Recently, Bergner and Seligman explained the behavior of the first interstellar object, ‘Oumuamua, as a rare form of a quite common object, a comet. They claim it “began as an icy planetesimal that was irradiated at low temperatures by cosmic rays during its interstellar journey, and experienced warming during its passage through the Solar System. This explanation is supported by a large body of experimental work.”
But Avi Loeb disagrees: “In a new paper published recently in Nature — https://www.nature.com/articles/s41586-022-05687-w Acceleration of 1I/‘Oumuamua from radiolytically produced H2 in H2O ice — Jennifer Bergner and Darryl Seligman suggest that the peculiar acceleration observed by the first known interstellar object `Oumuamua, can be explained if `Oumuamua was made of water ice which was partly dissociated into hydrogen by cosmic-rays along its interstellar journey. In the abstract of the paper, the authors admit that past models involving a pure hydrogen iceberg or a pure nitrogen iceberg do not work due to theoretical or observational inconsistencies. In fact, the hydrogen iceberg model was proposed in a previous 2020 paper by Darryl Seligman himself. A few months later, I wrote a paper with Thiem Hoang, showing that heating by interstellar starlight would destroy hydrogen icebergs too quickly and not allow them to reach the solar system from their likely formation sites of giant molecular clouds.
https://www.nature.com/articles/s41586-022-05687-w
Read Hoang and Loeb’s response paper:
https://lweb.cfa.harvard.edu/~loeb/Hoang_Loeb_23.pdf
Essay:
https://avi-loeb.medium.com/oumuamua-was-not-a-hydrogen-water-iceberg-1dd2f7a6107f
https://arxiv.org/pdf/2208.00092.pdf
https://www.theguardian.com/world/2023/mar/24/harvard-physicist-pacific-expedition-first-interstellar-meteor
Win a real meteorite if you have a .edu email address: briankeating.com/list
In the new paper, Bergner and Seligman also point out that sublimation of a pure water iceberg cannot provide the full acceleration of `Oumuamua, as reported by Marco Micheli and collaborators in a 2018 Nature paper. Since the observed acceleration declined smoothly in inverse proportion to distance squared from the Sun, I suggested a few months later in a paper with my former postdoc Shmuel Bialy that `Oumuamua was a thin membrane, pushed by sunlight. Since nature does not make light sails, I suggested in follow-up papers and my book Extraterrestrial that `Oumuamua was possibly produced by an extraterrestrial technological civilization. Most recently, I proposed in a newly published paper that this form of thin space trash could represent a piece from a broken Dyson sphere, which was damaged by asteroid impacts.
Since Bergner and Seligman admit that a pure water iceberg or a pure hydrogen iceberg are not viable models for `Oumuamua, it is unclear how mixing two failing models would make a successful solution. In particular, when hydrogen evaporates from a water iceberg, it would give less kick to the water than to a pure hydrogen iceberg because of the higher molecular weight of water. Moreover, if hydrogen evaporates easily from water ice, then it would not survive the journey, just as in the case of a pure hydrogen iceberg. These issues are not addressed in the new paper.
Another concern is that comets often show jitter from jets as a result of uneven sublimation of ice on their surface, as well as a substantial evolution in their spin period as they evaporate, whereas none of these was evident in the case of `Oumuamua. This point was highlighted in a 2018 paper by Roman Rafikov, shedding doubt on a cometary origin for `Oumuamua’s excess acceleration away from the Sun.”
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