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| Titel |
Properties of the Agilkia touchdown site on 67P from ROLIS high resolution imaging |
| VerfasserIn |
Stefano Mottola, Ralf Jaumann  , Stefan Schröder, Gabriele Arnold, Hans-Georg Grothues, Maximilian Hamm, Harald Michaelis, Ivanka Pelivan, Gerrit Proffe, Jean-Pierre Bibring |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110804
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| Publikation (Nr.) |
 EGU/EGU2015-10841.pdf |
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| Zusammenfassung |
| ROLIS (ROsetta Lander Imaging System) [1,2] is an imager with multispectral capabilities onboard the Rosetta Lander Philae. From its location on the instruments balcony and having a down-looking orientation, ROLIS acquired an imaging sequence of the Agilkia landing site during the descent onto comet 67P/Churyumov-Gerasimenko. These images provide the highest resolution available for the first touch-down site. The aim of the ROLIS experiment is to study the photometric properties, the morphology, the texture and microstructure of the comet's surface in order to understand the processes that control the cometary evolution.
ROLIS is a compact CCD imager with a 1k x 1k pixel sensor and a 57° field of view. During the descent it was focused to infinity and acquired panchromatic images. After landing ROLIS was refocused to a nominal distance of 30 cm and performed close-up, multi-spectral imaging of the soil, with help of a 4-color LED illumination device.
During the descent, ROLIS acquired images with a cadence of 10 s. Since the exact time of touchdown was not known, and due to storage and uplink capacity limitations, the images were stored in a ring buffer with the capacity of seven images, with the latest image overwriting the oldest. At the moment of touchdown the acquisition sequence was halted, and the last seven images −the ones with the highest resolution− were relayed to the orbiter. The landing occurred on Nov 12, 2014 at 15:34:04 UT. The sun elevation angle of about 30° provided near-ideal conditions for morphological analysis. The image acquired at the highest altitude (70 m) has a footprint of about 70 m and a resolution of 7 cm/pix, whereas the image closest to the surface was acquired at about 10 m altitude and has a resolution of about 1 cm/pix.
The high-resolution images acquired just before touchdown reveal a generally smooth and subdued terrain whose characteristics vary over scales of a few tens of meters. A comparatively uniform background made of particles below or at the resolution limit (about 1 cm on the image at closest range) is superimposed by debris and blocks ranging in size from centimeters to several meters with a regionally varying spatial density. Within the region imaged by ROLIS there appear to be undulated formations, terraces and pitted terrains. The spatial density of blocks varies with the type of terrain: the region with pits shows a significantly smaller presence of blocks than the neighboring regions. The appearance of the blocks themselves also varies considerably, ranging in shape from angular, polygonal to rounded. Some of the largest blocks resemble assemblages of smaller, similarly-sized units. The presence of clusters of block suggests that fragmentation and degradation processes are at work. Some blocks are partly buried by regolith, suggestive of dust mobilization.
References: [1] Mottola et al. (2007), SSR, 128, 241-255. [2] Michaelis et al. (1999), proc. SPIE 3794, 115-121. |
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