Craters on Pluto and Charon Kelsi N. Singer; Paul M. Schenk; Stuart J. Robbins; Veronica J. Bray; William B. McKinnon; Jeffrey M. Moore; John R. Spencer; S A. Stern; W M. Grundy; Carly J. Howett; Cristina M. Dalle Ore; Ross Beyer; Alex H. Parker; Simon B. Porter; Amanda M. Zangari; Leslie A. Young; Hal A. Weaver, Cathy B. Olkin; Kimberly Ennico, Sarah Greenstreet, The New Horizons Geology and Geophysics Team, and The New Horizons Surface Composition Team

Craters! Morphology –transition to central peaks Size-frequency Distributions and Ages Impactor populations 2

Crater Morphology 3

Pluto - Morphology 4 Increasing Diameter Informal Names and Crater Diameters (km)

Pluto – Highest Res 80 m px -1 5 Ejecta Blankets No obvious secondary craters Nested craters (subsurface layering) Youngest craters are darkest 10 km Doublets?

Charon - Morphology Bright rays, dark ejecta, compositional variation, lobate/potentially layered ejecta 6 All scale bars = 30 km All names are informal. RipleyAlice Spock Kirk Dorothy Gale

Central Peaks Visual onset of central peaks at: ~ 8-10 km - Pluto ~ 8 km - Charon 7 Plot Courtesy of Paul Schenk Charon Pluto 50% Central Peaks

Crater Populations 8

Things to keep in mind… What surface are the craters on? –What event are you actually dating? Where do you draw the boundaries of your geologic unit? –affects both counts and surface area What other obscuring factors are involved? –lighting geometry, albedo patterns, etc. What other info helps with age? –Composition, morphology (degradation state)

Pluto Crater Locations 10 Mapped at a consistent resolution of ~900 m/px 1070 craters on encounter hemisphere Cumulative slopes from ~1.8 to All names are informal. SP Cthulhu Mid Lat. Northern Lat. East TR Craters Not Mapped

Pluto – How old is old? SP Indicates a range from ancient to extremely young surfaces R Knee distribution from Greenstreet et al. 2015

Pluto – How young is young? 12 N 2 Ice Infilled, Possibly Convecting -No craters down to ~ 2 km -Age < 10 Ma Sputnik Planum All names are informal. Likely Constructional - Could be 100 Ma - 1 Ga Wright Mons 40 km 150 km

Charon Crater Locations 13 Vulcan Planum All names are informal. Craters Not Mapped Northern Latitudes Mapped at a consistent resolution of ~900 m/px 585 on encounter hemisphere Cumulative slopes from ~1.7 to 2.4

Charon – How old is old? 14 Background plot from Greenstreet et al., 2015 (erratum for Charon plot) Vulcan Planum 30 km Vulcan Planum Northern crater plains 1.All terrains = old!! 2.Not a lot of small craters

Conclusions Range of ages on Pluto  ongoing activity and resurfacing Charon did see early resurfacing (Vulcan Planum), but all observed surfaces likely ~ 4 Ga Measured crater populations do NOT support large numbers of small impactors Knee distribution from Greenstreet et al., 2015 is best match 15

Extras 16

Impactors Scaling: 2 km s -1, gravity regime, cold ice and regolith e.g., Housen and Holsapple, 2011; Holsapple, 1993 Methods as in Singer and Stern, Prediction curves from: Zahnle et al., 2003 Greenstreet et al., 2015 (Table 3) Bierhaus and Dones, 2015 Curves for 4 Ga

Pluto - How old is old? 18 Background plot from Greenstreet et al., 2015 Lines represent different models of the impact flux (colors), and different ages for that density of craters (dashing). Some terrains > 4 Ga Some intermediate Some young No sign of steep slopes or large numbers of small craters

Pluto - How old is old? 19

Scaling Regime Uses the “new” parameters from Housen and Holsapple where they have increased the strength of “cold ice” by an order of magnitude. 20

Pluto – Regional SFDs 21 Cumulative Slopes Consistent with primary crater populations across the Solar System

Charon - SFDs 22 ~30% of Charon’s Surface Area ~10% of Charon’s Surface Area Cumulative Slopes Small craters compromised due to lighting

Greenstreet et al.,

SFDs Pluto: 900 m/px Charon: 900 m/px 24

Pluto - Morphology Potential central pit craters (but could just be degradation) 25

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