SMART-1 DIAGNOSES WRINKLES AND EXCESS WEIGHT IN HUMORUM AND PROCELLARUM BASINS

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Owing to SMART-1’s high resolution and the favourable illumination conditions during the satellite’s scientific operations, data from Europe’s lunar orbiter is helping put together a story linking geological and volcanic activity on the Moon. The combination of high resolution data from SMART-1’s AMIE micro-camera and data from the US Clementine mission is helping scientists determine the tectonics of the Moon’s giant basins and the history of volcanic flooding of mid-sized craters, inside and around the lunar basins.

“Thanks to low-elevation solar illumination on these high resolution images”, says SMART-1 Project Scientist Bernard Foing, “it is now possible to study fine, small scale geological features that went undetected earlier.”

The study provides new information on the thermal and tectonic history of the Moon and the processes following the formation of the large basins.

There are approximately 50 recognizable lunar basins more than 300 km in diameter. They are believed to be created by the impact of asteroids or comets during the Lunar Late Heavy Bombardment period, 350-750 million years after the formation of the Moon. Some of these basins (mostly on the near side) were then filled in by lava originating from volcanic activity.

Combining information from SMART-1 and Clementine makes it possible to assess the link between fine geological structures, identified for the first time with AMIE’s high resolution, and the chemical composition of the study area.

The Humorum basin is an ‘ideal’, circular, compact and moderately thick basin that was created by a simple impact event, showing a thin crust and mass concentration within a small area (from Clementine topography and gravity data).

The Procellarum basin, or Oceanus Procellarum, is a large, extended, complex basin that is moderately thick and shows no mass concentration. It may have been formed by faulting associated with the formation of the adjacent Imbrium crater (3.84 thousand million years ago), rather than by a ‘gargantuan’ impact.

The Humorum basin shows concentric graben, or elongated, trench-like erosional features around the edge of the basin. These are formed as the crust is deformed due to the presence of a mascon (mass concentration or ‘local overweight’).

“Lunar crust is like a fragile skin, wrinkled due to local mascons or its thermal history”, says Bernard Foing, “as doctors, we searched for these skin-imprints but some may be masked underneath the latest basalt layers”

For the first time, strike-slip faults have been observed with SMART-1 in the Humorum basin. These are faults where the rupture is vertical and one side slides past the other. An example is the San Andreas fault along the western United States, however there is no multi-plate tectonic activity on the Moon.

Procellarum is an extended basin, where magma has arisen from under the surface, 4 to 2 thousand million years ago, as the crust is thin enough.

SMART-1 images do not show geological faults, or surfaces where the rock ruptures due to differential movement, in the Procellarum basin.

It however shows wrinkle ridges that are not distributed radially around the basin. Due to their location, they do not seem associated with mascon tectonics, but mostly are results of thermal and mechanical deformation resulting from volcanic activity – basalt extruded by the lava causes compression in the area. The Procellarum basin contains the youngest basalt found on the Moon so far, up to 2 thousand million years old.

Different ‘pulses’ of volcanic activity in lunar history created units of lava on the surface. The flooding of mid-sized craters with lava due to volcanic activity in the region is reflected in the mineralogical map.

Differences in the mineralogical composition provide a tool to study the geological history of the region. Flooded as well as unflooded craters are found in the region, reflecting the evolution of volcanic activity with time.

“This analysis shows the potential of the AMIE camera”, says Jean-Luc Josset, Principal Investigator for the AMIE camera, “and we are still analysing other datasets that make use of the varying illumination conditions during the operation of SMART-1 over one and half years”.

Notes for editors: The results reflected in the article appear in ‘Coupling between impacts and lunar volcanism for Humorum and Procellarum basins’ by S. Peters, B. Foing, D. Koschny, A. Rossi and SMART-1 AMIE team, presented at the European Planetary Science Congress on 22 August 2007.
Stefan Peters performed this work while he was a trainee at the Research and Scientific Support Department at ESA’s European Space Research and Technology Centre.

Images

Credit for all images: ESA/SMART-1 and SPACE-X, Space Exploration Institute

1. Short caption: Mare Humorum
Long caption: This is a SMART-1 AMIE image mosaic of the edge of Mare Humorum. It shows basalt deposits to the right and graben, or elongated, trench-like erosional fault structures, around the basin. The images were taken from a distance of 1070 km, centred at 46° West and 27° South. The overall image field measures 200 x 130 km.

2. Short caption: Mare Humorum and Oceanus Procellarum
Long Caption: The positions of Mare Humorum (H) and Oceanus Procellarum (P) basins are indicated on a Mercator map of the Moon centred on the near-side.

3. Short caption: Mare Humorum
Long caption: This is an image mosaic of pictures taken by SMART-1’s AMIE camera. It shows a part of the Humorum basin showing graben features or elongated, trench-like erosional features. The size of individual images is 50 km.

4. Short caption: Mare Humorum
Long caption: This is a SMART-1 AMIE image of a part of the Humorum basin showing strike slip faults and tectonic wrinkles due to crust deformation around a basin mascon (mass concentration or ‘local overweight’).

5. Short caption: Graben features and strike-slip faults in Mare Humorum
Long caption: This image shows graben features (red), strike slip faults (green) and wrinkle ridges (blue) as determined with SMART-1 AMIE in a context Clementine image of Humorum basin. Graben features are elongated, trench-like erosional structures which form as the crust is deformed due to the presence of a mascon (mass concentration or ‘local overweight’). Strike-slip faults are faults where the rupture is vertical and one side slides past the other. An example is the San Andreas fault along the western United States, however there is no multi-plate tectonic activity on the Moon. Wrinkle ridges in the Humorum basin are believed to be caused by thermo-mechanical deformation of the mare basalts, rather than mascon tectonics (due to mass concentration, or local ‘overweight’).

6. Short Caption: Wrinkle ridges in Mare Humorum
Long Caption: This SMART-1 AMIE image shows wrinkle ridges in the Humorum basin are indicated in blue. They are believed to be caused by thermo-mechanical deformation of the mare basalts, rather than mascon tectonics (due to mass concentration, or local ‘overweight’).

7. Short Caption: Wrinkle ridges in Oceanus Procellarum
Long Caption: Wrinkle ridges detected with SMART-1 in the Procellarum basin. It however shows wrinkle ridges that are not distributed radially around the basin. Due to their location, they do not seem associated with mass concentration tectonics, but mostly are results of thermal and mechanical deformations resulting from volcanic activity – due to compression from basalt extruded by the lava. The Procellarum basin contains the youngest basalt found on the Moon so far, up to 2 billion years old.

8. Short Caption: Hansteen and Billy
Long Caption: This picture shows the craters Hansteen (top) and Billy (bottom), both lying in the Procellarum basin. Billy is an example of a crater flooded due to volcanic activity, whereas Hansteen remains unflooded. The craters are 45 km in diameter.