[meteorite-list] Lutetia's Dark Side Hosts Hidden Crater

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 8 Oct 2014 15:44:52 -0700 (PDT)
Message-ID: <201410082244.s98MiqUd021812_at_zagami.jpl.nasa.gov>

http://sci.esa.int/rosetta/54741-lutetias-dark-side-hosts-hidden-crater/

Lutetia's dark side hosts hidden crater
European Space Agency
08 October 2014

Grooves found on Lutetia, an asteroid encountered by ESA's
Rosetta spacecraft, point to the existence of a large impact
crater on the unseen side of the rocky world.

Rosetta flew past Lutetia at a distance of 3168 km in July 2010,
en route to its 2014 rendezvous with its target comet.

The spacecraft took images of the 100 km-wide asteroid for about
two hours during the flyby, revealing numerous impact craters and
hundreds of grooves all over the surface.

Impact craters are commonly seen on all Solar System worlds with
solid surfaces, recording an intense history of collisions between
bodies. However, grooves are much less prevalent. To date, they
have been discovered by visiting spacecraft only on the martian
moon Phobos and the asteroids Eros and Vesta.

The way in which grooves are formed on these bodies is still
widely debated, but it likely involves impacts. Shock waves from
the impact travel through the interior of a small, porous body and
fracture the surface to form the grooves.

"For Lutetia, by assuming that the grooves were formed in
concentric patterns around their source impact crater, we
identified 200 such features falling into distinct 'families',
correlated with three different impact craters," describes
Sebastien Besse, a research fellow at ESA's Technical Centre,
ESTEC, in the Netherlands, and lead author of the paper published
in Planetary and Space Science this month.

One of the groove systems on Lutetia is associated with the
Massilia crater and another with the North Pole Crater Cluster,
which comprises a number of superimposed craters. Both are on the
asteroid's northern hemisphere.

But another group of grooves points to a crater not seen during
Rosetta's brief flyby, in the asteroid's southern hemisphere.

Its implied presence has earned it the nickname 'Suspicio'. The
grooves related to Suspicio cover a large area on the asteroid,
suggesting it may span several tens of kilometres. By comparison,
Massilia, the largest known crater on Lutetia, is about 55 km
wide, and the largest of the polar cluster is about 34 km across.

"These three major impacts seriously deformed Lutetia's
surface," adds Sebastien. "As with grooves seen on other
asteroids that may also be associated with impact events, this
study provides new insights into the catastrophic history of these
small bodies."

By observing how subsequent small craters lie over the grooves on
Lutetia, the scientists determined the relative ages of the three
larger cratering events. Massilia is thought be the oldest of the
three craters and the polar cluster the youngest, with Suspicio
between.

The authors also looked at other, independent measurements of
Lutetia, including ground-based observations with the Infrared
Telescope Facility and space-based observations with ESA's
Herschel and NASA's Spitzer.

Shape models derived by Herschel and Spitzer before Rosetta's
flyby had already predicted a large depression at the location of
Suspicio. The Infrared Telescope Facility suggested different
compositions between the northern and southern hemisphere of the
asteroid. Sebastien and his colleagues propose that a large
impact, presumably the one forming Suspicio, excavated enough
material of a different composition to account for the observed
differences.

"Our study ties together several independent analyses of Lutetia
into one coherent story that is consistent with the presence of a
large impact crater on the far side of the asteroid," says
co-author Michael Kuppers, from ESA's Space Astronomy Centre in Spain.

"Four years on and we are delighted still to be learning from
just two hours' worth of data collected during the Lutetia
flyby," says Matt Taylor, ESA's Rosetta project scientist.
"Rosetta is now in its main mission phase at its comet, where we
are on the cusp of fantastic results. Rosetta is a true small
bodies mission, two asteroids and one comet in single trip."


Notes for Editors

"Lutetia's lineaments
<http://dx.doi.org/10.1016/j.pss.2014.07.007>" is published in
Planetary and Space Science, 15 October 2014.


For further information, please contact:

Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mobile: +31 61 594 3 954
Email: markus.bauer at esa.int

Sebastien Besse
ESA's European Space Research and Technology Centre (ESTEC)
Noordwijk, the Netherlands
Email: sbesse at cosmos.esa.int

Michael Kuppers
ESA's European Space Astronomy Centre
Villanueva de la Canada, Madrid, Spain
Email: michael.kueppers at sciops.esa.int

Matt Taylor
ESA Rosetta Project Scientist
ESA's European Space Research and Technology Centre (ESTEC)
Noordwijk, the Netherlands
Email: matthew.taylor at esa.int
Received on Wed 08 Oct 2014 06:44:52 PM PDT