Photometry of Kuiper belt object (486958) Arrokoth from New Horizons LORRI

Abstract

On January 1st 2019, the New Horizons spacecraft flew by the classical Kuiper belt object (486958) Arrokoth (provisionally designated 2014 MU69), possibly the most primitive object ever explored by a spacecraft. The I/F of Arrokoth is analyzed and fit with a photometric function that is a linear combination of the Lommel-Seeliger (lunar) and Lambert photometric functions. Arrokoth has a geometric albedo of = 0.21 −0.04 +0.05 at a wavelength of 550 nm and  0.24 at 610 nm. Arrokoth's geometric albedo is greater than the median but consistent with a distribution of cold classical Kuiper belt objects whose geometric albedos were determined by fitting a thermal model to radiometric observations. Thus, Arrokoth's geometric albedo adds to the orbital and spectral evidence that it is a cold classical Kuiper belt object. Maps of the normal reflectance and hemispherical albedo of Arrokoth are presented. The normal reflectance of Arrokoth's surface varies with location, ranging from  0.10 -0.40 at 610 nm with an approximately Gaussian distribution. Both Arrokoth's extrema dark and extrema bright surfaces are correlated totopographic depressions. Arrokoth has a bilobate shape and the two lobes have similar normal reflectance distributions: both are approximately Gaussian, peak at  0.25 at 610 nm, and range from  0.10 -0.40, which is consistent with co-formation and co-evolution of the two lobes. The hemispherical albedo of Arrokoth varies substantially with both incidence angle and location, the average hemispherical albedo at 610 nm is 0.063  0.015. The Bond albedo of Arrokoth at 610 nm is 0.062  0.015.

High Resolution Search for KBO Binaries from New Horizons

“…For the CC KBOs, we use the average geometric albedo derived from Herschel observatory observations of CCs (Vilenius et al 2014). We note that the reported geometric albedo of CC Arrokoth is 0.21 −0.04 +0.05 (Hofgartner et al 2021), which is slightly larger than, but consistent within the error bars, the average CC value. The approximate effective diameters (d N ) are derived from the listed H 0 values and geometric albedos.…”

High-resolution Search for Kuiper Belt Object Binaries from New Horizons

“…For the CC KBOs, we use the average geometric albedo derived from Herschel observatory observations of CCs (Vilenius et al 2014). We note that the reported geometric albedo of CC Arrokoth is -+ 0.21 0.04 0.05 (Hofgartner et al 2021), which is slightly larger than the average CC value, although consistent within the error bars. The approximate effective diameters (d N ) are derived from the listed H 0 values and geometric albedos.…”

The sublimative evolution of (486958) Arrokoth

“…where P X is the dynamic sublimation pressure exerted by the escaping gases on the surface, 𝐶 X is an empirical factor analogous to YORP coefficients, 𝜌 is the bulk density of Arrokoth; 𝑅 is the mean radius of Arrokoth, approximately 8.5 km (Stern et al 2019), Φ "\] is the sublimative gas flux from the surface, 𝑚 is the molecular mass of the volatile, and 𝑣 E`abBcd is the mean molecular thermal velocity of the molecule. This model assumes that the object has a very low albedo (consistent with the 6.3% bond albedo of Arrokoth [Hofgartner et al 2020]), and is composed entirely of a single volatile ice (for example, CO). This model also assumes that the multiple different chemical species composing Arrokoth do not interact with one another.…”