. Even in the South Pole
Aitken basin, also known as SPA, the largest, oldest, and deepest impact crater on the moon -- deep
enough to have penetrated through the crust and into the mantle -- there is no evidence of mantle
material.

The implications of this are as yet unknown. Perhaps there are no such exposures of mantle material,
or maybe they occur in areas too small for Diviner to detect. But it's likely that if the impact that
formed this crater did excavate any mantle material, it has since been mixed with crustal material from
later impacts inside and outside the basin.

"The new Diviner data will help in selecting the appropriate landing sites for potential future robotic
missions to return samples from SPA," Greenhagen said. "We want to use these samples to date the
SPA-forming impact and potentially study the lunar mantle, so it's important to use Diviner data to
identify areas with minimal mixing."

In the other paper, lead author James Head of Brown University in Providence, R.I., describes an
analysis of a detailed global topographic map of the moon created using LRO's Lunar Orbiter Laser
Altimeter. This new dataset shows that the older highland impactor population can be clearly
distinguished from the younger population in the lunar maria. The highlands have a greater density of
large craters, implying that the earlier population of impactors had a proportionally greater number of
large fragments than the population characterizing later lunar history, Head said.

Head said details about impactor populations on the moon have implications for the earliest history of
all the planets in the inner solar system, including Earth. "Like the Rosetta stone, the lunar record can
be used to translate the 'hieroglyphics' of the poorly preserved impact record on Earth," he said.

NASA's Goddard Space Flight Center in Greenbelt, Md., built and manages the Lunar
Reconnaissance Orbiter, a NASA mission with international participation from the Institute for Space
Research in Moscow. JPL designed, built and operates the Diviner instrument. The University of
California, Los Angeles is the home institution of Diviner's principal investigator, David Paige.
LOLA was built by Goddard.

A more detailed release on the LRO results is available at http://www.nasa.gov/lro . More information
is also available on the Diviner website at http://diviner.ucla.edu .

-end-

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