NASA Technical Reports Server (NTRS) 20000062312: Rock Abrasion on Mars: Clues from the Pathfinder and Viking Landing Sites

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by  NASA Technical Reports Server (NTRS)

ROCK ABRASION ON MARS: CLUES FROM TRE PATHFINDER AND VIKING LANDING SITES. N. T. Bridgesl,
T.J. ParkerI, andG.M. Kramer2, tJetPropulsionLaboratoW,California Institute of Technology(MS 183-501, 4800 OakGrove
Drive,Pasadena, CA 91109; nathan,bridge_jpi.nasa.gov), _julversi Wof Minnesota, Minneapolis, MN 55414.
/ntroducr/on Methods
A significant discovery of theMarsPathfinder Based onprevious analyses of rover images, the
(MPF) mis_on was thatmanyrocks exhibit characteristics of width of most flutes atthePathfinder landing site isless than
ventifacts, rocksthathavebeen sculpted bysaltating parti- 2cm [2]. With IMP's resolution of Imrad/pixel and recog-
cles [1-3]. Diagnostic featuresidentifying therocks asventi. nizing thatflute widths must subtendatleast-10 pixels to be
facts are elongated pits,flutes, and grooves (collectively easily identified, only flutes within about 2mofthe lander
referredto as"flutes", unless notedotherwise). Faceted can be discerned. To increase the detail of fiutes visible in
rocksorrockportions,circularpits, rills, andpossiblypol- nominal resolution IMP images and toextend the range over
ishedrocksurfaces arealso seen and could bedue toaeolian which the flutes canbeidentified, "super-resolution" images
abrasion. Manyof these featmes were initially identified in were studied. Toproduce these images, multiple IMP frames
rover images, where spatial resolution generally exceeded ofthesame scene with sub-pixel offsets were co-added
thatofthe IMPOmager forMarsPathfinder)camera. [14,15]. Theresolution ofthese images is approximately
images hadtwo majorlimitations: 1) Only alimitednumber three timesthat of nominal IMP images. Thesesuper-
of rockswere viewed by therover, biasing flutestafistiea, resolution images were used toidentify flutes, aRerwhich
and2) Thehigherresolution obtained by therov_ images the 3-D location of the flute endpoints were located in
and thelack ofsuch pictures attheViking landing sites ham- nominal resolution stereo IMP images using theJPL-
pered comparisons ofrock morphologies between thePath- developed "Showstereo" prosram. The positions of theflute
finderandViking sites. Toavoid thislxoblem, rockmor- endpoints was thenconverted totrendandplunge.
phology and ventifact statistics have beenexamined using Todetermine ifventifacts were more abundantat
new"super-resolution" IMP andVikingLander images. the Pathfinder landingsitethanatthe Vikingsites, IMP im-
Analyses of these images show that 1)Flutes areseen on ages were compared to Vikinglanderframes.Thisapproach
about50*/0ormore of the rocks inthe nearfield at the MPF avoidedthebiasinherenitnusingclose-urpoverimages,
site2,) Theorientation oftbescfluteisssimilartothatfor which were notavailable forthe Vikingsites. IMP's nomi-
flutes iden_fied inrover images, and3) Ventifacts aresig- nalresolution of Imrad/pixel islessthanViking's 0.7
nificantly more abundant atthe Pathfinder landing sitethan mrad/pixel [16]. Therefore, super-resolution IMP images
atthe two Viking Landing sites, where rockshave undergone were degradedto Viking'rsesolution inorder toproduce
only alimited amountof aeolian abrasion. Thisismost comparable resolution images atall threelanding sites. At
likely duetothe ruggednesosftbePathfindersiteanda the presentlime, super-resolutViiokningimages arebeing
greatersupply of abradingparticles available shortly afterthe made and comparedtoun-degraded super-resolution IMP
Ares andTinValles outflow channel floods. images toidentifaydditional ventifacts inbothdatasets.
