Shmuel Bialy, Abraham Loeb
2018 · arXiv
`Oumuamua (1I/2017 U1) is the first object of interstellar origin observed in the Solar System. Recently, \citet{Micheli2018} reported that `Oumuamua showed deviations from a Keplerian orbit at a high statistical significance. The observed trajectory is best explained by an excess radial acceleration $Δa \propto r^{-2}$, where $r$ is the distance of `Oumuamua from the Sun. Such an acceleration is naturally expected for comets, driven by the evaporating material. However, recent observational and theoretical studies imply that `Oumuamua is not an active comet. We explore the possibility that the excess acceleration results from Solar radiation pressure. The required mass-to-area ratio is $(m/A)\approx 0.1$ g cm$^{-2}$. For a thin sheet this requires a thickness of $\approx 0.3-0.9$ mm. We find that although extremely thin, such an object would survive an interstellar travel over Galactic distances of $\sim 5$ kpc, withstanding collisions with gas and dust-grains as well as stresses from rotation and tidal forces. We discuss the possible origins of such an object. Our general results apply to any light probes designed for interstellar travel.
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This author has also proposed that the solar system has already been visited: "‘Oumuamua may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization."[0] The rest of the paper covers the possibility that the ‘Oumuamua object was sent unintentionally to Earth vicinity by an alien civilization. [0] https://arxiv.org/pdf/1810.11490.pdf
Comets show similar "weird" accelerations. Its not aliens, its probably just outgassing! Here's the first public paper I could find off hand on the topic. The acceleration due to outgassing of 67P/Churyumov–Gerasimenko (of Rosetta spacecraft fame) https://arxiv.org/abs/1902.02701 While I haven't personally seen anything that decides if Oumuamua counts as a comet or not, thats beside the point, since anything can outgas with enough heat. It appears to be covered with Tholins (based on the spectroscopy https://arxiv.org/abs/1712.06552) which aren't immune to outgassing, and likely make up at least part of the "anomalous" acceleration. So I don't come across as just…
dismissive... heres Loeb's claim (the original paper https://arxiv.org/abs/1810.11490) the key part being > From a theoretical point of view, Rafikov (2018) has shown that if outgassing was responsible for the acceleration (as originally proposed by Micheli et al. 2018), then the associated outgassing torques would have driven a rapid evolution in ‘Oumuamua’s spin, incompatible with observations. > If not cometary activity, what can drive the nongravitational acceleration observed? In this Letter we explore the possibility of ‘Oumuamua being a thin object accelerated by Solar radiation pressure, which would naturally result in an excess acceleration ∆a ∝ r^−2. The only evidence is basically one paper. Rafikov's https://arxiv.org/abs/1809.06389 and its not used for much beyond saying "it cant be outgassing" which is a bad interpretation since at the end of that paper Rafikov says. > Based on these arguments, as well as the lack of direct indicators of outgassing, we conclude that the classification of ’Oumuamua as a volatile-rich comet is dubious and raises more questions than it provides explanations. > We encourage further analyses of the astrometric data to better characterize its anomalous acceleration (Micheli et al. 2018). Settling the issue of whether this unique object has asteroidal or cometary composition is crucial for understanding its origin (Rafikov 2018a). So as a moderately science literate person on the outside, it just feels like initial paper was idle conjecture not serious science, and now he's so deep in the hole even Lassie cant save him now... So he wrote a book to make money instead.
Here's the paper Loeb co-authored ... Could Solar Radiation Pressure Explain 'Oumuamua's Peculiar Acceleration? https://arxiv.org/abs/1810.11490v4
The following October, Avi Loeb, the chair of Harvard’s astronomy department, co-wrote a paper (with a Harvard postdoctoral fellow, Shmuel Bialy) that examined ‘Oumuamua’s “peculiar acceleration” and suggested that the object “may be a fully operational probe sent intentionally to Earth’s vicinity by an alien civilization.” The referenced paper is here: Could Solar Radiation Pressure Explain 'Oumuamua's Peculiar Acceleration? https://arxiv.org/abs/1810.11490
Well, the paper[0] spends ~98% of the time not claiming that. I think I thought those pictures of it were what it looked like! but "The large variations on the light curves indicate that ʻOumuamua is a highly elongated object... However, the size and shape have not been directly observed as ʻOumuamua appears as nothing more than a point source of light even in the most powerful telescopes. Neither the albedo or triaxial ellipsoid shape are precisely known."[1] [0] https://arxiv.org/pdf/1810.11490.pdf [1] https://en.wikipedia.org/wiki/%CA%BBOumuamua
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