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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| 486958 Arrokoth | 2/8 | https://en.wikipedia.org/wiki/486958_Arrokoth | reference | science, encyclopedia | 2026-05-05T13:09:12.451441+00:00 | kb-cron |
Arrokoth is a contact binary consisting of two hexagonally-shaped lobes attached by a narrow neck or waist, which is encircled by a bright band named Akasa Linea. The lobes were likely once two objects that later merged in a slow collision. The larger lobe, formally named Wenu Lobus, is slightly flattened and measures about 20.1 km (12.5 mi) across its longest axis, while the smaller lobe, Weeyo Lobus, is roughly spherical measures about 15.0 km (9.3 mi) across its longest axis. Based on shape models of Arrokoth constructed from images taken by the New Horizons spacecraft, the dimensions of Wenu are approximately 20.1 km × 19.8 km × 13.7 km (12.5 mi × 12.3 mi × 8.5 mi) while the dimensions of Weeyo are approximately 15.0 km × 14.4 km × 13.6 km (9.3 mi × 8.9 mi × 8.5 mi). Wenu's volume is nearly exactly twice that of Weeyo. As a whole, Arrokoth is 34.5 km (21.4 mi) across its longest axis and is about 13.8 km (8.6 mi) thick. The longest axes of both lobes are nearly aligned with each other and to the rotational axis, which is situated between them. This near-parallel alignment of the lobes suggests that they were mutually locked to each other, likely due to tidal forces, before merging. The alignment of the lobes supports the idea that the two had individually formed from the coalescence of a cloud of icy particles. Prior to the New Horizons flyby of Arrokoth, stellar occultations by Arrokoth had provided evidence for its bilobate shape. The first detailed image of Arrokoth confirmed its double-lobed appearance and was described as a "snowman" by Alan Stern, as the lobes appeared distinctively spherical. In February 2019, one month after the New Horizons flyby, scientists proposed that Arrokoth was extremely flattened, based on New Horizons images of Arrokoth occulting background stars after its closest approach. However, a 2024 reanalysis of New Horizons imagery found that Arrokoth was not as flattened as previously thought.
== Geology ==
=== Spectra and surface ===
Measurements of Arrokoth's absorption spectrum by New Horizons's LEISA spectrometer show that Arrokoth's spectrum exhibits a strong red spectral slope extending from red to infrared wavelengths at 1.2–2.5 μm. Spectral measurements from LEISA revealed the presence of methanol and complex organic compounds on the surface of Arrokoth, but no evidence of water ice. One particular absorption band in Arrokoth's spectrum at 1.8 μm indicates that these organic compounds are sulfur-rich. Given the abundance of methanol on Arrokoth's surface, it is predicted that formaldehyde-based compounds resulting from irradiation should also be present, albeit in the form of complex macromolecules. Arrokoth's spectrum shares similarities with that of 2002 VE95 and the centaur 5145 Pholus, which also display strong red spectral slopes along with signs of methanol present on their surfaces. Preliminary observations by the Hubble Space Telescope in 2016 revealed that Arrokoth has a red coloration, similar to other Kuiper belt objects and centaurs like Pholus. Arrokoth's color is redder than that of Pluto, thus it belongs to the "ultra red" population of cold classical Kuiper belt objects. The red coloration of Arrokoth is caused by the presence of a mix of complex organic compounds called tholins, which are produced from the photolysis of various simple organic and volatile compounds by cosmic rays and ultraviolet solar radiation. The presence of sulfur-rich tholins on Arrokoth's surface implies that volatiles such as methane, ammonia, and hydrogen sulfide were once present on Arrokoth, but were quickly lost due to Arrokoth's small mass. However, less volatile materials such as methanol, acetylene, ethane, and hydrogen cyanide could be retained over a longer period of time, and may likely account for the reddening and production of tholins on Arrokoth. The photoionization of organic compounds and volatiles on Arrokoth was also thought to produce hydrogen gas that would interact with the solar wind, though New Horizons's SWAP and PEPSSI instruments did not detect any signature of solar wind interaction around Arrokoth. From color and spectral measurements of Arrokoth, the surface displays subtle color variation among its surface features. Spectral images of Arrokoth show that the Akasa (neck) region and lineation features appear less red compared to the central region of the smaller lobe Weeyo. The larger lobe Wenu also displays redder regions, informally known as "thumbprints" by the New Horizons team. The thumbprint features are located near Wenu's limb. The surface albedo or reflectivity of Arrokoth varies from 5 percent to 12 percent due to various bright features on its surface. Its overall geometric albedo, the quantity of reflected light in visible spectrum, is measured at 21 percent, typical for most Kuiper belt objects. The overall Bond albedo (the quantity of reflected light of any wavelength) of Arrokoth is measured at 6.3 percent.