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> Loeb explains that the sun's gravitational force would cause a natural object to move faster as it approaches, and eventually push the object back, causing it

by creato 6y ago

> Loeb explains that the sun's gravitational force would cause a natural object to move faster as it approaches, and eventually push the object back, causing it to move slower as it moves away. Loeb points out that this didn't occur with Oumuamua, which accelerated "slightly, but to a highly statistically significant extent" as it moved further and further away. This seems like a straightforward falsifiable claim. So, why is there controversy? Is this correct or not?

techdragon 6y ago
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 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 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 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 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.

by creato 6y ago

techdragon 6y ago

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 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 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 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 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.