P UBLIC ATIO N S Geo physical Research Letters RESEARC H LETTER Pitte d terrai ns o n (1) Ceres a n d i m plicati o ns f or s hall o w 10.1002/2017 GL073970 s u bs urface v olatile distri b uti o n Key P oi nts: H. G. Size m ore 1 , T. Pl atz 2 , N. Schorghofer 1 , T. H. Pretty ma n 1 , M. C. De Sa nctis 3 , • Fresh co mplex craters on Ceres host 1 4 4 4 5 6 disti nctive pitte d terrai ns t hat are D. A. Cr o w n , N. Sch mede mann , A. Neese mann , T. K n eissl , S. Marc hi , P. M. Sc he nk , m or p h ol o gi c all y si mil ar t o pitt e d M. T. Bl a n d 7 , B. E. Sc h mi dt 8 , K. H. G. Hughson 9 , F. T osi 3 , F. Za mbon 3 , S. C. Mest 1 , materials on Mars an d Vesta R. A. Yi n gst 1 , D. A. Willi a ms 1 0 , C. T. R uss ell 9 , and C. A. Ray mond 1 1 • Pitte d terrai ns o n Ceres likely f or m via t he ra pi d v olatilizati o n of m olec ular 1 Pla netary Scie nce I nstitute, Tucso n, Arizo na, US A, 2 Max Planck Institute for Solar Syste m Research, Göttingen, Ger many, H 2 O e ntrai ne d i n i m pact materials 3 4 • Pitted terrains may be co m mon Istit ut o di Astr o fi si c a e Pl a n et ol o gi a S p azi ali, I N A F, R o m e, It al y, De part ment of Eart h Scie nces, Freie U niversität Berli n, 5 6 m or p h ol o gical markers of v olatile-ric h Berli n, Ger ma ny, South west Research Institute, Boul der, Colora do, US A, Lu nar a n d Pla netary I nstitute, Housto n, Texas, near-s urface material i n t he aster oi d U S A, 7 US GS Astrogeology Science Center, Flagstaff, Arizona, US A, 8 Depart ment of Planetary and Space Physics, Georgia b elt I nstitute of Tec h nolo gy, Atla nta, Geor gia, US A, 9 De part ment of Eart h, Pla netary, a n d S pace Scie nces, U niversity of Califor nia Los A n geles, Los A n geles, Califor nia, US A, 1 0 School of Earth an d S pace Sciences, Arizona State University, Te m pe, Arizona, 1 1 Supporting Infor mation: U S A, Jet Pro pulsio n La boratory, Califor nia I nstitute of Tec h nolo gy, Pasa de na, Califor nia, US A • Supporting Infor mation S1 • Supporting Infor mation S2 A bstract Prior to the arrival of the Da wn spacecraft at Ceres, the d warf planet was anticipated to be Correspondence to: ice-rich. Searches for morphological features related to ice have been ongoing during Da wn ’s missi o n at H. G. Siz e m or e, Ceres. Here we re port t he i de nti fi catio n of pitte d terrai ns associate d wit h fres h Cerea n i m pact craters. T he size more @psi.edu Cerea n pitte d terrai ns ex hi bit stro n g mor p holo gical si milarities to pitte d materials previously i de nti fi e d o n Mars ( where ice is i mplicated in pit develop ment) and Vesta ( where the presence of ice is debated). We Cit ati o n: e mploy nu merical models to investigate the for mation of pitted materials on Ceres and discuss the relative Size m ore, H. G., et al. ( 2 0 1 7), Pitte d ter- rai ns o n (1) Ceres a n d i m plicati o ns for i m portance of water ice an d other volatiles in pit develo p ment there. We conclu de that water ice likely plays s hall o w s u bs urface v olatile distri b uti o n, an i mportant role in pit develop ment on Ceres. Si milar pitted terrains may be co m mon in the asteroid belt Ge o p hys. Res. Lett. , 4 4 , 6570 – 6 5 7 8, an d may be of interest to future missions motivate d by both astro biology an d in situ resource utilization. doi:10.1002/2017 GL073970. Received 26 APR 2017 1. I ntr o d ucti o n Accepted 22 J U N 2017 Acce pte d article online 27 J U N 2017, The Da wn spacecraft entered orbit around d warf planet Ceres on 5 March 2015. Over the fi rst 16 months at Published online 15 J UL 2017 Ceres, the s pacecraft o btaine d mor phological, to pogra