‘Oumuamua: A Possible Fragment of a Pluto-Like Exoplanet

Credit: William Hartmann/AP.

‘Oumuamua was discovered on October 19, 2017 by the Pan-STARRS telescope in Hawaii and was recognized to be the first interstellar object discovered within our solar system based on its hyperbolic orbit. Various speculations were made as to its origin. It was initially thought to be a rogue comet from outside of our solar system; however, ‘Oumuamua did not develop a coma during its close approach to the Sun like most solar system comets do. Therefore, some scientists suggested that ‘Oumuamua was instead a rogue asteroid-like object. Some scientists have even invoked alien technology as the only way to explain ‘Oumuamua’s intriguing properties.

Two recent studies by Alan Jackson and Steve Desch from Arizona State University suggest that ‘Oumuamua is primarily made up of nitrogen ice and is a shard from a Pluto-like exoplanet in another solar system. As ‘Oumuamua passed by the Sun, it exhibited a non-gravitational acceleration, meaning that its trajectory could not be described by gravity alone. This boost in speed could be explained by ices evaporating from the surface of the object due to heating from the Sun. The research of Jackson and Desch explored multiple compositions of ices such as H2, H2O, CO2, N2, NH3, O2, CO, and CH4, and calculated the non-gravitational acceleration that could be caused by evaporation of these ices providing thrust to ‘Oumuamua. They concluded that evaporation of N2 ice best satisfies the observed boost in speed (and other observational constraints) if ‘Oumuamua has an albedo similar to Pluto. Pluto was the primary target of NASA’s New Horizons mission that extensively characterized its geology and chemical composition during its flyby in 2015 and discovered that N2 ice essentially covers its entire surface. Similar nitrogen ice layers are also observed on Triton, the largest moon of Neptune.  Jackson and Desch conclude that ‘Oumuamua was ejected from its home system some 400 million years ago as a fragment of a Pluto-like object. It then survived cosmic-ray bombardment during its trek through interstellar space to make its flyby of the Sun in 2017, where nitrogen evaporation caused extreme mass loss and its curious observed properties. Studies of interstellar objects currently suffer from small number statistics, but the sensitivity of ground-based optical surveys and the advent of the Vera C. Rubin Observatory are expected to raise their discovery rate to about one per year and improve our understanding of these fascinating objects. READ MORE