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

• Published in: Journal of geophysical research. Planets 2022-06, Vol.127 (6), p.n/a
• Main Authors: Keane, James T., Porter, Simon B., Beyer, Ross A., Umurhan, Orkan M., McKinnon, William B., Moore, Jeffrey M., Spencer, John R., Stern, S. Alan, Bierson, Carver J., Binzel, Richard P., Hamilton, Douglas P., Lisse, Carey M., Mao, Xiaochen, Protopapa, Silvia, Schenk, Paul M., Showalter, Mark R., Stansberry, John A., White, Oliver L., Verbiscer, Anne J., Parker, Joel W., Olkin, Catherine B., Weaver, Harold A., Singer, Kelsi N.
• Format: Article
• Language: English
• Subjects: Arrokoth; Asteroids; Bulk density; Comets; Evolution; Flyby missions; Geology; Geophysics; Geopotential; Gravitational fields; Icy satellites; Kuiper belt; Kuiper Belt Object; Mass wasting; Moments of inertia; Moon; MU69; New Horizons mission; Outer solar system; Planet formation; Pluto; Saturn; Saturn rings; Saturn satellites; Solar system; Space missions; Spacecraft; Trans-Neptunian objects; Voyager 1 spacecraft
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2021JE007068

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. Plain Language Summary NASA's New Horizons mission performed the first flyby of a small Kuiper Belt Object (KBO), (486958) Arrokoth on 1 January 2019. Arrokoth is a ∼30‐km long, peanut shaped, icy body in the Kuiper Belt—a reservoir of small bodies left over from the Solar System's formation. Arrokoth is the most distant, and likely the least evolved object, ever explored by a spacecraft. Arrokoth's unusual shape makes it challenging to determine how material moves across its surface. We use the latest shape models to calculate Arrokoth's gravity field. Bright material tends to collect in Arrokoth's lowest locations, perhaps indicating material can move downslope. While New Horizons was not able to measure the density of Arrokoth, we are able to infer it using techniques pioneered for studying asteroids and com