March 11, 2008
SMART-1 Captures New Lunar South Pole Images
Newly-released images of the lunar south-polar region obtained by ESA's SMART-1 are proving to be wonderful tools to zero-in on suitable study sites for potential future lunar exploration missions.
SMART-1's Advanced Moon Imaging Experiment (AMIE) has collected many images of the lunar south-polar region, with unprecedented spatial resolution. The images, obtained over a full year of changing seasons were used to study the different levels of solar illumination on the Moon's surface.
The orientation of the lunar rotation axis is such that the Sun just about grazes the lunar poles, leaving some regions permanently shadowed.
Shackleton crater is located in the inner ring of the south pole Aitken basin, the largest known impact basin in the solar system. It has a diameter of 2600 km.
The south pole is located on the rim of Shackleton crater. SMART-1 took images around the crater, which is a strong contender for a future robotic and human exploration site and for a permanent human base.
The polar mosaics show geological features of interest within reach from the south pole. Monitoring of the illumination of selected polar sites has allowed scientists to confirm that a ridge located 10 km from the Shackleton rim is prominently illuminated, and could be a strong contender for a potential future lunar outpost.
The large number of impact craters in the area indicates that the terrain is ancient. An example is crater Amundsen, 105 km in diameter, lying 100 km from the pole. It shows central peaks and asymmetric terraces that deserve geological and geochemistry studies.
The Lunar Prospector mission had previously indicated evidence of enhanced hydrogen in the permanent shadowed floors of polar craters, possible sign of water ice "“ a relevant element when choosing a human outpost.
As to whether or not ice could still be trapped under the floor of polar craters, the former SMART-1 Project Scientist Bernard Foing said, "To understand whether or not water is possibly present at the south pole, we have to take into account the following factors: how volatile elements were delivered to the lunar surface by comets or water-rich asteroids, whether they were destroyed or persisted under a dust cover and for how long they were able to accumulate."
"The polar regions are still lunar incognita, and it is critical to explore them and study their geological history," he added.
Using SMART-1 images, SMART-1 AMIE investigators and US collaborators have also counted small impact craters on Shackleton ejecta blanket to estimate the age of the crater. They have found that the number of craters is twice that of Apollo 15 landing site, which would make the Shackleton crater between 3.9 to 4.3 thousand million years old.
"Previous investigators believed Shackleton to be much younger, but that could be due to grazing illumination at the poles, which enhances the topography, mimicking a younger crater."
So, in view of SMART-1 observations, the south polar site looks even more interesting with the confirmation of prominently-lit sites, and the indication of old craters where ice could have had more time to accumulate in permanently-shadowed areas.
"The SMART-1 south polar maps indicate very exciting targets for science and future exploration, within travel reach from a rover or humans at the south pole", says Jean-Luc Josset, Principal Investigator for the AMIE.
These high-resolution SMART-1 south polar mosaics were produced and analyzed in the framework of a study project for the design and operations of lunar polar robotic landers and rovers, by Marina Ellouzi, a Master's student in space engineering at the Paris-Meudon Observatory. The south polar mosaics, SMART-1 highlights, and results on the geology and illumination of Shackleton crater are being presented and discussed by the SMART-1 AMIE team and collaborators at the 39th Lunar and Planetary Science Conference at League City, Texas between 11-12 March 2008.
Photo 1 Caption: This mosaic of the lunar south pole was obtained with images taken by the Advanced Moon Imaging Experiment (AMIE) on board ESA's SMART-1.
The pictures were taken between Dec 2005 and March 2006, during lunar southern summer. When obtaining the images, SMART-1 was flying over the south pole at a distance of about 500 km, allowing individual images with small-field (about 50 km across) high resolution views (50 m/pixel).
Each individual image includes areas imaged with colour filters and a more exposed area. The differences have been corrected accordingly to obtain this mosaic. The mosaic, composed of about 40 images obtained over more than 30 orbits, covers an area of about 500 by 150 km. The lunar near-side facing Earth is at the top of the map, while the far-side is at the bottom.
Credits: ESA/SMART-1/Space-X (Space Exploration Institute)
Photo 2 Caption: This mosaic of the lunar south pole was obtained with images taken by the Advanced Moon Imaging Experiment (AMIE) on board ESA's SMART-1. The pictures were taken between Dec 2005 and March 2006, during the lunar southern summer. The mosaic, composed of about 40 images, covers an area of about 500 by 150 km. The lunar near-side facing Earth is at the top of the map, while the far-side is at the bottom. A number of interesting lunar craters are indicated:
Shackleton, visible left-centre of the mosaic, is the crater which contains the lunar south pole within its rim. It is nearly circular (about 19 km across, centered at 89.9° south, 0.0° east), with a clear rim and a relatively flat crater floor marked by smaller craters inside. The southern part of its interior is permanently in shadow, making it difficult to image, but it is expected to be bowl-shape due to its modest size. It was named after the British polar explorer Ernest Shackleton.
Faustini, in the centre of the mosaic (87.3° south, 77.0° east), is a crater about 39 km across. The Lunar Prospector mission found that this crater has a higher-than-normal concentration of hydrogen. It was named after the Italian polar geographer explorer Arnaldo Faustini (1872-1944).
Shoemaker crater has been named after the geologist whose ashes were on board the Lunar Prospector spacecraft that impacted on the crater floor. 50 km in diameter, the crater is centred at 89.9° south, 0.0° east and is located between the Shackleton and Faustini craters. Lunar Prospector found that this crater has a higher-than-normal concentration of hydrogen. On July 1999, the mission crashed into the crater to create a plume of water vapor, but no detection was reported.
De Gerlache crater (diameter 32 km, centered at 88.5° south, 87.1° west) is located near Shackleton crater. Its floor is permanently shadowed. On the SMART-1 AMIE mosaic an illuminated saddle can be seen, bridging its rim to Shackleton. The crater is named after Adrien de Gerlache (1866, 1934), the Belgian antarctic explorer.
Amundsen is a large impact crater, about 105 km across, located along the southern lunar limb (84.5° south, 82.8° east), with its rim situated 110 km from the south pole. From Earth, this crater is viewed nearly from the side, illuminated by oblique sunlight. The crater rim is slightly distended along the southern edge, and the terraced surface is asymmetrical. Central peaks, that were formed from the rebound of the crust after the impact are quite apparent with their shadow projected over the flat floor.
Credits: ESA/SMART-1/Space-X (Space Exploration Institute)
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39th Lunar and Planetary Science Conference