[P-PS08] Mars and Mars system: results from a broad spectrum of Mars studies and aspects for future missions

[PPS08-P05] Re-impacts from the craters residing at the deepest location generating the blue units on Phobos

*Hiroshi Kikuchi¹ (1.Japan Aerospace Exploration Agency)

Keywords:Impact processes, Mars satellites, Cratering

Re-impact sites from the deepest crater on a body in space preserve much of original information. The surface of the Martian satellite Phobos is spectrally divided into red and blue units [1]. The former are globally distributed, while the blue units have been observed inside and outside the Stickney crater—the largest and deepest crater on Phobos. Outside the crater, the blue units are concentrated in the region from the south to the west (south-west blue units) and in the region east of the crater (east blue units). Several models can explain the east blue units [e.g., 2, 3]. However, the mode of formation of the south-west blue units is still unknown, despite its vast area. We propose that the combination of ejecta from Stickney and Limtoc (a crater located on the floor of Stickney) contributes to the formation of the blue units. We test the model using ballistic simulations incorporating an updated shape model with randomly generated ejecta velocities, different values of orbital radii to Mars, and various launching velocities to track the emplacements of the ejecta particles. The results show the distribution of global blue units are recreated when the combined re-impact sites of ejecta from Stickney and Limtoc have orbital radius (X_Ph) values of X_Ph > 3.34 R_M and X_Ph < 3.04 R_M, respectively. This suggests that the blue material is concentrated deep underneath the surface, and the age of Stickney crater may be sufficiently old to be estimated from the crater densities [4].


References
1. Murchie, S.L., et al., COLOR HETEROGENEITY OF THE SURFACE OF PHOBOS - RELATIONSHIPS TO GEOLOGIC FEATURES AND COMPARISON TO METEORITE ANALOGS. Journal of Geophysical Research-Solid Earth and Planets, 1991. 96(B4): p. 5925-5945.
2. Shingareva, T.V. and R.O. Kuzmin, Mass-wasting processes on the surface of Phobos. Solar System Research, 2001. 35(6): p. 431-443.
3. Thomas, P.C., Ejecta emplacement on the Martian satellites. Icarus, 1998. 131(1): p. 78-106.
4. Schmedemann, N., et al., The age of Phobos and its largest crater, Stickney. Planetary and Space Science, 2014. 102: p. 152-163.