[meteorite-list] GRAIL Mission Points to Origin of 'Ocean of Storms' on Earth's Moon

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 1 Oct 2014 16:57:53 -0700 (PDT)
Message-ID: <201410012357.s91Nvr9P016463_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2014-333

NASA Mission Points to Origin of 'Ocean of Storms' on Earth's Moon
Jet Propulsion Laboratory
October 01, 2014

Using data from NASA's Gravity Recovery and Interior Laboratory (GRAIL),
mission scientists have solved a lunar mystery almost as old as the moon
itself.

Early theories suggested the craggy outline of a region of the moon's
surface known as Oceanus Procellarum, or the Ocean of Storms, was caused
by an asteroid impact. If this theory had been correct, the basin it
formed would be the largest asteroid impact basin on the moon. However,
mission scientists studying GRAIL data believe they have found evidence
the craggy outline of this rectangular region -- roughly 1,600 miles
(2,600 kilometers) across -- is actually the result of the formation of
ancient rift valleys.

"The near side of the moon has been studied for centuries, and yet
continues to offer up surprises for scientists with the right tools,"
said Maria Zuber, principal investigator of NASA's GRAIL mission, from
the Massachusetts Institute of Technology, Cambridge. "We interpret the
gravity anomalies discovered by GRAIL as part of the lunar magma
plumbing system -- the conduits that fed lava to the surface during
ancient volcanic eruptions."

The surface of the moon's near side is dominated by a unique area called
the Procellarum region, characterized by low elevations, unique
composition and numerous ancient volcanic plains.

The rifts are buried beneath dark volcanic plains on the near side of
the moon and have been detected only in the gravity data provided by
GRAIL. The lava-flooded rift valleys are unlike anything found anywhere
else on the moon and may at one time have resembled rift zones on Earth,
Mars and Venus. The findings are published online in the journal Nature.

Another theory arising from recent data analysis suggests this region
formed as a result of churning deep in the interior of the moon that led
to a high concentration of heat-producing radioactive elements in the
crust and mantle of this region. Scientists studied the gradients in
gravity data from GRAIL, which revealed a rectangular shape in resulting
gravitational anomalies.

"The rectangular pattern of gravity anomalies was completely
unexpected," said Jeff Andrews-Hanna, a GRAIL co-investigator at the
Colorado School of Mines in Golden, and lead author of the paper. "Using
the gradients in the gravity data to reveal the rectangular pattern of
anomalies, we can now clearly and completely see structures that were
only hinted at by surface observations."

The rectangular pattern, with its angular corners and straight sides,
contradicts the theory that Procellarum is an ancient impact basin,
since such an impact would create a circular basin. Instead, the new
research suggests processes beneath the moon's surface dominated the
evolution of this region.

Over time, the region would cool and contract, pulling away from its
surroundings and creating fractures similar to the cracks that form in
mud as it dries out, but on a much larger scale.

The study also noted a surprising similarity between the rectangular
pattern of structures on the moon, and those surrounding the south polar
region of Saturn's icy moon Enceladus. Both patterns appear to be
related to volcanic and tectonic processes operating on their respective
worlds.

"Our gravity data are opening up a new chapter of lunar history, during
which the moon was a more dynamic place than suggested by the cratered
landscape that is visible to the naked eye," said Andrews-Hanna. "More
work is needed to understand the cause of this newfound pattern of
gravity anomalies, and the implications for the history of the moon."

Launched as GRAIL A and GRAIL B in September 2011, the probes, renamed
Ebb and Flow, operated in a nearly circular orbit near the poles of the
moon at an altitude of about 34 miles (55 kilometers) until their
mission ended in December 2012. The distance between the twin probes
changed slightly as they flew over areas of greater and lesser gravity
caused by visible features, such as mountains and craters, and by masses
hidden beneath the lunar surface.

The twin spacecraft flew in a nearly circular orbit until the end of the
mission on Dec. 17, 2012, when the probes intentionally were sent into
the moon's surface. NASA later named the impact site in honor of late
astronaut Sally K. Ride, who was America's first woman in space and a
member of the GRAIL mission team.

GRAIL's prime and extended science missions generated the
highest-resolution gravity field map of any celestial body. The map will
provide a better understanding of how Earth and other rocky planets in
the solar system formed and evolved.

The GRAIL mission was managed by NASA's Jet Propulsion Laboratory (JPL)
in Pasadena, California, for NASA's Science Mission Directorate in
Washington. The mission was part of the Discovery Program managed at
NASA's Marshall Space Flight Center in Huntsville, Alabama. GRAIL was
built by Lockheed Martin Space Systems in Denver.

For more information about GRAIL, visit:

http://www.nasa.gov/grail

DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-9011
agle at jpl.nasa.gov

Dwayne Brown
NASA Headquarters, Washington
202-358-1726
dwayne.c.brown at nasa.gov

Kathleen Morton
Colorado School of Mines, Golden
303-273-3088
kmorton at mines.edu

2014-333
Received on Wed 01 Oct 2014 07:57:53 PM PDT