|
|||||
|
|
Crater clusters on Mars: Shedding light on martian ejecta launch conditions |
|
| Authors: | Olga P Popova William K Hartmann Derek C Richardson |
| Institution: | a Institute for Dynamics of Geospheres, Russian Academy of Sciences, Leninsky Prospekt 38, Bldg. 1, 119334 Moscow, Russia b Planetary Science Institute, 1700 East Fort Lowell Road, Suite 106, Tucson, AZ 85719-2395, USA c University of Maryland, Stadium Drive, College Park, MD 20742-2421, USA |
| Abstract: | We have identified two classes of crater clusters on Mars. One class is “small clusters” (crater diameter D∼ tens m, spread over few hundred m), fitting our earlier calculations for the breakup of weak stone meteoroids in the martian atmosphere Popova, O.P., Nemtchinov, I.V., Hartmann, W.K., 2003. Meteorit. Planet. Sci. 38, 905-925]. The second class is “large clusters” (D∼ few hundred m, spread over 2 to 30 km), which do not fit any predictions for breakup of known meteoroid types. We consider a range of possible explanations. The best explanation relates to known, high-speed ejection of large, semi-coherent, fractured rock masses from the surface, as secondary debris from primary impacts. The clusters are probably due to breakup of partly fracture, few-hundred-meter scale weak blocks, especially during ascent (producing moderate lateral spreading velocities among the fragments during sub-orbital flight), and also during descent of the resulting swarm. These conclusions illuminate the launch conditions of martian meteorites, including fragmentation processes, although more work is needed on the lateral separation of fragments (during either atmosphere descent or ascent) due to the effects of volatiles in the projectiles. Martian meteorites probably come from smaller martian craters than the clusters' source craters. The latter probably have D?85 km, although we have not ruled out diameters as small as 15 km. |
| Keywords: | Cratering Mars Meteorites Impact processes |
| 本文献已被 ScienceDirect 等数据库收录！ | |