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تسجيل مستخدم جديدSublimation as an effective mechanism for flattened lobes of (486958) Arrokoth
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The New Horizons spacecrafts flyby of Kuiper Belt Object (KBO) (486958) Arrokoth revealed a bilobed shape with highly flattened lobes both aligned to its equatorial plane, and a rotational axis almost aligned to the orbital plane (obliquity ~99 deg). Arrokoth belongs to the Cold Classical Kuiper Belt Object population that occupies dynamically undisturbed orbits around the Sun, and as such, is a primitive object that formed in situ. Therefore, whether its shape is primordial or evolutionary carries important implications for understanding the evolution of both KBOs and potentially their dynamically derived objects, Centaurs and Jupiter Family Comets (JFC). Applying our mass loss driven shape evolution model (MONET), here we suggest that the current shape of Arrokoth could be of evolutionary origin due to volatile outgassing in a timescale of about 1 to 100 Myr, while its spin state would not significantly affected. We further argue that such a process may be ubiquitous in the evolution of the shape of KBOs shortly after their formation. This shape changing process could also be reactivated when KBOs dynamically evolve to become Centaurs and then JFCs and receive dramatically increased solar heating.
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The New Horizons space probe led the first close flyby of one of the most primordial and distant objects left over from the formation of the solar system, the contact binary Kuiper Belt object (486958) Arrokoth, which is composed of two progenitors,
the lobes nicknamed Ultima and Thule. In the current work, we investigated Arrokoths surface in detail to identify the location of equilibrium points and also explore each lobes individual dynamic features. We assume Arrokoths irregular shape as a homogeneous polyhedra contact binary. We numerically explore its dynamic characteristics by computing its irregular binary geopotential to study its quantities, such as geometric height, oblateness, ellipticity, and zero-power curves. The stability of Arrokoth Hill was also explored through zero-velocity curves. Arrokoths external equilibrium points have no radial symmetry due to its highly irregular shape. We identified even equilibrium points concerning its shape and spin rate: i.e., four unstable external equilibrium points and three inner equilibrium points, where two points are linearly stable, with an unstable central point that has a slight offset from its centroid. Moreover, the large and small lobes each have five equilibrium points with different topological structures from those found in Arrokoth. Our results also indicate that the equatorial region of Arrokoths lobes is an unstable area due to the high rotation period, while its polar locations are stable resting sites for surface particles. Finally, the zero-power curves indicate the locations around Arrokoth where massless particles experience enhancing and receding orbital energy.
We consider the history of New Horizons target (486958) Arrokoth in the context of its sublimative evolution. Shortly after the Suns protoplanetary disk (PPD) cleared, the newly intense sunlight sparked a sublimative period in Arrokoths early history
that lasted for ~10-100 Myr. Although this sublimation was too weak to significantly alter Arrokoths spin state, it could drive mass transport around the surface significant enough to erase topographic features on length scales of ~10-100 m. This includes craters up to ~50-500 m in diameter, which suggests that the majority of Arrokoths craters may not be primordial (dating from the merger of Arrokoths lobes), but rather could date from after the end of this sublimative period. Thereafter, Arrokoth entered a Quiescent Period (which lasts to the present day), in which volatile production rates are at least 13 orders of magnitude less than the ~10^24 molecules/s detection limit of the New Horizons spacecraft (Lisse et al. 2020). This is insufficient to drive either mass transport or sublimative torques. These results suggest that the observed surface of Arrokoth is not primordial, but rather dates from the Quiescent Period. By contrast, the inability of sublimative torques to meaningfully alter Arrokoths rotation state suggests that its shape is indeed primordial, and its observed rotation is representative of its spin state after formation.
We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other d
ebris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by SOFIA with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 Aug 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 $pm$ 0.0005 hours. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the New Horizons flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies.
The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, are primitive objects preserving information about Solar System formation. The New Horizons spacecraft flew past one of these objects, the 36 km long contac
t binary (486958) Arrokoth (2014 MU69), in January 2019. Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters diameter) within a radius of 8000 km, and has a lightly-cratered smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.
The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU$_{69}$) has been largely undisturbed since its formation. We study its surface composition using data collected by the New Horizons spacecraft. Methanol ice is present a
long with organic material, which may have formed through radiation of simple molecules. Water ice was not detected. This composition indicates hydrogenation of carbon monoxide-rich ice and/ or energetic processing of methane condensed on water ice grains in the cold, outer edge of the early Solar System. There are only small regional variations in color and spectra across the surface, suggesting Arrokoth formed from a homogeneous or well-mixed reservoir of solids. Microwave thermal emission from the winter night side is consistent with a mean brightness temperature of 29$pm$5 K.
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