Surprisingly simple explanation for alien comet ’Oumuamua’s weird orbit

An artist's depiction of the interstellar comet 'Oumuamua, as it warmed up in its approach to the sun and outgassed hydrogen (white mist), which slightly altered its orbit. The comet, which is most likely pancake-shaped, is the first known object other than dust grains to visit our solar system from another star. In 2017, a mysterious comet dubbed 'Oumuamua fired the imaginations of scientists and the public alike. It was the first known visitor from outside our solar system, it had no bright coma or dust tail, like most comets, and a peculiar shape - something between a cigar and a pancake - and its small size more befitted an asteroid than a comet. But the fact that it was accelerating away from the sun in a way that astronomers could not explain perplexed scientists, leading some to suggest that it was an alien spaceship. Now, a University of California, Berkeley, astrochemist and a Cornell University astronomer argue that the comet's mysterious deviations from a hyperbolic path around the sun can be explained by a simple physical mechanism likely common among many icy comets: outgassing of hydrogen as the comet warmed up in the sunlight. What made 'Oumuamua different from every other well-studied comet in our solar system was its size: It was so small that its gravitational deflection around the sun was slightly altered by the tiny push created when hydrogen gas spurted out of the ice.