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Bright Ray Craters on Ganymede Observed from Galileo and Voyager Images
| Content Provider | Semantic Scholar |
|---|---|
| Author | Miyamoto, H. Hirata, N. |
| Copyright Year | 2016 |
| Abstract | Introduction: Ray craters are recognized to be the youngest feature on Ganymede [1], and represents the most recent impact cratering [2]. Also, being susceptible to destruction by various processes [1-3], ray craters may inform on the most recent geologic processes on Ganymede. Passey and Shoemaker [4] identified 84 bright ray craters D>30 km and obtained several preliminary results and conclusions using the image data of Voyager. However, since Voyager 1 and 2 only have sufficient resolution (better than 2 km/pixel) images limiting to the subjovian and antijovian surroundings [4, 5], the analysis of Galileo images could fill in this gap. Also, the revised global geologic map [5] and advanced cratering impact model [2] make a more accurate distribution and a more comprehensive understanding of bright ray craters of Ganymede possible, which is the target of this study. Data and Methods: We used the global image mosaic compiled from Voyager and Galileo images with a global resolution of 1 km/pixel to measure the locations and diameters of the ray craters and the related areas. The map is available via USGS Astrogeology Science Center. Also, since the crater rays are sensitive to solar illumination [2], we used the raw images of both Voyager and Galileo images (825 Voyager images and 314 Galileo images) to identify ray craters at high sun as much as possible. These images are available via Planetary Data System of NASA. Considering the coverage and resolution of the raw images, we only measured the ray craters with D>10 km in the latitudinal range 70°N-70°S, and omitted the regions with resolution lower than 3 km/pixel [5]. Ultimately, our work resulted in a revised density distribution of bright ray craters corresponding to latitude, angular apex distance, and different terrain types. Results: We identified a total of 257 ray craters D>10 km on 92% of the surface of Ganymede, which includes 188 craters from Voyager images and 69 from Galileo images, among them 67 craters on Dark Terrain and 190 on Bright Terrain. Figure 1 shows the cumulative size frequency distribution (referred to hereafter as CSFD) of bright ray craters D>10 km on both Dark and Bright Terrain. It is obvious that for bright ray craters D<~100km, the density on Bright Terrain is systematically higher than that on Dark Terrain for ranging crater diameters, which is consistent with Passey and Shoemaker [4], suggesting that crater rays are either more difficult to be produced or easier to be erased on Dark Terrain. In addition, big ray craters (D>100km) are very few (only 7 in number) and randomly distributed, resulting in a different CSFD curve for ray craters D>~100 km. Figure 2 shows the distribution of bright ray craters D>10km as a function of the angular distance from the apex of motion. The density of bright ray craters on both Dark and Bright Terrain has a peak near apex distance of 80-110° (around prime meridian and anti-meridian). Also, bright ray craters on the Leading Hemisphere Figure 1. The cumulative size frequency distribution of bright ray craters on Dark Terrain and Bright Terrain, with density/√N error bars. |
| Starting Page | 2003 |
| Ending Page | 2003 |
| Page Count | 1 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://www.hou.usra.edu/meetings/lpsc2016/pdf/2003.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
