ABSTRACT
The near-Earth asteroid (162173) Ryugu is thought to be a primitive carbonaceous object that contains hydrated minerals and organic molecules. We report sample collection from Ryugu's surface by the Hayabusa2 spacecraft on 21 February 2019. Touchdown images and global observations of surface colors are used to investigate the stratigraphy of the surface around the sample location and across Ryugu. Latitudinal color variations suggest the reddening of exposed surface material by solar heating and/or space weathering. Immediately after touchdown, Hayabusa2's thrusters disturbed dark, fine grains that originate from the redder materials. The stratigraphic relationship between identified craters and the redder material indicates that surface reddening occurred over a short period of time. We suggest that Ryugu previously experienced an orbital excursion near the Sun.
ABSTRACT
SUMMARY: Mandibular actinomycosis is an uncommon disease. We retrospectively reviewed 6 patients with pathologically proven mandibular actinomycosis who underwent both CT and MR imaging to evaluate the characteristic imaging findings. CT results showed an irregularly marginated lesion with increased bone marrow attenuation, osteolysis, and involvement of the skin in all patients. Periosteal reaction and intralesional gas were seen in 4 patients. MR imaging results revealed low signal on T1-weighted and high signal on T2-weighted images of the mandible, and moderate heterogeneous enhancement was seen in all patients who received intravenous contrast. Cervical lymphadenopathy was not observed. Involvement of the masseter, lateral pterygoid, and medial pterygoid muscles was seen in 4 patients, whereas parotid gland and submandibular gland as well as parapharyngeal space involvement were seen in 3 patients. Familiarity with the imaging findings of mandibular actinomycosis may help to diagnosis this entity.
