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A 2000-2017 set of long-period comets with high-quality orbits of perihelion distance <1 AU is used to show that the objects that perish shortly before perihelion are nearly exclusively the Oort Cloud comets, especially those with perihelia within 0.6 AU of the Sun, intrinsically fainter, and dust poor. Their propensity for disintegration is much higher than predicted by Bortles perihelion survival rule, prompting the author to propose a new synoptic index to be tested in future prognostication efforts. By their susceptibility to demise near the Sun, the nuclei of Oort Cloud comets differ dramatically from the nuclei of other long-period comets that almost always survive. In this scenario, `Oumuamua -- discovered after perihelion -- is in all probability a major piece of debris of an interstellar comet that was bound to perish near perihelion if it was similar to, though much fainter than, the known Oort Cloud comets. The nondetection of `Oumuamua by the Spitzer Space Telescope is compatible with optical data for pancake shape, but not for cigar shape, with the maximum dimension not exceeding 160 m (at an 0.1 albedo). Although the solar radiation pressure induced nongravitational acceleration requires very high porosity, `Oumuamuas estimated mass is orders of magnitude greater than for a cloud of unbound submicron-sized dust grains of equal cross section. The acceleration could have displaced `Oumuamua by 250,000 km in 50 days, scattering other potential debris over a large volume of space.
We perform $N$-body simulations of the early phases of open cluster evolution including a large population of planetesimals, initially arranged in Kuiper-belt like discs around each star. Using a new, 4th-order and time-reversible $N$-body code on Gr
The interstellar comet 2I/Borisov bears a strong resemblance to Oort Cloud comets, judging from its appearance in images taken over the first six weeks of observation. To test the proposed affinity in more diagnostic terms, 2I is compared to Oort Clo
The discovery of 1I/2017 U1 (Oumuamua) has provided the first glimpse of a planetesimal born in another planetary system. This interloper exhibits a variable colour within a range that is broadly consistent with local small bodies such as the P/D typ
Comets in the Oort cloud evolve under the influence of internal and external perturbations, such as giant planets, stellar passages, and the galactic tidal field. We aim to study the dynamical evolution of the comets in the Oort cloud, accounting for
We have conducted a search for radio emission consistent with an artificial source targeting 1I/Oumuamua with the Robert C. Byrd Green Bank Telescope (GBT) between 1.1 and 11.6 GHz. We searched the data for narrowband signals and found none. Given th