ThePathfinder and VitangLanding Sites Results
The Pathfinder and Viking landing sites are The dis_ibution of fluteorientations visible in
broadly similar, but exhibit important differences. Rock super-resolution images isshown in Figure I. Flutes were
abundances areabout 15"/,atallthree sites [4-6]. The soils foundon 19rocks, of which 2liein theNE quadrantand 17
of the sitesconsistof _ and more consolidated, soil-like intheSW quadrantA.ll the rocks haveradialpositions rela-
deposits [7]. A few Viking rocks areperebed onpedestals of tivetoIMP within04 rocks)orcloseto(3rocks)therange
soft,suggesting aeolian scour on the rocks'unde_ides, as ofmodem directioinnsdicatebdywindtailsw,indstreaks,
hasbeenobserved interrestrdieaslert[s81. Some possible andtheGeneralCirculatiMoondel[3,17,18]I.ftheflute
ventifacts inthe formof faceted rocks, flutes, andcircularto dim'ibutiownererandom,thenitwouldbeexpectedthat
elongated pitsaresuggested [8-11]. The vontifact-like forms flute statistics wouldbebiased toorientations radialfromthe
and scouring atthe Viking Landing sites imply that acofian IMP camera,inthiscasetheNE andSW quadrantsI.fthe
abrasion has modified these surfaces. Incontrast, the Patlv flutes were produced bythepresent wind regime, theclus-
finder site contains abundantventifacts, with50*/0ormore of teringwould be expected tobeeven greaterwithin these
the rockshaving undergone significaaneotlian abrasion quadrants. However, of the 35flutes measured so farinIMP
[1,2]. The ventifact featuresare most commonly inthe form images, 25(71%) areactually within theNW andSE quad-
of flutes. Atleast onerock, Yogi, lies onasoil pedestal, rants. Thisisindicative of winds blowing SE toNW or NW
which could have formed fromanolion scour. There isevi- to SE.
dence forsand-sizepdarticlaetsthePathfindelrandingsitien The abundanceofventifacattsthePathfinder
theformofbarchandunes[3]a,possiblbeasaltiscandor landingcanbegauged byexaminingFigure 2.Shown isa
granule armoronMermaid Dune [7],andlarger-scale dunes super-resolutIiMoPn imageoftbewesternpartoftheland-
visible in MOC images oftbe landing site. The Pathfinder ingsitecomparedtoViking-scalseuper-resolutainodn
site iswithin a depositional flood plain, where abundant nominalIMP resolution images.Preliminary studies have
sediment would beexpected after flood deposition, priorto examined thelanding site atViking-scalreesolutiotnhrough
removalbythewind. Incontrast,VL1 islocatedatthemore an azimuth range of 190° to275°. Although representing
distal margins of aflood plain whereas VL2 resides within lessthan aquarter of theentire site panorama,many venti-
knobby plains unaffected by large-scale fluvial activity facts arefound. Flutes me apparenton 19rocks, including
[12,13]. multiple flutes on Geordi(atleast 3), HalfDome (_>8), G-ar-
rak(> 3), Mohawk (>2), Cn'ommit (_>9), and an unnamed
ROCK ABRASION ON MARS: N.T. Bridges et al.
rook (> 4). Grooves are also apparent on Flat Top and Flute
Top. Other ventifact forms may be present, but to be conser- [I]N.T.Bridgesetal.,Lun.Planet.Scl.}(XIX,1530,1998.
vative, are not identified. About 50% of the rocks visible in
[2]N.T.Bridgesetal.,,/.Geophys.Res.,inpress,1999.[3]
super-resolution IMP images in the new field are ventifacts. R.Greeleyetal.£,.Geophys.Res.,inpress,1999.[4]M.P.
The multiple flutes and grooves visible at the Path- Golombek etal.,Saence,278,1758-1765,1997.[5]H.J.
finder site contrast with the rock textures atthe Viking sims. Moore andB.M. Jakosky,Icarus,81,164-184, 1989.[6]J.E.
Although some elongated pits are visible, even the best ex- Baron etal.,d.Geophys.Res.,103,22,695-22,712,1998.[7]
amples lack long flutes like those at the Pathfinder sire Rover Team, Science,278,1765-1768,1997.[8].J.F.
[8,10,11]. These observations strongly suggest that venti- M¢Cauley etal.,,L.Geophys.Res.,84,8222-8232,1979.[9]
facts are more abundant atthe Pathfinder landing site than at A.B.Binderetal.,J.Geophys.Res.,82,4439-445 I,1977.
the Viking sites. [I0]Mutch etal.,,LGeophys.Res.,82,4452-4467,1977.
[11]VikingLanderTeam, TheMartian Landscape, NASA
Discussion
Spec. Publ., SP-425, 160 pp., 1978. [12] D.H. Scott end K.L.
