In 2017, astronomers discovered an object they named Oumuamua, which zipped through our solar system and left them puzzled about its origin. Initially thought to be an asteroid due to its lack of typical comet characteristics, further analysis revealed that it was, in fact, a comet propelled by minuscule amounts of hydrogen gas spurting from an icy core. This simple explanation was proposed by Jennifer Bergner, an astrochemist at the University of California, Berkeley, and Darryl Z. Seligman of Cornell University, in a paper published in Nature.
The hydrogen gas was produced when high-energy particles struck the ice of the comet, leaving tiny bubbles of hydrogen gas trapped several meters deep in the ice. Since Oumuamua was small, the release of gas produced enough force to power the acceleration, without leaving any observable comas or tails.
While the explanation is fascinating, the controversy surrounding Oumuamua’s origin continues. Avi Loeb, an astronomer at Harvard who proposed the theory that it could have been an alien artifact, disputed the new paper. Nevertheless, Karen Meech, a comet expert at the University of Hawaii’s Institute for Astronomy, who has extensively studied Oumuamua, called the paper “a very interesting explanation.”
Dr. Bergner and Dr. Seligman began collaborating on a solution to the Oumuamua mystery while working as postdoctoral fellows at the University of Chicago. According to Dr. Seligman, the nongravitational acceleration was strange, as they had never seen a comet in the solar system that didn’t have a dust coma. Dr. Bergner, an expert on the chemistry of ice in outer space, discovered that water ice in its amorphous form has a fluffy structure containing pockets where other volatile molecules can be trapped. As the ice is warmed, it rearranges to a more stable and compact structure, leading to the collapse of these pockets and the formation of channels within the ice, through which trapped gas can escape.
While there is much to learn about the nature of small bodies in the solar system, this discovery provides further support that Oumuamua originated as a planetesimal relic broadly similar to solar system comets. In conclusion, Oumuamua was a comet propelled by hydrogen gas spurting from an icy core, and while the debate over its origin continues, this finding sheds light on the fascinating mysteries of our universe.