Scientists explain anomalies in the orbit of the first interstellar visitor

oumuamua recreation

Mankind has created networks of telescopes and observatories that scan the sky during the night and day at all wavelengths. On October 19, 2017 astronomer Robert Weryk, with Pan-STARRS imaging in Hawaii, found an oddly long object in a hyperbolic orbit. Its trajectory showed an origin from the stars and that it was performing a brief flyby in our solar system, making it the first confirmed interstellar visitor.

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Digital illustration of what Oumuamua may look like, its elongated shape was confirmed by different measurements.


In astronomy, when an object is found in space, the first thing you want to do is to know its past and future trajectory. For this, it is necessary to place it in several instants of time. When their theoretical trajectory was studied against the measured positions, a discordance was found caused by an acceleration different from that of the gravity of the Sun and the planets.

Comets are usually icy objects that undergo sublimation processes due to the heat of the Sun during their passage through perihelion. The gases that are released, by Newton's third law, cause an acceleration on the comet. Oumuamua was believed to be undergoing a similar phenomenon, however, experimental measurements did not favor this explanation and strong inconsistencies with current models appeared.

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Simulation showing the trajectory of Oumuamua over time compared to the inner planets.

Trapped hydrogen

Exhaustive observations of the interstellar traveler showed an absence of a cometary tail. The new study by the team led by Jennifer B. Bergner proposes that it was originally a plantesimal composed of ice and that it was triggered during the formation of its star system. Its entire evolution would have been subject to the perturbations of the interstellar medium.

The highly charged particles impacting with Oumuamua broke up the ice molecules, which is an incredibly efficient form of H2 production. The released hydrogen was trapped in the matrix, finally escaping in its passage through the solar system. This explanation better satisfies the observations. It should be noted that this same diatomic hydrogen could not be detected by the optical and infrared spectrography that was performed.

Although computational models of heat flow and H2 production over Oumuamua offer a very close approximation to the data obtained, certain limitations remain. The first of these is a better approximation of the mixing of elements present and the proliferation of gases at different temperature ranges in the various ice thicknesses.

The biggest problem is the upper limit of micrometer particles in the object, since some have been detected with sizes greater than 100 micrometers. This has only been evidenced in large comets in the solar system.

This same study opens the door to a better understanding of the behavior of objects in the Oort cloud and their effects due to the lack of heliospheric protection. It also shows that smaller comets should show non-gravitational accelerations similar to those of Oumuamua. More studies are still needed to properly understand the functioning of these marvelous objects.

Francisco Andrés Forero Daza