High-Resolution Geologic Mapping of Urvara Crater, Ceres: Basemap, Crater Counting, and Feature Maps H. G. Sizemore1, D. P. O’Brien1, A. Neesemann2, D. A. Crown1, D. C. Berman1, D. L. Buczkowski3, and J. E. C. Scully4. 1Planetary Science Institute ([email protected]), 2Freie Universität Berlin, 3Johns-Hopkins University Applied Physics Laboratory, 4Jet Propulsion Laboratory.

Introduction & Motivation Crown et al. 2018 The C2E Mosaic We are developing a detailed geologic map and accompanying chronostratigraphy of Urvara crater, Ceres, based on high-resolution image data (C2E; 3.5-20 m/px) acquired at the end of the Dawn mission. Crater BASEMAP DEVELOPMENT: diameter: 170 km. Map region: -128to -93E longitude, -59to -35N latitude. Publication scale:

1:250,000. Digitization scale: 1:50,000. ! ~1600 Level 2b images at resolutions down to ~3-4 m/px, ~1200 are better C Cryovolcanism has been a topic of ongoing interest on Ceres. Three locations on the dwarf planet have been than 10 m/px identified as regions of potential recent extrusion: Ahuna Mons [1], Occator crater [2], and Urvara crater [3]. ! Image-to-image control points found The C2E data provides ~75% coverage of the Urvara interior at <20 m/px and nearly 30% coverage at <5 with ISIS “findfeatures” routine m/px. Detailed mapping of Urvara will allow us to (1) test the cryovolcanic hypothesis at Urvara for the first time and (2) build global context for analysis done at Occator and Ahuna. Constraining the timing of crater ! Ground control points manually floor modification at Urvara also has the potential to disambiguate the rapid evolution of impact-induced added to tie images to DLR LAMO B melts from the emplacement of more deeply sourced material and recent mass wasting. basemap A

! Bundle adjustment with ISIS “jigsaw” routine to update pointing Ahuna Mons Cerealia facula, Occator Urvara crater ! Side benefit: Updated SPICE CK and SPK kernels generated for all component images from updated pointing info! ~20 km 3 km ~170 km ! Photometric correction, map projection (polar stereo at 5 m/px), D Crown et al. [3] previously mapped the Urvara-Yalode region using Low Altitude Mapping Orbit data (35 m/px). and mosaicking ! In general, highest resolution images placed on top

! Final result: ~40000x57000 pixel Preliminary Crater Counts & Age Estimates mosaic at 5 m/px resolution

AT RIGHT: We have completed crater counts on the new C2E mosaic for d > 250 m. We have also calculated kernel density estimates (KDE) for craters larger than 400 m and larger than 2250 Image credit: Daniel C. Berman m. C2E crater density is not well correlated with geologic units defined by [3] in their Low COVERAGE & RESOLUTION: C2E Altitude Mapping Orbit (LAMO; 35 m/px) map. We are investigating the origins of crater coverage is not complete in the Urvara density variations prior to defining new geologic units and age estimates. interior and larger map area. Image resolution also varies significantly across Highest density can be observed on the southern wall / terraces. Two possible causes are: (1) the primary basemap mosaic. We are The terraces are older than the remaining smooth crater floor, and/or (2) secondary craters are producing additional mosaics to guide Image credit: David P. O’Brien responsible for the higher crater density and the terraces have formed simultaneously with the awareness of native image resolution smooth crater interior during the mapping process.

Low density regions correlate with the following features: (1) two unnamed fresh impact craters C2E IMAGE COVERAGE & RESOLUTION: (9.3 km at 38.58S/114.15W; 4.2 km at 46.96S/111.77W); (2) the elongated central ≲ 5 m/px < 10 m/px < 20 m/px peak; (3) the region with the elongated depressions (faults?). These are stratigraphic units that C, BELOW : Detailed view of part of may be distinguished in terms of their crater density (at resolution currently defined by the 5667 Urvara’s northern rim showing rocky craters larger than 250 in diameter). outcrop (top) and talus deposits covering the slope. Note that talus deposits exhibit Within the smooth regions, many subtle depressions can be observed below about 500 m in streaks suggesting multiple cycles of diameter. They could be either some form of pits, thus of endogenic origin, or reworked/heavily mass wasting and separate into discrete degraded older impact craters. However, a more specific statistical analysis is needed to shed lobes at slope base in some places. light on their origin.

C, BELOW: Detailed view of part of Geologic Mapping Approach PRIORITIZED FEATURE TYPES: Urvara’s northern rim, including rocky C outcrops along rim scarp, talus deposits The end goal of our mapping is a chronostratigraphic history of Urvara crater that details new geologic unit boundaries and age Polygons on slope, mapped (red) boulder tracks, estimates for materials in the Urvara interior, allowing us to evaluate the provenance of smooth materials on the southern crater floor. Point Features and large slump block (at right). Note Methodologically, we are taking the approach of performing complete crater counts down to 400 m diameter and mapping a discrete Talus set of surface features, prior to defining units and unit boundaries. Geologic contacts are commonly difficult to define on Ceres, due Mounds (not on LAMO map) also individual boulders on slope and Massifs/Blocks Pit of impact crater floor on terrain at slope base. Detailed view to a pervasive soften or muted character of the surface [3]. A features-first approach allows us to use crater density and feature Spurs Massifs/Blocks of part of Urvara’s northern rim, grouping to inform our choice of unit boundaries, in addition to observed textural changes and superposition relationships. Crater Material Boulders including rocky outcrops along rim scarp, talus deposits on slope, mapped Linear Features (red) boulder tracks, and large slump block (at right). Note also individual A B D Crater Rims boulders on slope and on terrain at Raised rim of large impact crater (10 km and larger) slope base. Raised rim of small impact crater (5-10 km) Degraded impact crater rim Buried impact crater rim C

Other Linear Features High/low albedo streaks Channel Scarp Graben trace Lobate Scarp Groove Ridge Crest Pit Chain Impact Crater Chain Trough or narrow depression

A: There are complex networks of fractures and pit chains in the floor of Urvara crater, which will we map for the first time using the highest resolution data from Dawn’s extended mission (XM2) and compare to the fracture networks in Occator crater also mapped using XM2 data. B: Mounds and domes of various shapes and sizes are found throughout the crater floor. We will differentiate types of mounds (e.g. conical, flat top, etc.) and identify any correlations in locations of mounds and domes and other features in the crater floor. D: Smooth material on the Urvara floor exhibits distinct margins only at some locations.

REFERENCES: [1] Reusch O. et al. (2016) Science, Vol. 353, 6303. [2] Scully J. E. C et al. (2020) Nat. Comm., 11, 3680. [3] Crown D. A. et al. This work was supported by the NASA Discovery Data Analysis Program, grant 80NSSC20K1150. (2018) Icarus, 316, 167-190.