Update on the Geological Mapping of Dwarf Planet Ceres from NASA's

3rd Planetary Data Workshop 2017 (LPI Contrib. No. 1986) 7006.pdf

UPDATE ON THE GEOLOGICAL MAPPING OF DWARF PLANET CERES FROM NASA’s DAWN MISSION. D. A. Williams, and the Dawn Science Team, School of Earth & Space Exploration, Arizona State Uni- versity, Box 871404, Tempe, AZ 85287 ([email protected]).

Introduction: NASA’s Dawn spacecraft arrived at a Special Issue of Icarus to be published in 2017, in dwarf planet Ceres on March 5, 2015. As part of the which the individual quadrangle map papers are under Ceres orbital mission, the Dawn Science Team insti- review (as of April 2017). In the following sections we tuted a geological mapping campaign, building on the highlight some of the key results from several of our successful mapping campaign for asteroid (4) Vesta quadrangle maps. [1]. In this abstract I report on the current progress of Kerwan Quadrangle. The 284-km diameter Ker- the Ceres mapping campaign. wan impact basin (center 10.77˚S, 123.99˚E) is the Data for Mapping: Dawn’s Nominal Mission at largest indisputable and oldest impact crater on Ceres, Ceres [2] consisted of operations in four orbital phases: based on 1) the degradation state of its rim [6, 7] and Approach (Framing Camera (FC) spatial resolution 10- the lack of any identifiable ejecta from Kerwan, sug- 1.3 km/pixel), Survey (415 m/pixel), High Altitude gesting the terrain has been gardened to the point Mapping (HAMO, 140 m/pixel), and Low Altitude where Kerwan is indistinct from the surrounding cra- Mapping (LAMO, 35 m/pixel). Geologic feature iden- tered terrain; 2) the lack of any larger, definitive im- tification on Ceres began during approach, and a series pact craters [8]; 3) preliminary crater size-frequency of geologic maps are being generated using FC image distribution measurements of ‘smooth’ material in and basemaps and stereo-based digital terrain models surrounding the Kerwan basin, indicating it is the old- (DTMs) from Survey, HAMO, and LAMO orbits. The est unit outside of the ‘cratered terrain’ that makes up first Survey-based geologic map was published in [3]. most of Ceres’ crust [7]; and 4) modeling suggesting HAMO-based Global Map: Dawn at Ceres Guest that the Kerwan basin has undergone considerable vis- Investigator Scott C. Mest is leading the effort to con- cous relaxation compared to Ceres smaller craters, struct a global geologic map based on HAMO images. suggestive of advanced age [6]. Crater counts of the This map not only describes the global geology of ‘smooth’ material within and around the Kerwan basin Ceres, but also includes a preliminary Ceres chronos- indicate an absolute model age (AMA) of 1.30 Ga tratigraphy and geologic time scale developed from (Lunar-Derived chronology Model, LDM: [7]) and work by the whole Science Team. For details on the 0.27 Ga (Asteroid-Derived Model, ADM: [7]). Alt- HAMO global map, see the LPSC abstract by Mest et hough there are no contact relations between Kerwan al. [2017]. and Yalode basin materials, based on our current crater LAMO-based Quadrangle Maps: The surface of counts of their ejecta blankets, we infer that Kerwan is Ceres was divided into 15 quadrangles to aid in carto- older than Yalode, and that the Kerwan impact event graphic processing of Framing Camera images [4], and marks the base of the cerean geologic timescale, sepa- these 15 LAMO-based image quadrangles served as rating the Pre-Kerwanan cratered terrain from younger basemaps for our high-resolution geologic mapping. Kerwanan materials [9]. The goal of this mapping campaign was to conduct Urvara-Yalode Quadrangles. Urvara (170 km di- detailed geological studies of interesting rea- ameter) and Yalode (260 km diameter) are adjacent gions/features on Ceres to aid in determination of impact basins in Ceres’ southern hemisphere. Cross- Ceres geologic history, and to provide geologic context cutting and superposition relations show that Urvara to support analyses of the Visible and Infrared spec- superposes Yalode, that their ejecta blankets are com- trometer (VIR) and Gamma Ray and Neutron Detector plexly intermingled, and that large areas of smooth (GRaND) and gravity data sets. Preliminary geological material now cover much of their floors and extend maps were presented as a series of 14 posters at the beyond their rims, with some possible evidence of lo- 47th LPSC. Since March 2016 we have received final calized ice-rich flows. AMAs of their ejecta blankets FC image mosaics, revised DTMs, and preliminary indicate Urvara formed ~120-140 Ma (LDM) whereas VIR data to complete final ‘nominal mission’ versions Yalode formed ~1.1 Ga or earlier (LDM) [10]. For of our quadrangle-based geologic maps. All mapping additional details see the LPSC abstract by Crown et is being done using ArcGIS™ software. Generating al. [2017]. consistent project data (w.r.t. structure and geometry) Occator Quadrangle: Occator Quadrangle has four and comparable map sheets (w.r.t. cartographic sym- large craters that have fractured, shallow floors, mor- bology) required creation of a GIS template [5]. The phologically similar to lunar floor fractured craters. map results are being included in a series of papers for The fractures are interpreted to be caused by uplift 3rd Planetary Data Workshop 2017 (LPI Contrib. No. 1986) 7006.pdf

