The shape and acceleration Omwamwi explained by hydrogen ice in its composition

Scientists have found that the observed properties Omwamwi can explain the high content of ice of the molecular hydrogen in the composition of the asteroid. According to theoretical calculations, the sublimation of the ice is able to further accelerate the object, but the accompanying weight loss — to give it an elongated shape. The article will be submitted to The Astrophysical Journal Letters, its Preprint available at

Omului (1I/’Oumuamua) became the first in the history of observations of macroscopic interstellar object that flew through the Solar system. The opening of the heavenly bodies occurred in October 2017 at Haleakala Observatory in Hawaii. When he saw through the telescope Pan-STARRS, Omwamwi was only 30 million miles from the Earth (five times closer to the Sun).

Initially, astronomers have taken an object behind the comet, but after took him to the class of asteroids. Soon after the discovery, scientists have identified the shape and physical properties of the object: however, according to one estimate, he was dense elongated cigar-shaped body with a length of several hundreds and with a diameter of tens of meters, according to others — of a flattened ellipsoid of the same size. In addition, it was found that on the outgoing trajectory of the asteroid acquired an additional (non-gravitational) acceleration, which could not be reliably explained by sublimation of water ice (similar to known comets in the Solar system).

Darryl Seligman (Darryl Seligman) from the University of Chicago and Gregory Laughlin (Laughlin Gregory) from Yale University theoretically described additional acceleration of the asteroid as a result of sublimation of a certain type of the substance from its surface. As models of the heavenly bodies, the researchers used ellipsoids (like an elongated and flattened), and the calculations used data from the energy that Omwamwi received from the Sun: they are known with high accuracy by determining the trajectory of the object. The authors reviewed nine types of molecular ice and for each of them calculated the proportion of body surface to be coated of the substance to recreate the observed acceleration.

The calculations showed that the smallest fraction of the ice surface requires molecular hydrogen (H2) is a substance able to give the asteroid the observed acceleration as in the case of flattened and elongated shape. Oblate asteroid, according to scientists, could also be coated with molecular nitrogen, neon or argon, in such scenarios, however, requires considerably large proportion of the surface.

For the case of molecular hydrogen, the researchers also considered the loss of mass and concomitant change of form in time. It turned out that at the time of exposure in the Solar system, the greatest transverse dimension of the asteroid could surpass least two to three times, whereas near the Earth due to the loss of substances already six to eight times. The presence of hydrogen ice, so, allowed to explain the unusual geometry of the object it could cause relatively small asymmetries of the body in the stage of formation.

Previously there have been other hypotheses on the nature Omwamwi. So, this year, scientists explained it the shape and acceleration of a specific scenario of formation and shortly after the opening object even tried to find on the asteroid traces of an alien civilization, but later recognized its natural origin.

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