The shape and acceleration of interstellar asteroid Omwamwi explained by the peculiarities of the origin

Features interstellar asteroid Omului — unusual elongated shape, dry rock and the presence of additional non-gravitational acceleration, — explained in its origin by external tidal destruction of comets or planetesimals. The article, which presents a model of the formation of such objects, published in Nature Astronomy.

Interstellar asteroid 1I/’Oumuamua was opened on 18 October 2017 with network telescopes Pan-STARRS in Hawaii. Initially it was considered an interstellar comet, which received the designation S/2017 U1 (PANSTARRS), but further observations with the VLT telescope at the European southern Observatory showed that the object has no signs of coma is an asteroid. Then comet the index “C” in the name changed to the asteroid, And then gave the object the official name Omului (‘Oumuamua), which translated from Hawaiian can mean “spy” or “messenger from afar”. Data analysis showed that the asteroid has an unusual elongated cigar-shaped form, a top speed of about 26 kilometers per second relative to the Sun, came to us from a point close to the solar apex in the constellation Lyra, moving on open hyperbolic trajectory and will soon leave the Solar system.

Astrophysics Lin, Douglas (Douglas N. C. Lin) from the University of California and Yun Zhang (Yun Zhang) from the National
astronomical observatories of China have developed a model of the formation of interstellar objects similar to Omwamwi. According to their calculations, the parent bodies for such objects can be long-period comets from the Oort cloud, a small main sequence stars or white dwarfs, or residual planetesimals rich in volatile substances and orbiting such stars. The size of the parent bodies in this case is about a kilometer.

In the approaches of comets or planetesimals with the parent star at a distance that is less than 6×108m, of the body speed up, greatly deformed and then destroyed by tidal forces of the star, producing a large number of strongly elongated fragments. Such fragments can leave their star system and not be captured by planets like Jupiter. In this case the surface of the bodies composed of ice and rocks that are intensely heated during the rapprochement with the star, which leads to the melting of silicates and the formation of a dry crust and “transformation” of cometary objects in the asteroid. At a depth of up to 3 meters under the surface of the resulting fragments, the temperature can be maintained at 28 Kelvin, which is sufficient for sublimation of carbon monoxide. At the same time, water and carbon dioxide, whose sublimation temperature is higher, remain in condensed form, and at depths of 0.1-0.2 and 0.2-0.5 meters, respectively. The evaporation of these volatile substances explains additional non-gravitational acceleration Omwamwi during its passage through the inner Solar system.

The study authors noted that the estimated
asteroid number densities of interstellar objects (a 3.5×1013- 2×1015pieces
cubic parsec) is a thousand times more numerical density of cometary interstellar
objects in the Oort cloud. Because the spans of these bodies pass through the habitable zone of stars, we cannot discard the prospect of panspermia — the hypothesis of the emergence of life on Earth as a result of inclusion of microorganisms by meteorites from outer space, scientists say.

Earlier, a team of researchers from the Institute of astronomy, max Planck Society reported about the four most interesting candidates for the role of the parent stellar system Omului — all of them are dwarf stars. And their colleagues from Harvard University have described a new method of search of interstellar objects, like asteroid or comet Omwamwi 2I/Borisov, based on the observation of short eclipses of stars — coatings.

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