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The Geophysical Environment of (486958) Arrokoth—A Small Kuiper Belt Object Explored by New Horizons

Keane, James T. and Porter, Simon B. and Beyer, Ross A. and Umurhan, Orkan M. and McKinnon, William B. and Moore, Jeffrey M. and Spencer, John R. and Stern, S. Alan and Bierson, Carver J. and Binzel, Richard P. and Hamilton, Douglas P. and Lisse, Carey M. and Mao, Xiaochen and Protopapa, Silvia and Schenk, Paul M. and Showalter, Mark R. and Stansberry, John A. and White, Oliver L. and Verbiscer, Anne J. and Parker, Joel W. and Olkin, Catherine B. and Weaver, Harold A. and Singer, Kelsi N. (2022) The Geophysical Environment of (486958) Arrokoth—A Small Kuiper Belt Object Explored by New Horizons. Journal of Geophysical Research. Planets, 127 (6). Art. No. e2021JE007068. ISSN 2169-9097. doi:10.1029/2021je007068.

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NASA's New Horizons mission performed the first flyby of a small Kuiper Belt Object (KBO), (486958) Arrokoth on 1 January 2019. The fast flyby revealed a fascinating, flattened, contact binary replete with a variety of unexpected geologic terrains. However, the irregular shape and constraints imposed by the fast flyby makes it a challenge to understand these features. Here we use the latest New Horizons shape models of Arrokoth to investigate its geophysical environment, including its surface slopes, gravity field, and moments of inertia—which are critical context for understanding Arrokoth's formation, evolution, and peculiar geology. We find that Arrokoth's surface features have a complicated relationship to its geophysical environment. For example, bright material tends to be concentrated in geopotential lows (like the neck), consistent with mass wasting—however, this trend is not consistently observed across Arrokoth. Mass wasting may naturally explain some aspects of Arrokoth's geology, but the actual dynamics of material transport may be complicated owing to Arrokoth's unique shape, spin-rate, and inferred density. While New Horizons's fast and distant flyby precluded directly measuring Arrokoth's mass, we used techniques previously pioneered for comets and asteroids to infer its density. We find that Arrokoth has a low bulk density of ρ = 235 kg/m3 (1σ range: 155–600 kg/m3). This density is low compared to previously explored small bodies, but is comparable to comets, select binary KBOs, and the ring-moons of Saturn. This low density may be a critical data-point for understanding the formation of planetesimals at the dawn of the Solar System.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemNew Horizons Planetary Data System Small Bodies Node shape model, along with an example MATLAB script for calculating the derived parameters Information
Keane, James T.0000-0002-4803-5793
Porter, Simon B.0000-0003-0333-6055
Beyer, Ross A.0000-0003-4503-3335
Umurhan, Orkan M.0000-0001-5372-4254
McKinnon, William B.0000-0002-4131-6568
Moore, Jeffrey M.0000-0001-5815-0536
Spencer, John R.0000-0003-4452-8109
Stern, S. Alan0000-0001-5018-7537
Bierson, Carver J.0000-0002-6840-7187
Binzel, Richard P.0000-0002-9995-7341
Hamilton, Douglas P.0000-0002-5010-0574
Lisse, Carey M.0000-0002-9548-1526
Mao, Xiaochen0000-0001-7758-9392
Protopapa, Silvia0000-0001-8541-8550
Schenk, Paul M.0000-0003-1316-5667
Showalter, Mark R.0000-0002-8580-4053
White, Oliver L.0000-0003-0126-4625
Verbiscer, Anne J.0000-0002-3323-9304
Parker, Joel W.0000-0002-3672-0603
Olkin, Catherine B.0000-0002-5846-716X
Weaver, Harold A.0000-0003-0951-7762
Singer, Kelsi N.0000-0003-3045-8445
Additional Information:© 2022 The Authors. California Institute of Technology. Government sponsorship acknowledged. This article has been contributed to by US Government employees and their work is in the public domain in the USA. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. Issue Online: 15 June 2022. Version of Record online: 15 June 2022. Accepted manuscript online: 15 May 2022. Manuscript accepted: 13 April 2022. Manuscript revised: 11 April 2022. Manuscript received: 22 September 2021. The authors thank the NASA for support of the New Horizons project, and the authors thank the entire New Horizons team for making the flyby possible. J. T. Keane acknowledges partial support from the Caltech Joint Center for Planetary Astronomy (JCPA) postdoctoral fellowship, and thanks Alan Stern for facilitating his participation in the Arrokoth flyby. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). This research has made use of NASA's Astrophysics Data System. The authors thank David Minton and one anonymous reviewer for their very thorough, insightful, and thought-provoking reviews which resulted in a more compelling manuscript. Data Availability Statement. The stereo and global shape models of Arrokoth are available in McKinnon et al. (2020) and Spencer et al. (2020). The merged shape model of Arrokoth will be formally released as part of a forthcoming New Horizons Planetary Data System Small Bodies Node ( The merged shape model, along with an example MATLAB script for calculating the derived parameters presented in this paper are archived on Zenodo/GitHub:
Funding AgencyGrant Number
Caltech Joint Center for Planetary AstronomyUNSPECIFIED
Subject Keywords:Arrokoth; Kuiper Belt Object; MU69; Geophysics
Issue or Number:6
Record Number:CaltechAUTHORS:20220712-629937000
Persistent URL:
Official Citation:Keane, J. T., Porter, S. B., Beyer, R. A., Umurhan, O. M., McKinnon, W. B., Moore, J. M., et al. (2022). The geophysical environment of (486958) Arrokoth—A small Kuiper Belt Object explored by New Horizons. Journal of Geophysical Research: Planets, 127, e2021JE007068.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115519
Deposited By: George Porter
Deposited On:13 Jul 2022 19:52
Last Modified:13 Jul 2022 19:52

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