Planetary science: How ‘Oumuamua was formed

The interstellar visitor ‘Oumuamua may be a fragment of a planetary body that passed too close to its host star and before being torn apart by tidal forces, suggests a study published in Nature Astronomy . This finding may explain some of the peculiar characteristics of ‘Oumuamua, including its unusually elongated shape, its lack of hazy cometary coma, and that it experienced a non-gravitational force when it flew by the Sun.

‘Oumuamua was the first interstellar object to be detected within the Solar System. It was expected that ‘Oumuamua would be comet-like in appearance, but initial observations found it was an asteroid-like body, with no evidence of cometary activity. ‘Oumuamua also demonstrated a number of unusual features that models have struggled to reproduce.

Yun Zhang and Douglas Lin propose a unified formation theory to explain ‘Oumuamua’s peculiar characteristics. The authors used a state-of-the-art model to simulate the tidal disruption of a parent body orbiting close to its star. They show that if the body comes within a few hundred thousand kilometres of the star, it becomes distorted and then disrupted by stellar tides. The body then produces highly elongated tumbling fragments with enough kinetic energy to escape from the planetary system. The surface of the body becomes very hot and most of the volatile substances evaporate. The authors propose that water can be retained in the deeper layers, and that vaporization through ‘Oumuamua’s porous surface could explain the observed non-gravitational acceleration during its passage by the Sun.

The authors suggest that ‘Oumuamua’s progenitor may have been a kilometre-sized planetesimal (planetary precursor), or a close-in rocky super-Earth, orbiting a low-mass star or a white dwarf.