1. PHOBOS GROOVES PHOBOS GROOVES A LUNAR ANALOGY Thomas Duxbury, GMU Gerhard Neukum, Freier Univ, and the MEX HRSC Team Mark Robinson, ASU, and the LRO LROC Team 12 OCT 2010 11st Moscow Solar System Symposium

2. PHOBOS GROOVES 12 OCT 2010 1st Moscow Solar System Symposium2 MEX SRC Image G. Neukum, PI Freie Univ

3. PHOBOS GROOVES PHOBOS GROOVE NETWORK 12 OCT 2010 1st Moscow Solar System Symposium3 Thomas, P. et al. (1979) JGR, 84, B14,. 8457–8477 Murray, J. et al. (2006) LPS XXXVII 2195 ANTI- STICKNEY

4. PHOBOS GROOVES POSSIBLE GROOVE ORIGINS Related to surface fractures of the interior generated by Mars tidal forces while undergoing large impacts Tidal stresses during capture into Mars orbit (if Phobos was an asteroid) Secondary craters chains from Phobos crater ejecta Crater ejecta rolling on the surface Secondary crater chains from Mars crater ejecta Thomas P, et al., Nature, 273, 1978 Head J, and M Cintala, PGP Report, 1979 Thomas P, et al., JGR, 84, B14, 1979 Murchie S, et al., LPS, XXXIX, 1434, 2008 Wilson L and J Head., LPS, XX, 1212, 1989 Murray J, et al., LPS, XXXVII, 2195, 2006 12 OCT 2010 1st Moscow Solar System Symposium4

5. PHOBOS GROOVES LUNAR ANALOGY 12 OCT 2010 1st Moscow Solar System Symposium5 LRO LROC NAC IMAGE: M. ROBINSON, PI, ASU http://lroc.sese.asu.edu/news/index.php?/archives/227-Hole-in-One!.html Boulder trail M122597190L 10 m Boulder

6. PHOBOS GROOVES LUNAR “GROOVES” KING CRATER 12 OCT 2010 1st Moscow Solar System Symposium6 M103717945R

7. PHOBOS GROOVES LUNAR “GROOVES” KING CRATER 12 OCT 2010 1st Moscow Solar System Symposium7 M103717945R

8. PHOBOS GROOVES LUNAR “GROOVES” Near Apollo 15 (25.65 N, 3.53 E) 12 OCT 2010 1st Moscow Solar System Symposium8 ~1 km #2 #1 #2 #1 M111571816R 80 m diameter crater 5 - 10 m diameter boulders

9. PHOBOS GROOVES LUNAR “GROOVES” Caused by Rolling Boulders from Crater Ejecta – Rolling boulder leaving trails seem to be more prevalent with oblique impacts, being ejected downstream in the direction of the more prominent ejecta blanket – Boulder’s longest (rotation) axis tend to stay normal to groove after reaching some level of rolling stability – Groove width ~ 60% of boulder length – Some boulders constantly stay in contact with surface – some hop Dependent on topography and axis of rotation – The lunar boulders travel downhill and their paths are effected by local topography and their rotation axis Can flip and hop on surface when long axes make surface contact 12 OCT 2010 1st Moscow Solar System Symposium9

10. PHOBOS GROOVES GROOVE ORIGIN Many Phobos grooves, the ones that follow the surface topography and cross other grooves, are possibly caused by rolling boulders ejected from Stickney impact at oblique angle from the west into regolith-covered rubble pile (if Phobos was accreted from Mars crater ejecta) – Eastern rim of Stickney is more pronounced with evidence of ejecta blanket causing color variation (CRISM, Murchie, et al., 2009,HiRISE, Thomas, et al., 2010) Boulders have significant rotational and local horizontal velocity and eventually escape the surface of Phobos near the Stickney antipodal point (only a few m/s required to escape) – Phobos orientation and rotation state at Stickney impact unknown Width of grooves proportional to length of boulders (most stable axis for rolling) Depth of groove related to regolith thickness / compaction, boulder rotational speed, friction between regolith and boulder, etc. 12 OCT 2010 1st Moscow Solar System Symposium10 NASA MRO HiRISE image of Phobos, McEwen, A., PI, U of AZ, http://hirise.lpl.arizona.edu/phobos.php The LRO LROC NAC and MEX SRC images provide an excellent dataset for comparative planetology studies on the possible origin of the Phobos grooves

11. PHOBOS GROOVES Comparative “Moon”ology 12 OCT 2010 1st Moscow Solar System Symposium11 Phobos groove network Lunar boulder trails