Standardizing the Nomenclature of Martian Impact Crater Ejecta Morphologies

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Standardizing the nomenclature of Martian impact crater ejecta morphologies

Nadine G. Barlow University of Central Florida

Joseph M. Boyce

François M. Costard

Robert A. Craddock

James B. Garvin

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Recommended Citation Barlow, Nadine G.; Boyce, Joseph M.; Costard, François M.; Craddock, Robert A.; Garvin, James B.; Sakimoto, Susan E. H.; Kuzmin, Ruslan O.; Roddy, David J.; and Soderblom, Laurence A., "Standardizing the nomenclature of Martian impact crater ejecta morphologies" (2000). Faculty Bibliography 2000s. 2431. https://stars.library.ucf.edu/facultybib2000/2431 Authors Nadine G. Barlow, Joseph M. Boyce, François M. Costard, Robert A. Craddock, James B. Garvin, Susan E. H. Sakimoto, Ruslan O. Kuzmin, David J. Roddy, and Laurence A. Soderblom

This article is available at STARS: https://stars.library.ucf.edu/facultybib2000/2431 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 105, NO. Ell, PAGES 26,733-26,738,NOVEMBER 25, 2000

Standardizing the nomenclature of Martian impact crater ejeeta morphologies

NadineG. Barlow •, JosephM. Boyce2,Francois M. Costard3,Robert A. Craddock4, JamesB. Garvins, Susan E. H. Sakimotos,Ruslan O. Kuzmin6,David J. Roddy 7, and LaurenceA. Soderblom7

Abstract. The Mars CraterMorphology Consortium recommends the useof a standardized nomenclaturesystem when discussing Martian impact crater ejecta morphologies. The system utilizesnongenetic descriptors to identifythe variousejecta morphologies seen on Mars. This systemis designedto facilitatecommunication and collaborationbetween researchers. Crater morphologydatabases will be archivedthrough the U.S. GeologicalSurvey in Flagstaff,where a comprehensivecatalog of Martian cratermorphologic information will be maintained.

