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How common is H2 forming under a shell of normal ice, among comets?

The context is the Oumuamua discussion, and its latest tentative solution. "Acceleration of 1I/‘Oumuamua from radiolytically produced H2 in H2O ice" https://www.nature.com/articles/s41586-022-05687-w

Is formation of H2 in comets has discussed for long "The possible formation of a hydrogen coma around comets at large heliocentric distances" https://ui.adsabs.harvard.edu/abs/1988ApJ...324L..31B/abstract

...but has it been observed before? Or is Oumuamua perhaps its first observation?

Mark Besser
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    It's never been observed, that's the problem. Hydrogen is invisible at temperature below several thousand K. – AtmosphericPrisonEscape Mar 23 '23 at 11:33
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    Do you have access to the text of the nature article? Their first three paragraphs outline how a) H2 is non-detectable in the wavelengths that were observed and b) gives a list of laboratory experiments that show H2 production in porous H2O ices in lab settings. – AtmosphericPrisonEscape Mar 23 '23 at 17:34
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    @AtmosphericPrisonEscape "Hydrogen is invisible at temperature below several thousand K." Maybe in visible, but what about far infrared and radio? – uhoh Mar 24 '23 at 12:42
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    @AtmosphericPrisonEscape Unfortunately not, but their datasets are open "The datasets generated and analysed during the current study are available on GitHub at https://github.com/bergnerjb/Oumuamua_H2." – Mark Besser Mar 24 '23 at 13:10
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    @MarkBesser The data they are analysing there, are the trajectories of the object under the presumed hydrogen outgassing, which they model using the code Mercury. The data generated and available is that simulation data. So those are not experimental datasets. You could try "other sources" on the internet cough to get your hands on this article... – AtmosphericPrisonEscape Mar 24 '23 at 14:40
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    @uhoh Quadrupole and spin-transitions are way too faint to measure $H_2$ outgassing from comets, they are even too faint to measure protoplanetary disc masses. – AtmosphericPrisonEscape Mar 24 '23 at 14:50
  • @AtmosphericPrisonEscape okay got it, thanks! – uhoh Mar 24 '23 at 21:23

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