[meteorite-list] SMART-1 Images: Gassendi Crater - Clue on the Thermal History of Mare Humorum

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Jul 6 15:25:23 2006
Message-ID: <200607061922.MAA21306_at_zagami.jpl.nasa.gov>

http://www.esa.int/SPECIALS/SMART-1/SEMV7DIO9PE_0.html

Gassendi crater - clue on the thermal history of Mare Humorum
SMART-1
European Space Agency
6 July 2006

This mosaic of two images, taken by the advanced Moon Imaging Experiment
(AMIE) on board ESA's SMART-1 spacecraft, shows the inside of crater
Gassendi on the Moon.
 
AMIE obtained these images on 13 January 2006, one minute apart from
each other, from a distance of about 1220 kilometres (top frame) and
1196 kilometres (bottom frame) from the surface, with a ground
resolution of 110 and 108 metres per pixel, respectively.

The area shown in the top image is centred at a latitude of 16.2? South
and longitude 40.2? West, while the bottom images is centred at a
latitude of 17.9? South and longitude 40.2? West.
 
Gassendi is an impact feature located on the near side of the Moon, at
the northern edge of Mare Humorum. The crater is actually much larger
than the field of view visible in this image. The hills on the lower
right of the mosaic are the central peak of the crater, with a height of
roughly 1.2 kilometres. The crater almost fully visible on the top is
called 'Gassendi A'.

Gassendi is a scientifically interesting site because it offers lunar
landers the possibility of sampling ancient highland rocks (in the
crater's central peak) as well as providing ages for both the Humorum
impact basin and the Gassendi crater itself. However, because the
terrain just outside the crater is quite rough, if a crew landed in this
region, it would be pretty difficult to reach Gassendi's central peaks
for sampling. Gassendi was considered as one of the three potential
sites for the Apollo 17 mission, that eventually touched ground in the
Taurus-Littrow valley.

The age of Gassendi crater is estimated to be about 3.6 thousand million
years (with an error of plus or minus 700 million years).

When observed through spectroscopic analysis, crater Gassendi presents a
'behaviour' very different from any other lunar crater (Mikhail 1979).
High resolution studies performed in the near-infrared light (Chevrel
and Pinet 1990, 1992) indicated the presence of extrusive volcanic
material (that is volcanic material flowing out from the surface and
then crystallising) limited to the southern portion of Gassendi's floor,
which is adjacent to Mare Humorum.

The interpretation of these data suggested that the central part of the
crater, including the peak complex, may have a more 'mafic' nature (that
is a composition of rocks coming from the solidification of magma which
are rich rich in iron and magnesium silicates, such as olivine and
pyroxene), with a higher pyroxene component than surrounding highlands.

The data interpretation also suggested that extensive extrusive
volcanism may have occurred within the eastern portion of the floor, as
also indicated by the significant presence of pyroxene that also
corresponds to visible volcanic features. The western part of the crater
floor, away from the geometric continuation of the western edge of Mare
Humorum, is composed of highlands-rich material.

The difference between the western and eastern side of the Gassendi
floor-fractured crater may be strongly linked to the early thermal
history of Mare Humorum.

The crater is named after Pierre Gassendi (1592-1655), French
philosopher, scientist and mathematician. In 1631, Gassendi became the
first person to observe the transit of a planet across the Sun, viewing
the transit of Mercury which Kepler had predicted.

 
For more information
 
Bernard H. Foing, ESA SMART-1 Project Scientist
Email: bernard.foing _at_ esa.int

Jean-Luc Josset, SPACE-X Space Exploration Institute
Email: jean-luc.josset _at_ space-x.ch

Patrick Pinet and Serge Chevrel, Observatoire Midi Pyrenees
Emails: patrick.pinet _at_ cnes.fr, chevrel @ dtp.obs-mip.fr
Received on Thu 06 Jul 2006 03:22:58 PM PDT