1. Introduction andFrawley, 1998; Gamin et al., 1999],and the generalgeologic history of the planet [Soderblomet al., 1974; Tanaka, 1986; Fresh Martian impact craters are typically surroundedby Barlow, 1988; Hartmann, 1999]. ejectastructures that differ in morphologyfrom the radial ejecta This articledescribes a systemof nomenclaturerecommended patternsseen around lunar and Mercurian craters. The Martian by the Mars Crater MorphologyConsortium for use when ejectastructures are typically composedof one or more layersof describing Martian impact structures. The Consortium, material, commonly displayed in a lobed pattern. These composedof this article'sauthors, met at the U.S. Geological structureshave been described by a number of adjectives, Surveyin Flagstaff,Arizona, in May 1998 and July 1999 to including fluidized, lobate, rampart, splosh, and flower. discussand developthese recommendations. The Consortium Although originally thoughtto be the result of wind erosionon membershave been actively involvedin utilizing Martian impact the basisof Mariner 9 image analysis[McCauley, 1973; Amidson cratersin a numberof studiesover the past20 years,and several et al., 1976], Viking Orbiter imagesrevealed that thesestructures haveproduced catalogs of cratercharacteristics. These databases were distributedglobally and likely the resultof emplacementby contain information that is often complementaryto but not fluidization processes,either from impact into and vaporization containedin the other crater catalogs. One of the goalsof the of subsurfacevolatiles [Cart et al., 1977; Wohletzand Sheridan, Mars CraterMorphology Consortium is to combinethe existing 1983] or by ejecta entrainmentby the thin Martian atmosphere crater databasesinto one system that can be queried for [Schultz and Gault, 1979; Barnouin-Jha and Schultz, 1998]. informationon crater location,size, shape,preservational state, Now as more details about the ejecta morphologies and ejectaand interiorstructures, and morphometriccharacteristics morphometriesbecome available becauseof the Mars Global (craterdepth, rim height,central peak height and width, central Surveyorand upcomingMars Surveyormissions, it is apparent pit diameterand depth, ejecta extent and sinuosity, etc.). Because that a standardizedsystem of nomenclatureis neededto facilitate of the variety of classificationsystems, many using different the exchangeof data between researcherswho compile crater terminologyto describethe samemorphology, the Consortium data for use in studies on erosional history [Craddock and agreedthat the first courseof actionwas to standardizethe Maxwell, 1990, 1993; Craddock et al., 1997; Grant and Schultz, nomenclaturefor cratermorphologic features. The first features 1990, 1993; Barlow, 1995; Hartmann and Esquerdo, 1999], to be standardizedare the ejectamorphologies. implicationsfor subsurfacevolatiles [Cintala and Mouginis- Mark, 1980; Mouginis-Mark, 1981, 1987; Kuzmin et al., 1988; Costard, 1989; Barlow and Bradley, 1990; Barlow, 1994; Boyce 2. Recommendations and Roddy, 1997; Costard and Gosset, 1998; Demura and Kurita, 1998], cratermorphometries and formation[Roddy, 1977; Martian ejecta blankets have been classified into many Cintala et al., 1976; Wood et al., 1978; Melosh, 1989; Gamin differentgroups because of the rangeof morphologiesidentified from the Viking Orbiter imagery. However, in general,the •Departmentof Physics, University of CentralFlorida, Orlando. morphologiescan be dividedinto threemain groups: 2Officeof SpaceScience, NASA Headquarters, Washington, D.C. 1. Layered ejecta patterns,where the ejecta blanket is 3CNRS/Laboratoirede GeologieDynamique de la Terre et des composedof one or more completeor partialsheets of material Planetes,Orsay, France. surroundingthe crater, appear to have been emplacedby 4Centerfor Earthand PlanetaryStudies, National Air and Space fluidizationprocesses, although some structures show evidence Museum,Smithsonian Institution, Washington, D.C. 5NASAGoddard Space Flight Center, Greenbelt, Maryland. of subsequenteolian erosion. 6VernadskyInstitute, Russian Academy of Sciences,Moscow, Russia. 2. Radial ejecta blankets,which are similar to the ejecta 7U.S.Geological Survey, Flagstaff, Arizona. patternsaround lunar and Mercuriancraters, are believedto be emplaced by secondarymaterial ejected along ballistic Copyright2000 by the AmericanGeophysical Union. trajectories. Papernumber 2000JE001258. 3. Combination structuresshow both layered and radial 0148-0227/00/2000JE001258509.00 patterns.

26,733 26,734 BARLOW ET AL.: MARTIAN IMPACT CRATER NOMENCLATURE

Table 1. Correlationof New MorphologyTerminology With PreviousNomenclature

Nomenclature Reference

Layered Ejecta Structures Pedestal(P) Pedestal McCauley [ 1973] Pedestal Amidsonet al. [ 1976] Pedestal Head and Roth [1976] Mound Johansen[1979] Lump Johansen[ 1979] Single-layerpancake (SLEPC/SLEPS) Polar Johansen[ 1979] Type 6 Mouginis-Mark[ 1979] SS Horner and Greeley[ 1987] Type 3 Costard[1989] Pancake Barlow and Bradley [ 1990] Single-layerrampart (SLERC/SLERS) Type 1 Mouginis-Mark[ 1979] Class4 Blasiusand Cutts [1980] SR Horner and Greeley[ 1987] Type 1/flower Costard[1989] Singlelobe Barlowand Bradley[ 1990] Double-layerrampart (DLERC/DLERS) Composite Johansen[ 1979] Type 2 Mouginis-Mark[ 1979] Class3 Blasiusand Cutts [1980] D Horner and Greeley[ 1987] Type 2/rampart Costard[1989] Double lobe Barlow and Bradley [1990] Multiple-layer rampart(MLERS) Flower Johansen[1979] Type 3 Mouginis-Mark[ 1979] Class2/flower Blasiusand Cutts [ 1980] MR Horner and Greeley[1987] Multiple lobe Barlowand Bradley [1990]

Radial Morphologies Radial (SLER) Lunar riohansen[1979] Class 1/lunar Blasiusand Cutts [1980] Type 4 Mouginis-Mark[ 1979] Radial Barlow and Bradley [1990]

CombinationMorphologies (e.g., SLERSR) Transitional riohansen[ 1979] Type 5 Mouginis-Mark[ 1979] Diverse Barlow and Bradley [ 1990]

