Characterization of the Abydos region through OSIRIS high-resolution images in support of CIVA measurements

Abstract

Context. On 12 November 2014, the European mission Rosetta delivered the Philae lander on the nucleus of comet 67P/ChuryumovGerasimenko (67P). After the first touchdown, the lander bounced three times before finally landing at a site named Abydos. Aims. We provide a morphologically detailed analysis of the Abydos landing site to support Philae's measurements and to give context for the interpretation of the images coming from the Comet Infrared and Visible Analyser (CIVA) camera system onboard the lander. Methods. We used images acquired by the OSIRIS Narrow Angle Camera (NAC) on 6 December 2014 to perform the analysis of the Abydos landing site, which provided the geomorphological map, the gravitational slope map, the size-frequency distribution of the boulders. We also computed the albedo and spectral reddening maps.Results. The morphological analysis of the region could suggest that Philae is located on a primordial terrain. The Abydos site is surrounded by two layered and fractured outcrops and presents a 0.02 km 2 talus deposit rich in boulders. The boulder size frequency distribution gives a cumulative power-law index of −4.0 + 0.3/−0.4, which is correlated with gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. The average value of the albedo is 5.8% at λ 1 = 480.7 nm and 7.4% at λ 2 = 649.2 nm, which is similar to the global albedos derived by OSIRIS and CIVA, respectively.

Close-up images of the final Philae landing site on comet 67P/Churyumov-Gerasimenko acquired by the ROLIS camera

“…The entire comet surface is probably active (e.g. Keller et al 2015), and Lucchetti et al (2016) confirm Abydos as a region where erosion takes place, presumably driven by activity. The ROLIS close-up images may therefore provide insight into the nature of cometary activity, the mechanics of which are still not well understood (Gundlach et al, 2015).…”

The Philae lander reveals low-strength primitive ice inside cometary boulders

“…Fly-bys and rendezvous missions have been central to the provision of close-up images of cometary surface structures, delivering important insights into the chemical and physical processes that have defined them 7 . The presence of boulders on their surfaces with sizes ranging from the metre scale up to tens of metres-often in locations not matching where they were initially exposed-certainly points to the dynamic nature of their creation 8,9 . A determination of mechanical strength properties derived from in situ measurements carried out on the primitive ice located in the interior of a cometary boulder allows unique comparisons to be made with the cometary body internal structure.…”

Multidisciplinary analysis of the Hapi region located on Comet 67P/Churyumov–Gerasimenko

“…Between 2014 August and October, the Rosetta spacecraft was placed at distances ranging from 100 to 25 km from the nucleus, resulting in an almost complete coverage of the northern and equatorial regions of 67P with a spatial resolution spanning 2 to 0.5 m. By means of this high-resolution image data set, different areas on 67P have been studied in great detail, such as the Maftet, Ma'at, Nut and Hatmehit areas (La Forgia et al 2015), the Abydos region (Lucchetti et al 2016), the circular niches in the Seth region (Lucchetti et al 2017), the Aswan site in the Seth region (Pajola et al 2016d) and the Imhotep region (Auger et al 2015). These analyses focused on localized areas of interest on 67P, expanding upon the geological maps presented in Giacomini et al (2016).…”