Some New Results and Perspectives Regarding the Kuiper Belt Object Arrokoth’s Remarkable, Bright Neck

Stern, S. A.; Keeney, Brian A.; Singer, K. N.; White, O. L.; Hofgartner, Jason D.; Grundy, W. M.

doi:10.3847/psj/abee26

Cited by 10 publications

(10 citation statements)

References 23 publications

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“…Another set with f = 1.00-1.25 for Nix/Hydra and f = 1.5-4.75 for Styx/ Kerberos will yield better estimates of the masses for Styx and Kerberos. Choosing among possible volume estimates requires more detailed shape models, as in studies of Arrokoth (e.g., McKinnon et al 2020;Spencer et al 2020;Stern et al 2021). Together, these modeling efforts will enable a clearer picture of the origin and early evolution of the Pluto-Charon satellite system.…”

Section: Discussionmentioning

confidence: 99%

A Pluto–Charon Sonata IV. Improved Constraints on the Dynamical Behavior and Masses of the Small Satellites

Kenyon

Bromley

2022

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We discuss a new set of ∼500 numerical n-body calculations designed to constrain the masses and bulk densities of Styx, Nix, Kerberos, and Hydra. Comparisons of different techniques for deriving the semimajor axis and eccentricity of the four satellites favor methods relying on the theory of Lee & Peale, where satellite orbits are derived in the context of the restricted three-body problem (Pluto, Charon, and one massless satellite). In each simulation, we adopt the nominal satellite masses derived in Kenyon & Bromley, multiply the mass of at least one satellite by a numerical factor f ≥ 1, and establish whether the system ejects at least one satellite on a timescale ≤4.5 Gyr. When the total system mass is large (f ≫ 1), ejections of Kerberos are more common. Systems with lower satellite masses (f ≈ 1) usually eject Styx. In these calculations, Styx often “signals” an ejection by moving to higher orbital inclination long before ejection; Kerberos rarely signals in a useful way. The n-body results suggest that Styx and Kerberos are more likely to have bulk densities comparable with water ice, ρ SK ≲ 2 g cm−3, than with rock. A strong upper limit on the total system mass, M SNKH ≲ 9.5 × 1019 g, also places robust constraints on the average bulk density of the four satellites, ρ SNKH ≲ 1.4 g cm−3. These limits support models where the satellites grow out of icy material ejected during a major impact on Pluto or Charon.

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Section: Discussionmentioning

confidence: 99%

A Pluto–Charon Sonata IV. Improved Constraints on the Dynamical Behavior and Masses of the Small Satellites

Kenyon

Bromley

2022

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“…As shown in Figure 14, the neck (L1) and bright materials within Sky (L2) correspond to geopotential lows (Spencer et al., 2020; Stern et al., 2019, 2021). The brightest material on Arrokoth is within its neck (Hofgartner et al., 2021; Stern et al., 2021), which corresponds to some of the lowest geopotentials on Arrokoth. However, not all bright materials are located in geopotential lows.…”

Section: Implications For Arrokoth's Geologymentioning

confidence: 95%

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

et al. 2022

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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.

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“…The polar regions actually receive about twice as much insolation as the equator zone (Umurhan et al 2022). The higher albedo neck region (Stern et al 2021) receives less energy than the equatorial zone owing to shadowing effects, but this is partially offset by thermal radiation from surfaces in the neckʼs environment. For the epoch of the New Horizons flyby (subsolar latitude ≈−61.9°), the model yields peak daytime temperatures near the pole ranging from 50 to 60 K, 30-40 K near the equator, and 10-15 K in the polar night.…”

Section: Constraints On Thermal Models For Arrokothmentioning

confidence: 99%

Detection of Radio Thermal Emission from the Kuiper Belt Object (486958) Arrokoth during the New Horizons Encounter

et al. 2022

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The New Horizons spacecraft encountered the Kuiper Belt object (KBO) Arrokoth (486958), originally designated as 2014 MU69 and formerly called “Ultima Thule,” on 2019 January 01. At 43.3 au from the Sun and 44.4 au from Earth, this was the most distant spacecraft reconnaissance of a solar system body to date. The Radio Science Experiment (REX) on New Horizons performed radiometry measurements of the KBO's thermal emission at λ = 4.2 cm in two observation slots, one before (dayside) and one after (nightside) the point of closest approach. Owing to the small size of the target, the intensity of the thermal emission was expected to be only marginally detectable. The KBO was not detected on approach because of unexpectedly large variations in the REX system temperature. A brightness temperature T b = 29 ± 5 K was derived for the nightside observation, considerably less than the predicted equilibrium temperature of ∼50 K derived for Arrokoth on the dayside. A model explaining this day−night contrast is used to constrain the global values of emissivity, thermal inertia, and electrical skin depth of the KBO. In particular, models with small values of thermal inertia and small values of electrical skin depth are excluded. Relatively high values of the effective radio emissivity (E eff > 0.8) provide better agreement with the REX observation.

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Some New Results and Perspectives Regarding the Kuiper Belt Object Arrokoth’s Remarkable, Bright Neck

Cited by 10 publications

References 23 publications

A Pluto–Charon Sonata IV. Improved Constraints on the Dynamical Behavior and Masses of the Small Satellites

A Pluto–Charon Sonata IV. Improved Constraints on the Dynamical Behavior and Masses of the Small Satellites

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

Detection of Radio Thermal Emission from the Kuiper Belt Object (486958) Arrokoth during the New Horizons Encounter

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