The Inner Kernel of the Classical Kuiper Belt

Abstract The “kernel” of the classical Kuiper Belt was discovered by Petit et al. as a visual overdensity of objects with low ecliptic inclinations and eccentricities at semimajor axes near ∼44 au. This raises the question—are there other structures present in the classical Kuiper Belt? If there are, clustering algorithms applied to orbits transformed into free elements may yield the best chance of discovery. Here, we derive barycentric free orbital elements for objects in the classical Kuiper Belt, and use the Density-Based Spatial Clustering of Applications with Noise algorithm to identify a new structure, which we dub the inner kernel, located at a ∼ 43 au just inward of the kernel ( a ∼ 44 au), which we also recover. It is as yet unclear whether the inner kernel is an extension of the kernel or a distinct structure. Forthcoming observations, including those by the Vera C. Rubin Observatory’s Legacy Survey of Space and Time may provide further evidence for the existence of this structure, and perhaps resolve the question of whether there are two distinct structures.