from cryomagmatic plumes. The 92 km diameter crater together the 15 quadrangle maps in ArcGIS™ to make Occator is well known for its bright spots, now named a final LAMO-based global map of Ceres (Figure 1). Cerealia Facula (central bright spot) and Vinalia Facu- This will be made freely available by the Dawn Sci- lae (eastern bright spots). The Vinalia Faculae occur ence Team, and will serve as the definitive map until a over the Occator floor fractures, thought to be the USGS-publishable global map of Ceres can be pro- source vents for explosive cryovolcanic venting (for posed to NASA, probably in 2018. more details, see the abstract by O. Ruesch et al. [this References: [1] Williams, D.A. et al. (2014) Ica- meeting]. Cerealia Facula may also have had explosive rus, 244, 1-12. [2] Russell, C.T. and Raymond, C.A. venting, but is dominated in its center by a ~2 km di- (2011) Space Sci. Rev., 163, 3-23. [3] Buczkowski, ameter dome within a 9 km wide central pit [11], inter- D.L. et al. (2016) Science, 353, preted as an extrusive cryovolcanic construct [12]. dx.doi.org/10.1126/science.aaf Haulani Quadrangle: 34 km diameter Haulani 4332. [4] Roatsch, T. et al. (2016) PSS 129, 103-107. crater is one of the youngest features on the surface [5] Nass, A. et al. (2017) LPSC, this meeting. [6] (~1.7-2.5 Ma, both chronology systems). This crater Bland, M.T. et al. (2016) Nat. Geosci., 9, 538-542. [7] displays distinctive rays and a bright ejecta blanket, as Hiesinger, H. et al. (2016) Science, 353, well as a complex interior morphology including ter- dx.doi.org/10.1126/science.aaf4759. [8] Marchi, S. et races, a central peak, and both smooth and hummocky al. (2016) Nat. Comm., dx.doi.org/10.1038/ncomms floor materials. Lobate materials suggest ice flows or 12257. [9] Williams, D.A. et al. (2017) Icarus, in re- possibly cryovolcanic flows [13]. view. [10] Crown, D.A. et al. (2017) Icarus, in review. Endgame: Once final revisions to the quadrangle [11] Schenk, P. et al. (2015) EPSC EPSC2015-400. maps have been completed, and all of the quadrangle [12] Buczkowski, D.L. et al. (2017) Icarus, in review. mapping papers have been accepted, we will merge [13] Krohn, K. et al. (2017) Icarus, in review.

Figure 1. First conversion of 8 of 15 LAMO-based quadrangle maps of dwarf planet Ceres into one single geologic map (imaged as Molleweide projection). This matching was implemented by the help of the predefined ArcGIS™ template. NOTE: These quadrangle maps are undergoing peer review, and will be adapted and updated before final publication. GIS processing and cartographic support by Andrea Nass, DLR.