51st Lunar and Planetary Science Conference (2020) 1212.pdf

PROGRESS ON GLOBAL GEOLOGICAL MAPPING OF . O. L. White1,2, K. N. Singer3, D. A. Wil- liams4, J. M. Moore2, R. M. C. Lopes5, S. A. Stern3, P. J. McGovern6. 1SETI Institute, Mountain View, CA, 94043 ([email protected]), 2NASA Ames Research Center, Moffett Field, CA, 94035, 3Southwest Research Institute, Boul- der, CO, 80302, 4Arizona State University, Tempe, AZ, 85281, 5NASA Jet Propulsion Laboratory, Caltech, Pasade- na, CA, 91109, 6Lunar and Planetary Institute, Houston, TX, 77058.

Introduction: Following its flyby of the Pluto sys- bladed terrain deposits, a sequence that suggests an tem in 2015, NASA’s spacecraft re- altitudinal control on ice stability [9]. The Tartarus turned high quality images revealing an unexpectedly Dorsa map reveals evidence for recession of the bladed diverse range of terrains on Pluto [1,2]. Pluto’s ter- terrain deposits in response to climate change, exhum- rains exhibit highly disparate morphologies and crater ing what may be a precursor to these deposits in the spatial densities [3,4], implying a complex geological form of arcuate terrain [9]. The bright, pitted uplands history. Surface renewal is ongoing, as demonstrated appear to be where both arcuate terrain and bladed most compellingly by the ice of Sput- terrain deposits are experiencing deposition of a thin nik Planitia [5,6]. Pluto’s geology displays evidence veneer of volatile ices (mainly nitrogen) from Pluto’s for having been affected by both endogenic and ex- atmosphere, some of which is returned to Sputnik ogenic energy sources, and its complex nature is likely Planitia via glacial flow. The map also shows the per- caused by combinations of these influences governing vasiveness of surface collapse within the uplands to the the distribution and behavior of different surface com- east of , in the form of pits reaching positional suites to strongly varying degrees across many km across and >1 km deep. These pits common- even small lateral distances. ly form complexes that are often organized into NW- We are using established planetary geologic map- SE-aligned linear chains along structural trends that ping techniques [7] to produce a global US Geological can reach >200 km long, and which likely represent Survey Scientific Investigations Map (SIM) at 1:7M grabens, meaning that tectonism is at least partly re- scale for the >75% of Pluto’s surface that was imaged sponsible for the surface collapse seen here. by New Horizons. This map will represent a critical tool for resolving differing hypotheses of Pluto’s evo- lution. This abstract presents a summary of the map- ping that has been performed to date, which consists of separate maps created for various projects investigat- ing different aspects of Pluto’s geology, the line work of which will be imported into the final SIM. Near side geological mapping: Published map- ping of Pluto’s near side (covered by imaging ranging from 76 to 890 m/pixel) includes a geological map of Sputnik Planitia and East [8], as well as mapping of the ice bladed terrain deposits of Tartarus Dorsa [9], with an updated version of the latter map having been produced at a scale of 1:7M (Fig. 1) [10]. The Sputnik Planitia map demonstrates how this immense deposit of nitrogen ice variably re- sponds to both endogenic and exogenic environmental influences across its expanse, specifically radiogenic heat production powering in thicker por- tions of the nitrogen ice, and Pluto’s seasonal and Milankovitch cycles, as well as local topographic and atmospheric effects, governing the balance of sublima-

tion and deposition of nitrogen ice across it. Figure 1. Geological map of the nitrogen ice plains of Taken together, these maps reveal how the chang- eastern Sputnik Planitia (SP), bright, pitted uplands of ing terrains from Sputnik Planitia to the pitted uplands East Tombaugh Regio (ETR), bladed terrain deposits of East Tombaugh Regio to Tartarus Dorsa manifest a of Tartarus Dorsa (TD), eroded, smooth uplands of surficial composition sequence from dominance by southern Hayabusa Terra (HT), and dark, eroded up- nitrogen closest to Sputnik Planitia to increasing domi- lands of Krun Macula (KM) [10]. nance of methane ice to the east culminating in the 51st Lunar and Planetary Science Conference (2020) 1212.pdf

