The global meter-level shape model of comet 67P/Churyumov-Gerasimenko

Context. From August 2014 to September 2016, the Rosetta spacecraft followed comet 67P/Churyumov–Gerasimenko along its orbit. After the comet passed perihelion, Rosetta performed a flyby manoeuvre over the Imhotep–Khepry transition in April 2016. The OSIRIS/Narrow-Angle-Camera (NAC) acquired 112 observations with mainly three broadband filters (centered at 480, 649, and 743 nm) at a resolution of up to 0.53 m/px and for phase angles between 0.095° and 62°. Aims. We have investigated the morphological and spectrophotometrical properties of this area using the OSIRIS/NAC high-resolution observations. Methods. We assembled the observations into coregistered color cubes. Using a 3D shape model, we produced the illumination conditions and georeference for each observation. We mapped the observations of the transition to investigate its geomorphology. Observations were photometrically corrected using the Lommel–Seeliger disk law. Spectrophotometric analyses were performed on the coregistered color cubes. These data were used to estimate the local phase reddening. Results. The Imhotep–Khepry transition hosts numerous and varied types of terrains and features. We observe an association between a feature’s nature, its reflectance, and its spectral slopes. Fine material deposits exhibit an average reflectance and spectral slope, while terrains with diamictons, consolidated material, degraded outcrops, or features such as somber boulders present a lower-than-average reflectance and higher-than-average spectral slope. Bright surfaces present here a spectral behavior consistent with terrains enriched in water-ice. We find a phase-reddening slope of 0.064 ± 0.001%/100 nm/° at 2.7 au outbound, similar to the one obtained at 2.3 au inbound during the February 2015 flyby. Conclusions. Identified as the source region of multiple jets and a host of water-ice material, the Imhotep–Khepry transition appeared in April 2016, close to the frost line, to further harbor several potential locations with exposed water-ice material among its numerous different morphological terrain units.

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Tensile strength of 67P/Churyumov–Gerasimenko nucleus material from overhangs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732155 ◽

2018 ◽

Vol 611 ◽

pp. A33 ◽

Cited By ~ 17

Author(s):

N. Attree ◽

O. Groussin ◽

L. Jorda ◽

D. Nébouy ◽

N. Thomas ◽

...

Keyword(s):

Tensile Strength ◽

Dynamic Stress ◽

Small Body ◽

Shape Model ◽

Lower Limits ◽

Comet 67P ◽

Rubble Pile ◽

Cometary Activity

We directly measured twenty overhanging cliffs on the surface of comet 67P/Churyumov–Gerasimenko extracted from the latest shape model and estimated the minimum tensile strengths needed to support them against collapse under the comet’s gravity. We find extremely low strengths of around 1 Pa or less (1 to 5 Pa, when scaled to a metre length). The presence of eroded material at the base of most overhangs, as well as the observed collapse of two features andthe implied previous collapse of another, suggests that they are prone to failure and that the true material strengths are close to these lower limits (although we only consider static stresses and not dynamic stress from, for example, cometary activity). Thus, a tensile strength of a few pascals is a good approximation for the tensile strength of the 67P nucleus material, which is in agreement with previous work. We find no particular trends in overhang properties either with size over the ~10–100 m range studied here or location on the nucleus. There are no obvious differences, in terms of strength, height or evidence of collapse, between the populations of overhangs on the two cometary lobes, suggesting that 67P is relatively homogenous in terms of tensile strength. Low material strengths are supportive of cometary formation as a primordial rubble pile or by collisional fragmentation of a small body (tens of km).

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Human face shape classification method based on active shape model

Journal of Computer Applications ◽

10.3724/sp.j.1087.2009.02710 ◽

2009 ◽

Vol 29 (10) ◽

pp. 2710-2712 ◽

Cited By ~ 2

Author(s):

Li-qiang DU ◽

Peng JIA ◽

Zong-tan ZHOU ◽

De-wen HU

Keyword(s):

Classification Method ◽

Active Shape Model ◽

Shape Classification ◽

Human Face ◽

Shape Model ◽

Face Shape ◽

Active Shape

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Evaluation of a Statistical Shape Model for the Liver

2018 International Conference on Image and Vision Computing New Zealand (IVCNZ) ◽

10.1109/ivcnz.2018.8634741 ◽

2018 ◽

Author(s):

Zhihui Lu ◽

Akinobu Shimizu ◽

Harvey Ho

Keyword(s):

Statistical Shape Model ◽

Shape Model ◽

Statistical Shape

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Semiautomatic Segmentation of Vertebrae in Lateral X-rays Using a Conditional Shape Model