Table 1 providesa listing of someof the terminologythat has 3. Layered ejecta craterssurrounded by three or more beenused to describecraters in thesebasic groups. completeor partiallayers of materialshall be called"multiple- The Mars Crater Morphology Consortiumrecommends the layer ejecta"(MLE) (Figure l d). following changesin nomenclature: 4. The single-layer, double-layer,and multiple-layer First, layered ejecta patternsthat have undergonesubstantial categoriesare further modified by termsdescribing the shapeof erosionowing to eolian activity, resultingin the craterand ejecta the ejectaterminus. Those layered ejecta patterns terminated by being perchedabove the surroundingterrain, shall be referredto a distalridge or rampartshall be modifiedby theterm "rampart" as "pedestalcraters" (Pd). The ejectablanket of a pedestalcrater (R) (i.e., Figure l d). Hence a single-layeredejecta pattern is typified by a sharpedge (no distal ridge) that dropsoff to the terminatedin a distalridge would be calleda "single-layerejecta lower elevationof the surroundingterrain (Figure l a). rampart." Layeredejecta patterns that terminatein a concave Second, other layered ejecta patternsshall be referred to as slopewill bemodified by theterm "pancake" (P) (Figure1 e). "layeredejecta craters" (LE). 5. The rampartand pancake terms are further modified by the 1. Layered ejectacraters surrounded by only a singlelayer of adjectives"sinuous" (S) (i.e., Figurel d) and"circular" (C) (i.e., materialshall be called"single-layer ejecta" (SLE) (Figure lb). F•igure1e), describingthe general sinuosity of theejecta blanket. 2. Layered ejectacraters surrounded by two layersof material Ideally,the designationof S versusC will be basedon an actual shall be called "double-layerejecta" (DLE). The inner layer of quantitativemeasurement of the ejectasinuosity, such as the the DLE morphologyhas a smaller diameterthan the outer layer lobatenessmethod describedby Barlow [1994]. Using the and is usuallysuperposed on the outerlayer (Figure 1c). lobatenesssystem, ejecta morphologies with lobatenessvalues BARLOW ET AL.' MARTIAN IMPACT CRATER NOMENCLATURE 26,735

.. ..

ß . :...,•::'½::::i'::::;ii:::•:..-':':.;':..•;..;: '..:...':2:: :.:::..::5 ;:.:::

Figure 1. Examplesof the new ejectamorphology classifications recommended by the Mars Crater Morphology Consortium. Arrows point to the distinguishingejecta features. (a) A 1.5-km-diameterpedestal (Pd) crater, located at 11.4øN, 161.5øW, (Viking Orbiter image 886A09). (b) Two single-layerejecta rampart sinuous (SLERS) craters. The top crateris 18.1 km in diameterand locatedat 8.80øN, 72.13øW. The bottomcrater is 18.9 km in diameterand locatedat 7.96øN, 72.16øW (Viking Orbiter image 858A56). (c) A 9.6-km-diameterdouble- layer ejectarampart sinuous (DLERS) crater,located at 21.42øN, 79.02øW (Viking Orbiter image 555A24). IL identifiesthe inner ejectalayer; OL denotesthe outerejecta layer. (d) A 33.9-km-diametermultiple-layer ejecta rampartsinuous (MLERS) crater,located at 26.59øN, 38.55øW (Viking Orbiter image 827A01). IL indicatesthe inner ejectalayer, ML identifiesthe middle ejectalayer, and OL denotesthe outer ejecta layer. (e) A 7.7-km- diametersingle-layer ejecta pancake circular (SLEPC) crater,located at 26.10øS,69.04øW (Viking Orbiter image 608A29). (f) Single-layerejecta radial (SLERd) craters. The large crateron the left is 75.3 km in diameterand locatedat 24.36øN, 10.79øW (MDIM image Mg25n012). (g) A 107.2-km-diametersingle-layer ejecta rampart circularradial (SLERCRd) crater,located at 32.32øN,337.9øW (MDIM imageMg30n337). Rd indicatesthe radial componentof the ejectablanket, while SLER identifiesthe single-layerejecta rampart portion of the blanket.