Tectonics mapping: Structural mapping has been tions [9] and elevated terrain in far side limb profiles. completed for Pluto’s near side (Fig. 2) [11]. Pluto The low , far side maculae (unit mdt) display a possesses a non-random system of extensional faults complex spatial relationship with the bladed terrain that include normal fault scarps and graben, sharp- deposits, with both units embaying occurrences of the crested ridges, troughs, and pit chains. The ubiqui- other. These two units may be genetically related, tousness of extensional faulting indicates that partial whereby suppression of mobilization of surface me- freezing of a subsurface is the overarching driv- thane ice (via sublimation and deposition) for portions er of tectonism on Pluto, with localized effects govern- of the deposits in response to climate change would ing the nature and timing of how the expansion is ex- allow dark haze particles settling from the atmosphere pressed tectonically. Mapped tectonics have been as- to accumulate as a continuous layer onto the deposits signed into discrete systems, including those to the and form maculae [13], as has happened for the inert west of Sputnik Planitia that are quasi-radial (orange) water ice crust of Macula (unit sp). Alterna- and radial (yellow) to Sputnik Planitia, and are the tively, the maculae may represent areas where the most prominent and well-preserved tectonism on the bladed terrain deposits have receded in response to near side; those to the east of Sputnik Planitia (red) such secular climate change, revealing a dark substrate. that display a consistent NW-SE orientation, and Simonelli is the only identified on the far which form great circles with the northern fractures side (unit ic), the floor of which displays the eastern- west of Sputnik Planitia, with which they may form a most nitrogen ice deposits that can be identified on the single tectonic system; those at the western and eastern far side (unit bp). Tectonism has not been conclusive- edges of the near side (green) that are oriented azi- ly identified on the far side, but a network of low albe- muthally to Sputnik Planitia, and which are more poor- do, low elevation lineations observed between 330°E ly-preserved than the Sputnik quasi-radial and radial and 30°E (unit dd) may represent fractures. fractures; and a NNE-SSW-aligned, eroded, fragmen- tary band of troughs, ridges, elevated and elongate depressions that extends across almost the entire near side (purple), and which is likely the earli- est tectonic system yet seen on Pluto.

Figure 3. Geological map of Pluto’s far side [12]. Acknowledgements: This research has been fund- Figure 2. Mapped tectonism on Pluto’s near side [11]. ed by NASA’s PDART and NFDAP programs. Far side geological mapping: A geological map of References: [1] Stern S. A. et al. (2018) Annu. Pluto’s far side (Fig. 3) has been produced for this Rev. Astron. Astrophys., 56, 357-392. [2] Moore J. M. hitherto relatively unstudied area [12]. The pixel scale et al. (2016) Science, 351, aad7055. [3] Robbins S. J. of the low-phase imaging that covers the far side rang- et al. (2017) Icarus, 287, 187-206. [4] Singer K. N. et es from 2.2 km/pixel at its western edge to 40.6 al. (2019) Science, 363, 955-959. [5] Trowbridge A. J. km/pixel at the eastern edge, meaning that only surface et al. (2016) Nature, 534, 79-81. [6] McKinnon W. B. features on a scale larger than ~10 km and ~200 km et al. (2016) Nature, 534, 82-85. [7] Skinner J. A. et al. are resolved at the respective ends, and units are de- (2018) Planetary Geologic Mapping Protocol-2018. fined primarily by their albedo. Near side imaging that USGS, Flagstaff, AZ. [8] White O. L. et al. (2017) abuts the far side is an important anchor for far side Icarus, 287, 261-286. [9] Moore J. M. et al. (2018) mapping, as unit contacts and large-scale structures Icarus, 300, 129-144. [10] Moore J. M. and A. D. that are easily defined in high resolution near side cov- Howard (2020) “Climate History of Pluto as Revealed erage can be extrapolated into the far side. by its Landscapes”, Pluto System After New Horizons, The far side geological map reveals that Tartarus University of Arizona Press, submitted. [11] McGov- Dorsa form the western end of a vast, low-latitude belt ern P. J. et al. (2019) Pluto System After New Hori- of high elevation bladed terrain deposits (unit btd) ex- zons, Abstract #7063. [12] Stern S.A. et al. (2020) tending across >220° of longitude, as indicated by a “The Far Side of Pluto”, Icarus, submitted. [13] Grun- strong methane signature in IR spectroscopy observa- dy W. M. et al. (2018) Icarus, 314, 232-245.