NASA Spacecraft Reveals Recent Geological Activity on the Moon
WASHINGTON -- New images from NASA's Lunar Reconnaissance Orbiter(LRO) spacecraft show the moon's crust is being stretched, forming
minute valleys in a few small areas on the lunar surface. Scientists
propose this geologic activity occurred less than 50 million years
ago, which is considered recent compared to the moon's age of more
than 4.5 billion years.
A team of researchers analyzing high-resolution images obtained by the
Lunar Reconnaissance Orbiter Camera (LROC) show small, narrow
trenches typically much longer than they are wide. This indicates the
lunar crust is being pulled apart at these locations. These linear
valleys, known as graben, form when the moon's crust stretches,
breaks and drops down along two bounding faults. A handful of these
graben systems have been found across the lunar surface.
"We think the moon is in a general state of global contraction because
of cooling of a still hot interior," said Thomas Watters of the
Center for Earth and Planetary Studies at the Smithsonian's National
Air and Space Museum in Washington, and lead author of a paper on
this research appearing in the March issue of the journal Nature
Geoscience. "The graben tell us forces acting to shrink the moon were
overcome in places by forces acting to pull it apart. This means the
contractional forces shrinking the moon cannot be large, or the small
graben might never form."
The weak contraction suggests that the moon, unlike the terrestrial
planets, did not completely melt in the very early stages of its
evolution. Rather, observations support an alternative view that only
the moon's exterior initially melted forming an ocean of molten rock.
In August 2010, the team used LROC images to identify physical signs
of contraction on the lunar surface, in the form of lobe-shaped
cliffs known as lobate scarps. The scarps are evidence the moon
shrank globally in the geologically recent past and might still be
shrinking today. The team saw these scarps widely distributed across
the moon and concluded it was shrinking as the interior slowly cooled.
Based on the size of the scarps, it is estimated that the distance
between the moon's center and its surface shrank by approximately 300
feet. The graben were an unexpected discovery and the images provide
contradictory evidence that the regions of the lunar crust are also
being pulled apart.
"This pulling apart tells us the moon is still active," said Richard
Vondrak, LRO Project Scientist at NASA's Goddard Space Flight Center
in Greenbelt, Md. "LRO gives us a detailed look at that process."
As the LRO mission progresses and coverage increases, scientists will
have a better picture of how common these young graben are and what
other types of tectonic features are nearby. The graben systems the
team finds may help scientists refine the state of stress in the lunar crust.
"It was a big surprise when I spotted graben in the far side
highlands," said co-author Mark Robinson of the School of Earth and
Space Exploration at Arizona State University, principal investigator
of LROC. "I immediately targeted the area for high-resolution stereo
images so we could create a three-dimensional view of the graben.
It's exciting when you discover something totally unexpected and only
about half the lunar surface has been imaged in high resolution.
There is much more of the moon to be explored."
The research was funded by the LRO mission, currently under NASA's
Science Mission Directorate at NASA Headquarters in Washington. LRO
is managed by NASA's Goddard Space Flight Center in Greenbelt, Md.
For more information about LRO and related images on the finding, visit:
http://www.nasa.gov/mission_
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