phical, mineralogical, ele mental, an d gravity data fro m a series of successively lo wer orbits. Fra ming Ca mera (FC) i mages fro m high altitude mapping orbit ( H A M O) and lo w altitude mapping orbit (L A M O) have provided global coverage of Ceres ’ s urface at pixel scales of 140 m/pixel and 35 m/pixel, respectively. In the FC data set we have identi fi e d disti nct pitte d terrai ns, characterized by clusters of round-to-irregular, apparently ri mless pits in s mooth i mpact materials. We descri be t he mor p holo gy, setti n g, a n d geo gra p hic distri butio n of t hese terrai ns, w hic h ex hi bit striki n g si mi- larities to pitte d materials previously discovere d by Da w n at Vesta [ De nevi et al ., 2 0 1 2; Re d dy et al. , 2012] a n d pitte d materials i de nti fi e d in lo w- an d mi d dle-latitu de Martian craters [ Tornabene et al ., 2 0 1 2; B oyce et al ., 2012]. We discuss likely for mation mechanis ms for the Cerean pitted materials, as well as i mplications for the geogra phic distri bution an d concentration of shallo w volatiles on Ceres. 2. Methods Pri or t o Da w n ’s arrival at Ceres it was a ntici pate d t hat t he d warf pla net ’s o ut er s h ell mi g ht b e w at er ic e-ric h [ e. g., McCord and Sotin , 2005, and references therein]. Further, ther mal si mulations predicted that ice in the shallo w subsurface could be protected against subli mation on billion year ti mescales by a dry silicate lag, varying in depth fro m tens or hundreds of meters near the equator to centi meters near the pole [e.g., ©2017. The Authors. Fanale and Salvail , 1989; Schorghofer , 2008, 2016]. Using FC i mages, we have carried out global searches T his is a n o pe n access article u n der t he for mor phological features that are potentially diagnostic of the presence of su bsurface ice base d on analo- ter ms of the Creative Co m mons Attribution- NonCo m mercial- No Derivs gies wit h a variety of s olar syste m o bjects [e. g., Sc h midt et al ., 2017]. Feat ures of partic ular i nterest i n t his Lice nse, w hic h per mits use a n d distri- search were pits and depressions, which have been linked to gas-phase volatile loss on Mars, Callisto, bution in any mediu m, provided the Euro pa, Mercury, Vesta, Trito n, a n d Pluto. We carrie d out a glo bal searc h for pits a n d de pressio ns duri n g eac h ori gi nal w ork is pr o perly cite d, t he use is non-co m mercial and no modi fi cati o ns mapping orbit (Survey, HA M O, and LA M O). Because Ceres ’ surface morphology is do minated by i mpact or a da ptations are ma de. structures, distinguishing bet ween features produced by volatile loss and features produced by pri mary SIZE M ORE ET AL. PITTE D TERR AI NS O N (1) CERES 6570 Geo physical Research Letters 10.1002/2017 GL073970 a n d seco n dary i m pacts was a n o n goi n g co nsi deratio n i n our a nalysis of F C data. Our criteria for i de nti fi c ati o n of pits, de pressi o ns, a n d pit cl usters releva nt t o v olatiles were t he prese nce of (1) ri mless de pressi o ns, wit h (2) round-to-irregular, elongate, branching, or polygonal margins, and exhibiting (3) overlapping or repeating patter ns. T hese criteria were base d pri marily o n c haracteristics of t he Martia n “S wiss Cheese ” an d dissecte d ma ntl e t errai ns [ M ali n et al ., 2 0 0 1; Millike n a nd Mustard , 2 0 0 3; Byr ne a nd I ngersoll , 2003], the morphology of pitted materials inferred to be volatile-rich in craters on Vesta, Mars, and Mercury [ De nevi et al ., 2 0 1 2; Tornabene et al ., 2 0 1 2; Ble wett et al ., 2011], and revie ws of ice subli mation as a geo morphic process [e.g., Mangold , 2 0 1 1; M o ore et al ., 1996].