phobos grooves a lunar analogy
DESCRIPTION
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. PHOBOS GROOVES. MEX SRC Image G. Neukum, PI Freie Univ. PHOBOS GROOVE NETWORK. ANTI- STICKNEY. STICKNEY. - PowerPoint PPT PresentationTRANSCRIPT
PHOBOS GROOVES
PHOBOS GROOVESPHOBOS GROOVESA LUNAR ANALOGYA LUNAR ANALOGY
Thomas Duxbury, GMUGerhard Neukum, Freier Univ, and the MEX HRSC Team
Mark Robinson, ASU, and the LRO LROC Team
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PHOBOS GROOVES
PHOBOS GROOVESPHOBOS GROOVES
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MEX SRC ImageG. Neukum, PI Freie Univ
PHOBOS GROOVES
PHOBOS GROOVE NETWORKPHOBOS GROOVE NETWORK
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Thomas, P. et al. (1979) JGR, 84, B14,. 8457–8477Murray, J. et al. (2006) LPS XXXVII 2195
ANTI-STICKNEYSTICKNEY
PHOBOS GROOVES
POSSIBLE GROOVE ORIGINSPOSSIBLE 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, 1989Murray J, et al., LPS, XXXVII, 2195, 2006
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PHOBOS GROOVES
LUNAR ANALOGYLUNAR ANALOGY
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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
PHOBOS GROOVES
LUNAR “GROOVES”LUNAR “GROOVES”KING CRATERKING CRATER
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M103717945R
PHOBOS GROOVES
LUNAR “GROOVES”LUNAR “GROOVES”KING CRATERKING CRATER
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M103717945R
PHOBOS GROOVES
LUNAR “GROOVES”LUNAR “GROOVES”Near Apollo 15 (25.65 N, 3.53 E)Near Apollo 15 (25.65 N, 3.53 E)
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~1 km
#2 #1
#2
#2
#1
#1
M111571816R
80 m diameter crater
5 - 10 m diameter boulders
PHOBOS GROOVES
LUNAR “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
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PHOBOS GROOVES
GROOVE ORIGINGROOVE 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.
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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
PHOBOS GROOVES
Comparative “Moon”ologyComparative “Moon”ology
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Phobos groove network
Lunar boulder trails