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The Interstellar Object ’Oumuamua as a Fractal Dust Aggregate
Résumé
The first known interstellar object ’Oumuamua exhibited a nongravitational acceleration that appeared inconsistentwith cometary outgassing, leaving radiation pressure as the most likely force. Barring the alien lightsail hypothesis,
an ultra-low density due to a fractal structure might also explain the acceleration of ’Oumuamua by radiation
pressure. [voir la suite] In this Letter 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 0.01 kg/m3. 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.