16 AUG B-M-B

Dark brown sample with clasts ranging from small to large in size. The clast shape ranges from angular to sub-rounded. Lineations can be commonly seen throughout the sample, along with comet structures. A few necking structures can also be observed. The most notable necking structure is between a few very large clasts. Minor amounts of grain crushing can be seen.

16 AUG B-I-A

Dark brown sediment with clasts ranging from small to large. Clast shape ranges from angular to sub-rounded. Rotation structures and comet structures can be commonly seen throughout the sample. Lineations along with minor amounts of grain crushing can also be seen in this sample.

A-3-B

Dark grey sediment with clasts ranging from small to large. Clast shape ranges from angular to sub-rounded in shape. Lineations are abundant in this sample. Comet structures can also be seen . There are minor amounts of rotation structures in this sample, and some clasts have faint rotation structures surrounding them. Minor amounts of grain crushing can also be seen.

RRC-1

Brown sediment with clasts ranging from small to large in size. Clast shape ranges from angular to sub-rounded. Lineations and rotation structures can be commonly seen throughout the sample. Minor amounts of comet structures, grain crushing and grain stacking can also be seen.

1493 BH17 NP 2014

Brown sediment with clasts ranging from small to large. Clast shape ranges from angular to rounded. Lineations and comet structures are abundant throughout this sample. It also contains rotation structures and minor amounts of grain crushing.

1501 BH17 NP 2014

Brown sediment with clasts ranging from small to large in size. Clast shape ranges from angular to sub-rounded. Lineations and comet structures are commonly seen throughout the sample. Rotation structures with and without central grains can also be seen.

1507 BH17 NP 2014

Brown sediment with clasts ranging from small to large in size. Clast shape ranges from angular to rounded. Lineations and rotation structures were abundant in this sample, Rotation structures were seen with and without central grains. Comet structures were also present in this sample along with minor amounts of grain stacking.

1520 BH17 NP 2014

Dark brown sediment with clasts ranging from small to large in size. Clast shape ranges from angular to sub-rounded. Lineations can be seen throughout the sample, along with a few rotation and comet structures. This sample also contains a fine grained clay domain that is relatively structure-less. It can be seen scattered throughout the sample.

1523 BH17 NP 2014

Brown sediment with clasts ranging from small to large in size. Clast shape ranges from angular to sub-rounded. Lineations and rotation structures are abundant throughout the sample. Comet structures can also be seen. Minor amounts of grains crushing/stacking are also present.

1526 BH17 NP 2014

Brown sediment with clasts ranging from small to medium in size. Clast shape ranges from angular to sub-rounded. Rotation structures and comet structures are commonly seen throughout this sample. Lineations are also common. Minor amounts of grain stacking can also be seen. Some grains appear to be fractured and/or weathered.

1539 BH17 NP 2014

Brown sediment with clasts ranging from small to large. Clast shape ranges from angular to sub-rounded. Lineations are common throughout the sample. This sample also contains a clay domain, that appears very fine grained. Edge-to-edge grain crushing, comet structures, and rotation structures are also present.

1542 BH17 NP 2014

Brown sediment with clasts ranging from small to large. Clast shape ranges from angular to sub-rounded. Lineations and rotation structures are scattered throughout the entire sample. Comet structures are also present. Minor amounts of grain stacking can also be seen.

1544 BH17 NP 2014

Brown sediment with inclusions of a clay rich domain. Clasts range from small to medium in size and angular to sub-rounded in shape. Lineations can be commonly seen throughout the sample, along with water escape structures in the clay rich domain. Rotation structures, comet structures, and grain crushing are also present.

Gravitational slopes, geomorphology, and material strengths of the nucleus of comet 67P/Churyumov-Gerasimenko from OSIRIS observations

Aims. We study the link between gravitational slopes and the surface morphology on the nucleus of comet 67P/Churyumov-Gerasimenko and provide constraints on the mechanical properties of the cometary material (tensile, shear, and compressive strengths). Methods. We computed the gravitational slopes for five regions on the nucleus that are representative of the different morphologies observed on the surface (Imhotep, Ash, Seth, Hathor, and Agilkia), using two shape models computed from OSIRIS images by the stereo-photoclinometry (SPC) and stereo-photogrammetry (SPG) techniques. We estimated the tensile, shear, and compressive strengths using different surface morphologies (overhangs, collapsed structures, boulders, cliffs, and Philae's footprint) and mechanical considerations. Results. The different regions show a similar general pattern in terms of the relation between gravitational slopes and terrain morphology: i) low-slope terrains (0-20 degrees) are covered by a fine material and contain a few large (>10 m) and isolated boulders; ii) intermediate-slope terrains (20-45 degrees) are mainly fallen consolidated materials and debris fields, with numerous intermediate-size boulders from <1m to 10m for the majority of them; and iii) high-slope terrains (45-90 degrees) are cliffs that expose a consolidated material and do not show boulders or fine materials. The best range for the tensile strength of overhangs is 3-15 Pa (upper limit of 150 Pa), 4-30 Pa for the shear strength of fine surface materials and boulders, and 30-150 Pa for the compressive strength of overhangs (upper limit of 1500 Pa). The strength-to-gravity ratio is similar for 67P and weak rocks on Earth. As a result of the low compressive strength, the interior of the nucleus may have been compressed sufficiently to initiate diagenesis, which could have contributed to the formation of layers. Our value for the tensile strength is comparable to that of dust aggregates formed by gravitational instability and tends to favor a formation of comets by the accrection of pebbles at low velocities.

Morphology and dynamics of the jets of comet 67P/Churyumov-Gerasimenko: Early-phase development

Aims. The OSIRIS camera onboard the Rosetta spacecraft obtained close-up views of the dust coma of comet 67P. The jet structures can be used to trace their source regions and to examine the possible effect of gas-surface interaction. Methods. We analyzed the wide-angle images obtained in the special dust observation sequences between August and September 2014. The jet features detected in different images were compared to study their time variability. The locations of the potential source regions of some of the jets are identified by ray tracing. We used a ring-masking technique to calculate the brightness distribution of dust jets along the projected distance. Results. The jets detected between August and September 2014 mostly originated in the Hapi region. Morphological changes appeared over a timescale of several days in September. The brightness slope of the dust jets is much steeper than the background coma. This might be related to the sublimation or fragmentation of the emitted dust grains. Interaction of the expanding gas flow with the cliff walls on both sides of Hapi could lead to erosion and material down-fall to the nucleus surface.