<1.5 would be classifiedas circular, while those with larger Third, following the above nomenclatureprocedure, radial lobateness values would be defined as sinuous. Thus a crater ejecta patternswill be referredto a "single-layerejecta radial" identifiedas being surroundedby a single-layerejecta rampart (SLERd) (Figure I f). with a lobatenessvalue of 2 would be classifiedas single-layer Fourth, combinationpatterns (Figure l g) will be denotedby ejectarampart sinuous (SLERS). combiningthe abovenomenclature. For example,a single-layer 26,736 BARLOW ET AL.' MARTIAN IMPACT CRATER NOMENCLATURE

53 WeslLongitude 52 25ß. I - I __. i'Orbit Track Coverage ,I .

• 24

MOLA Topography [rnl

-2500

11346 10 km -3500

307 307.5 308 308 5 23 East Longitude 307 308 East Longitude i.-C -K• approximateextentofvisible radialeJecta • : &-2200

"- -2600 o

o F- -3000

-3400 :..._v.,.,-,o ! , L./'",,J , 23 23.5 24 245 Latitude

Plate 1. Viking Mars Digital Image Mosaic(MDIM), Mars OrbiterLaser Altimeter (MOLA) topographicprofile, and digital elevationmodel (DEM) for the 20-km "radial ejecta"impact crater Poona, located at 24øN, 52.5øW. (a) Viking MDIM of Poonaat a resolutionof 256 pixelsper degree,with superimposedMOLA centerlinepass (in yellow) from MGS orbit 1346. The inset showsPoona in the high-resolution(43 m/pixel) Viking Orbiter image F0022A54. (b) Topographicgrid of Poona with a resolutionof 64 pixels/degreein longitude and 256 pixels/degreein latitude. The grid includesMOLA datathrough MGS orbit 5507 (early June2000), and the orbit track coverageis shown,with localprecision in the submeterrange. (c) Full-resolutionMOLA centerlineprofile, showingthe grosscrater topography as well as the topographicallysubtle (40-80 m) expressionof ejectaramparts (indicatedwith arrows)within the radial ejectablanket visible in the Viking image, and the asymmetriccentral peak and inner cavity wall terraces. BARLOW ET AL.: MARTIAN IMPACT CRATER NOMENCLATURE 26,737 rampart ejecta with sinuous ejecta that has a radial pattern images. As an example, the classicradial ejecta crater Poona, superposedon it (i.e., the "diverse" morphologyin the Barlow located at 24øN, 52.5øW, is shown in Plate 1. This 20-km and Bradley [1990] nomenclature)will be called "single-layer complex impact crater displays an irregular central peak, is ejectarampart sinuous radial" (SLERSRd). surroundedby a radially striatedejecta reminiscent of somelunar The correlation of the old terminology and the new ejecta patterns, and appearsto be relatively nondegradedin nomenclatureis shown in Table 1. This nomenclaturemay higher-resolutionViking-era images(Plate 1). However, as the appearunwieldy upon first use. The Mars Crater Morphology MOLA centerline topographic transect reveals, the ejecta Consortiumdiscussed this issuebut decidedthat this systemis associatedwith this feature is layered, with a clearly defined the most conciseway of describingthe large variety of ejecta rampartat the distalmargin, as is typical for many of the impact morphologiesfound aroundMartian impactcraters. This system featuresin the northernpolar latitudeson Mars. The cratercavity also is flexible enoughthat future classificationsthat may arise is noticeably"U-shaped," beyond that which is most commonly due to the incorporation of new data (see next section on observedfor similarly sized impact featureson Mars [Gamin et topographyfor an example) can be easily accommodated.The al., 2000]. The depth-to-diameterratio, or d/D, is 0.058, which Consortium agreed that morphological nomenclature should atteststo the pristine characterof this crater. Finally, the avoid referencesto possible origins of these structures;thus thicknessof the ejecta blanket decayssharply, with an exponent "fluidized" and "ballistic" terms were rejected in favor of the of-8.5, which is far in excessof the-3.0 ejecta decay exponent nongenetic"layered" and "radial"terminology. favored by previous workers for pristine lunar style impact The Mars Crater Morphology Consortiumrecognizes that craters [McGetchin et al., 1973]. These new measurementsfor some researchersmay find this recommendednomenclature this one example of a well-analyzedimpact crater suggestthat restrictive and unusable for a particular project. In such anotheriteration of the Martian crater classificationscheme may situationsthe researchersare encouragedto developtheir own be required by the time subkilometer-scaleDEMs are available system that will facilitate their analysis. However, upon for virtually all complex Martian impact craters. The archiving of the database, the researchersshould indicate as