科研之友
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摘要
Context: Pinnacles, local promontories of varied shapes including spires with pointed tops, are observed on the surface of the 67P's cometary nucleus in the OSIRIS and NavCam images. Their presence and characteristics allow to infer the magnitude of the surface erosion and the degree of heterogeneity of the consolidated nucleus material. Aims: To identify these pinnacles and consider implications, which follow from their presence and characteristics. Methods: Identification of pinnacles in the available OSIRIS and NavCam images, as well as in the model images of the nucleus built from the digital terrain model, and an investigation of their morphology. Results: We identified and measured 49 pinnacles in 13 regions of the studied part of the nucleus. The pinnacles are typically asymmetric with somewhat different slope angles at different slopes whose maximum values range from 40 to 90 degrees, sometimes with small overhangs. Their heights vary from 10 to 20 to 100-200 m and the foot diameters from 30 to 300 m. Our analysis of the OSIRIS images of the pinnacles showed that they have surface texture similar to that of consolidated nucleus material and are probably composed of it. Conclusions: The observed characteristics of pinnacles found on 67P agree with the suggestion that they are erosion remnants formed due to a slowdown of erosion in places where nucleus material is more resistant to sublimational erosion than the material around it. In this case the maximum heights of pinnacles (100-200 m) gives a lower boundary for the amount of surface material lost and their diameters (typically tens of meters) are a measure of the size of the erosion-resistant parts.
- 出版日期2017-6