Academic Radiology ◽

10.1016/j.acra.2007.06.003 ◽

2007 ◽

Vol 14 (10) ◽

pp. 1156-1165 ◽

Cited By ~ 16

Author(s):

J. Eugenio Iglesias ◽

Marleen de Bruijne

Keyword(s):

X Rays ◽

Shape Model ◽

Semiautomatic Segmentation

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Blocks Size Frequency Distribution in the Enceladus Tiger Stripes Area: Implications on Their Formative Processes

Universe ◽

10.3390/universe7040082 ◽

2021 ◽

Vol 7 (4) ◽

pp. 82

Author(s):

Maurizio Pajola ◽

Alice Lucchetti ◽

Lara Senter ◽

Gabriele Cremonese

Keyword(s):

Frequency Distribution ◽

Power Law ◽

Size Frequency Distribution ◽

Surface Stresses ◽

Size Frequency ◽

The One ◽

Power Law Index ◽

Comet 67P ◽

South Polar ◽

Degree Of Fragmentation

We study the size frequency distribution of the blocks located in the deeply fractured, geologically active Enceladus South Polar Terrain with the aim to suggest their formative mechanisms. Through the Cassini ISS images, we identify ~17,000 blocks with sizes ranging from ~25 m to 366 m, and located at different distances from the Damascus, Baghdad and Cairo Sulci. On all counts and for both Damascus and Baghdad cases, the power-law fitting curve has an index that is similar to the one obtained on the deeply fractured, actively sublimating Hathor cliff on comet 67P/Churyumov-Gerasimenko, where several non-dislodged blocks are observed. This suggests that as for 67P, sublimation and surface stresses favor similar fractures development in the Enceladus icy matrix, hence resulting in comparable block disaggregation. A steeper power-law index for Cairo counts may suggest a higher degree of fragmentation, which could be the result of localized, stronger tectonic disruption of lithospheric ice. Eventually, we show that the smallest blocks identified are located from tens of m to 20–25 km from the Sulci fissures, while the largest blocks are found closer to the tiger stripes. This result supports the ejection hypothesis mechanism as the possible source of blocks.

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Geometric correction for thermographic images of asteroid 162173 Ryugu by TIR (thermal infrared imager) onboard Hayabusa2

Earth Planets and Space ◽

10.1186/s40623-021-01437-w ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Takehiko Arai ◽

Tatsuaki Okada ◽

Satoshi Tanaka ◽

Tetsuya Fukuhara ◽

Hirohide Demura ◽

...

Keyword(s):

Surface Roughness ◽

High Surface ◽

Thermal Inertia ◽

Thermal Infrared ◽

Shape Model ◽

Infrared Imager ◽

Least Squares Fit ◽

Temperature Maps ◽

Pixel Scale ◽

Thermal Infrared Imager

AbstractThe thermal infrared imager (TIR) onboard the Hayabusa2 spacecraft performed thermographic observations of the asteroid 162173 Ryugu (1999 JU$$_3$$ 3 ) from June 2018 to November 2019. Our previous reports revealed that the surface of Ryugu was globally filled with porous materials and had high surface roughness. These results were derived from making the observed temperature maps of TIR using a projection method onto the shape model of Ryugu as geometric corrections. The pointing directions of TIR were calculated using an interpolation of data from the SPICE kernels (NASA/NAIF) during the periods when the optical navigation camera (ONC) and the light detection and ranging (LIDAR) observations were performed. However, the mapping accuracy of the observed TIR images was degraded when the ONC and LIDAR were not performed with TIR. Also, the orbital and attitudinal fluctuations of Hayabusa2 increased the error of the temperature maps. In this paper, to solve the temperature image mapping problems, we improved the correction method by fitting all of the observed TIR images with the surface coordinate addressed on the high-definition shape model of Ryugu (SFM 800k v20180804). This correction adjusted the pointing direction of TIR by rotating the TIR frame relative to the Hayabusa2 frame using a least squares fit. As a result, the temperature maps spatially spreading areas were converged within high-resolved $$0.5^\circ$$ 0 . 5 ∘ by $$0.5^\circ$$ 0 . 5 ∘ maps. The estimated thermal inertia, for instance, was approximately 300$$\sim$$ ∼ 350 Jm$$^{-2}$$ - 2 s$$^{-0.5}$$ - 0.5 K$$^{-1}$$ - 1 at the hot area of the Ejima Saxum. This estimation was succeeded in case that the surface topographic features were larger than the pixel scale of TIR. However, the thermal inertia estimation of smooth terrains, such as the Urashima crater, was difficult because of surface roughness effects, where roughness was probably much smaller than the pixel scale of TIR.

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