The interstellar object 'Oumuamua as a fractal dust aggregate

Eirik G. Flekkøy (1) , Jane Luu (2) , Renaud Toussaint (3, 1)

1 UiO - University of Oslo
2 Institute of Theoretical Astrophysics [Oslo]
3 IPGS - Institut de physique du globe de Strasbourg

The first known interstellar object 'Oumuamua exhibited a nongravitational acceleration that appeared inconsistent with cometary outgassing, leaving radiation pressure as the most likely force. Bar the alien lightsail hypothesis, an ultra-low density due to a fractal structure might also explain the acceleration of 'Oumuamua by radiation pressure (Moro-Martin 2019). In this paper we report a decrease in 'Oumuamua's rotation period based on ground-based observations, and show that this spin-down can be explained by the YORP effect if 'Oumuamua is indeed a fractal body with the ultra-low density of 10 −2 kg m −3. We also investigate the mechanical consequences of 'Oumuamua as a fractal body subjected to rotational and tidal forces, and show that a fractal structure can survive these mechanical forces.

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]; Planétologie et astrophysique de la terre [astro-ph.EP]; Géophysique [physics.geo-ph]

Eirik G. Flekkøy, Jane Luu, Renaud Toussaint. The interstellar object 'Oumuamua as a fractal dust aggregate. The Astrophysical journal letters, 2019, 885 (2), pp.L41. ⟨10.3847/2041-8213/ab4f78⟩. ⟨insu-02366685⟩