combination of high vertical resolution DEMs from MOLA, closely as possible how their system correlates with the together with 2 to 5 m/pixel imaging from the Mars Orbiter recommendednomenclature system so comparisonswith other Camera(MOC), shouldallow for refinementsto the classification databases can be facilitated. presented herein. This is not to suggest,however, that the morphologicclassification cannot stand on its own. 3. Effect of Topography on Morphology Thus, the new perspectivethat is soonto be providedglobally Classifications by MOLA for Martian impactcraters should permit refinementof The morphologicclassification recommendations presented existingmorphologic classification approaches. The benefitsof a hereindepend almost exclusively on moderateto high spatial combined morphologic-morphometricapproach will then be resolutionimaging data. An additionalperspective is rapidly possible. Such an approach will facilitate developmentof becomingavailable as the spatial density of orbitallaser altimetry improvedphysical models of the ejecta emplacementand cavity that is currentlybeing acquiredby the Mars Orbiter Laser growth processesassociated with hypervelocityimpact cratering Altimeter(MOLA), a topographicprofiling instrument aboard the under Martian conditions. Ultimately, the combined Mars Global Surveyor(MGS), increases.Subkilometer spatial classificationwill permit the effect of target variables in space resolution digital elevation models (DEMs) with vertical and time to be unraveled. MOLA DEMs for over 5000 impact accuraciesas fine as 2-3 m RMS are now routinelyachieved craters catalogedin the existing Barlow [2000] databasehave usingMOLA datafor the middleto higherlatitudes of Mars. In been constructedand measuredat the time of writing, and several addition,virtually all impactfeatures larger than approximately thousandmore will be measuredby the end of this year. 10-15km havebeen traversed by at leastone MOLA topographic transect. Thesetransects provide highly preciseinformation on 4. Database Archiving crater geometricproperties, many of which were previously unmeasurable or unmeasured. MOLA crater transects allow for The primary purpose of recommending standardsfor the nomenclatureof ejecta morphologiesis to facilitate the cross- determinationof craterdepth, cavity cross-sectional shape, ejecta utilization of different crater data sets. All members of the Mars thicknessfunction characteristics,inner cavity wall slopes, Crater Morphology Consortium who have developed such terracegeometry, ejecta flank slopes,and manyother properties. catalogsof craterdata have agreedto updatetheir databasesusing An initialsummary of someof thesenewly measured parameters the new nomenclature. They also have agreed to archive their is given by Garvin and Frawley [1998], and interpretationof data sets at the U.S. Geological Survey in Flagstaff, where north polar region cratersusing MOLA transectsis given by computerstaff will combinethe datasets into one comprehensive Garvin et al. [2000]. crater catalog. Any inconsistenciesbetween the data setswill be In three dimensions,impact craters on Mars remain an resolved by the compilers of the affected data sets. This incrediblydiverse population, with subtletiesthat are not yet comprehensivecatalog of Martian impact crater characteristics captured by existing morphologic classification schemes. will be formatted for use with the Arc/Info and Arcview GIS Virtually all topographically"fresh" impact featuresdisplay systems[Roddy et al., 1998a, 1998b]. someform of distalrampart, at what appearsto representthe Any researcherswho wish to contribute data sets to this distalmargin of a continuousejecta blanket. In manycases this comprehensivecatalog should contact the U.S. Geological elevatedor upturnedmargin displays very subtle relief with only Survey for information on the necessaryformatting. Submitted 10-30 m of expression.For the first time, MOLA DEM format data will be reviewed for contentby membersof the Mars Crater dataallow for refinedapproximation of the preimpactsurface in Morphology Consortium prior to acceptance into the the form of a referenceplane againstwhich to referencesuch comprehensivecatalog. measurementsas mean rim height, rampart relief, and many others.Layered morphologies display geometric properties that Acknowledgments. The authorsthank James J. Frawley, Marin are as diverseas those that canbe discernedfrom high-resolution Wong, and Greg Neumann for their assistancein the MOLA data 26,738 BARLOW ET AL.: MARTIAN IMPACT CRATER NOMENCLATURE

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