There is yet another difficulty with the outgassing-comet hypothesis, regardless of whether ‘Oumuamua outgassed pure hydrogen or not. Its acceleration during deviation was smooth and steady. Comets are ungainly rocks; their rough and irregular surfaces retain unevenly distributed ice. As the Sun melts the ice and the outgassing produces propulsion, it does so across that rough and pitted surface. The result is what you would expect—a herky-jerky acceleration. But that is not what we saw ‘Oumuamua do. In fact, it did the very opposite of that. The odds of a naturally occurring comet composed of
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