The identification of apredominance of SE-NW Tanaka, Geol. Map West. Eq. Mars, USGS Misc. Invest. Ser.
flute trends in the IMP images agrees with the flute trends Mapl-1802-A, 1986. [13] R_Greeley and J.E. Guest, GeoL
identified in rover images [1,2] and strongly suggests that Map East. Eq. Mars, USGS Misc. Invest. Ser. Map 1-1802-B,
vontifacts atthe Pathfinder landing site formed trader awind 1987. [14] T.J. Parker, Lunar Planet. Set. XXIX,, 1817, 1998.
regime different fyom that of today. The observations of [15] T.J. Parker, Fall AGU Meeting, Abstract 5470, 1998.
rock morphology atthe Viking sites gives insight into how [16] P.H. Smith et al., J. Geophys. Res., 102, 4003-4025,
the Pathfmder vontifacts formed. All three landing sites are 1997. [17] P.H. Smith et al., Science, 278, 1758-1765, 1997.
about the sere age and are therefore expected to have under. [18] J.B. Pollack etal., J. Atmos. Sc/., 38, 3, 1981. [19] J.T.
gone similar weathering events over time. This is especially Schofield et al., Science, 278, 1752-1758, 1997. [20] R.
true for MPF and VL1, which are only -800 km apart and Greeley and J.D. lversen, W#ndas a GeologtcalProcess, 333
have similar weather conditions [19]. Itis unlikely thatthe pp., Cambridge Univ. Press, New York, 1985. [21] SH.
rocks atthe MPF site are more susceptible to abrasion than Williams and J.A. Lee, J. AndEnv_ran., 30, 153-160, 1995.
rocks at the Viking sites, for ventifacts form on all major
rock types and pitted rocks, which are common at the Viking VentifactOrieotatlo_ (IMP Imaou)
sites, would be expected to evolve into ventifacts ifcondi- 0 II_ E_
tions were appropriate, just aspitted rocks on Earth do [20]. 330 30 _ .,.*.
Rather, the rook _ze distribution and the availabil-
ity of sand-sized particles are probably responsible for the
300 '" 80 "_ ._
pre_nce, characteristics, and orientatioonf ventifacts at the
Pathfinder site.The MPF siteismore ruggedandcontains
more tallrocksthantheVikingsims[I7].Grainssaltatinagt
• o,,4, _
greater heights shouldbeentrainedinhigher velocitywinds
for alonger time than grains atlower heights, increasing
their momentum and ability to abrade rock surfaces [20]• A
supply of abrading particles is an important factor controlling
aeolian transport and the formation of ventifacts on Earth
"_ ["i .m,Q,G_e
[20,21]. A large supply of sand-sized particles capable of " 7'3 '"
abrasion was probably deposited at the mouths of the
Ares/Tin channels, which formed in the late Hesperian to
early Amazonian (1•8-3.5 Ca). Because wind directions at Figure 1:Orientations of flutes seen m IMP images. Inthis
this time were probably different than winds of today and polar projection, flute azimuth in the up-plunge direction is
because any sand supply should bereduced or become ex- shown as the radial coordinate, with plunge being the cir-
hausted over time, abrasion by flood sediments is consistent cumferential coordinate. Lines projecting outward from the
with the discrepancy in wind directions derived from flutes edge of the plot show rock azimuth as viewed by IMP.
These lines and theassociated symbols for each rock are
versus those fi'om wind tails, wind streaks, and the general
shown in the legend. Solid arrows are minimum, average,
circulation model. This hypothesis also explains the relative
and maximum values of Iooal wind tail directions [3,17].
lack of ventifacts seen atthe Viking sites, where aputative
Arrow with large dashes represents the average trend of wind
ancient source of sediment is lacking. Ongoing and future streaks as seen in orbital images [3,17]. Arrow with small
studies of ventifacts at the three Martian landing sites should dashes isthe predominant wind direction predicted by the
yield additional important information on weathering proc- generalcirculatiomnodel [3,17,18].
esses andclimatechangeon Mars.
•_" -_'i-,-
Figure2:Examples ofventifactsseenatthePathfinderlandingsiteinnominal IMP resolution(left)s,uper-resolutiosncaled
toVikingLandercamera resolution(middle),and un-degradedsuper-resolutio(nright).These rocksarelocatedtothewestof
thelander.Ventifactswe identifiebdyarrowsinthemiddleframe.
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