[FPSPACE] Fw: GSFC: NASA's LRO Reveals 'Incredible Shrinking Moon'
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Fri Aug 20 11:01:45 EDT 2010
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From: "AAS Press Officer Dr. Rick Fienberg" <rick.fienberg at aas.org>
Date: Fri, 20 Aug 2010 14:43:19
To: <Rick.Fienberg at aas.org>
Subject: GSFC: NASA's LRO Reveals 'Incredible Shrinking Moon'
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(FORWARDING DOES NOT IMPLY ENDORSEMENT BY THE AMERICAN ASTRONOMICAL
SOCIETY.) Rick Fienberg, AAS Press Officer: rick.fienberg at aas.org, +1
August 19, 2010
Bill Steigerwald / Nancy Neal-Jones
+1 301-286-5017 / +1 301-286-0039
william.a.steigerwald at nasa.gov / nancy.n.jones at nasa.gov
NASA'S LRO REVEALS 'INCREDIBLE SHRINKING MOON'
Newly discovered cliffs in the lunar crust indicate the Moon shrank
globally in the geologically recent past and might still be shrinking
today, according to a team analyzing new images from NASA's Lunar
Reconnaissance Orbiter (LRO) spacecraft. The results provide important
clues to the Moon's recent geologic and tectonic evolution.
The Moon formed in a chaotic environment of intense bombardment by
asteroids and meteors. These collisions, along with the decay of
radioactive elements, made the Moon hot. The Moon cooled off as it
aged, and scientists have long thought the Moon shrank over time as it
cooled, especially in its early history. The new research reveals
relatively recent tectonic activity connected to the long-lived
cooling and associated contraction of the lunar interior.
"We estimate these cliffs, called lobate scarps, formed less than a
billion years ago, and they could be as young as a hundred million
years," said Dr. Thomas Watters of the Center for Earth and Planetary
Studies at the Smithsonian's National Air and Space Museum,
Washington. While ancient in human terms, it is less than 25 percent
of the Moon's current age of more than four billion years. "Based on
the size of the scarps, we estimate the distance between the Moon's
center and its surface shrank by about 300 feet," said Watters, lead
author of a paper on this research appearing in Science August 20.
"These exciting results highlight the importance of global
observations for understanding global processes," said Dr. John
Keller, Deputy Project Scientist for LRO at NASA's Goddard Space
Flight Center, Greenbelt, Md. "As the LRO mission continues in to a
new phase, with emphasis on science measurements, our ability to
create inventories of lunar geologic features will be a powerful tool
for understanding the history of the Moon and the solar system."
The scarps are relatively small; the largest is about 300 feet high
and extends for several miles or so, but typical lengths are shorter
and heights are more in the tens of yards (meters) range. The team
believes they are among the freshest features on the Moon, in part
because they cut across small craters. Since the Moon is constantly
bombarded by meteors, features like small craters (those less than
about 1,200 feet across) are likely to be young because they are
quickly destroyed by other impacts and don't last long. So, if a small
crater has been disrupted by a scarp, the scarp formed after the
crater and is even younger. Even more compelling evidence is that
large craters, which are likely to be old, don't appear on top any of
the scarps, and the scarps look crisp and relatively undegraded.
Lobate scarps on the Moon were discovered during the Apollo missions
with analysis of pictures from the high-resolution Panoramic Camera
installed on Apollo 15, 16, and 17. However, these missions orbited
over regions near the lunar equator, and were only able to photograph
some 20 percent of the lunar surface, so researchers couldn't be sure
the scarps were not just the result of local activity around the
equator. The team found 14 previously undetected scarps in the LRO
images, seven of which are at high latitudes (more than 60 degrees).
This confirms that the scarps are a global phenomenon, making a
shrinking Moon the most likely explanation for their wide
distribution, according to the team.
As the Moon contracted, the mantle and surface crust were forced to
respond, forming thrust faults where a section of the crust cracks and
juts out over another. Many of the resulting cliffs, or scarps, have a
semi-circular or lobe-shaped appearance, giving rise to the term
"lobate scarps". Scientists aren't sure why they look this way;
perhaps it's the way the lunar soil (regolith) expresses thrust
faults, according to Watters.
Lobate scarps are found on other worlds in our solar system, including
Mercury, where they are much larger. "Lobate scarps on Mercury can be
over a mile high and run for hundreds of miles," said Watters. Massive
scarps like these lead scientists to believe that Mercury was
completely molten as it formed. If so, Mercury would be expected to
shrink more as it cooled, and thus form larger scarps, than a world
that may have been only partially molten with a relatively small core.
Our Moon has more than a third of the volume of Mercury, but since the
Moon's scarps are typically much smaller, the team believes the Moon
Because the scarps are so young, the Moon could have been cooling and
shrinking very recently, according to the team. Seismometers emplaced
by the Apollo missions have recorded moonquakes. While most can be
attributed to things like meteorite strikes, the Earth's gravitational
tides, and day/night temperature changes, it's remotely possible that
some moonquakes might be associated with ongoing scarp formation,
according to Watters. The team plans to compare photographs of scarps
by the Apollo Panoramic Cameras to new images from LRO to see if any
have changed over the decades, possibly indicating recent activity.
While Earth's tides are most likely not strong enough to create the
scarps, they could contribute to their appearance, perhaps influencing
their orientation, according to Watters. During the next few years,
the team hopes to use LRO's high-resolution Narrow Angle Cameras
(NACs) to build up a global, highly detailed map of the Moon. This
could identify additional scarps and allow the team to see if some
have a preferred orientation or other features that might be
associated with Earth's gravitational pull.
"The ultrahigh resolution images from the NACs are changing our view
of the Moon," said Dr. Mark Robinson of the School of Earth and Space
Exploration at Arizona State University, Tempe, Ariz., a coauthor and
Principal Investigator of the Lunar Reconnaissance Orbiter Camera.
"We've not only detected many previously unknown lunar scarps; we're
also seeing much greater detail on the scarps identified in the Apollo
# # #
Text & Images:
Briefing materials from Aug. 19 telecon:
The research was funded by NASA's Exploration Systems Mission
Directorate at NASA Headquarters, Washington. The team includes
researchers from the Smithsonian, Arizona State, the SETI Institute,
Mountain View, Calif., NASA Ames Research Center, Moffett Field,
Calif., Cornell University, Ithaca, N.Y., Institut fur Planetologie,
Westfalische Wilhelms-Universitat, Munster, Germany, Brown University,
Providence, R.I., and the Johns Hopkins University Applied Physics
Laboratory, Laurel, Md.
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