Astronomy: Explaining the acceleration of the interstellar object ‘Oumuamua

The previously unreconciled acceleration of the interstellar object ‘Oumuamua is due to the production of hydrogen gas from ice reserves, suggests a study published in Nature this week.

‘Oumuamua is the first known interstellar object to be monitored travelling through our Solar System, having originated outside the Solar System. It displays a small non-gravitational acceleration typically associated with the release of trapped gas from a material, as seen in comets. However, it displays no further typical tracers of cometary activity such as a ‘tail’ of dust or gas. These seemingly contradictory observations have made it difficult for researchers to precisely define the nature of ‘Oumuamua.

In a model developed by Jennifer Bergner and Darryl Seligman, the acceleration of ‘Oumuamua is attributed to the release of trapped molecular hydrogen from within the object. This hydrogen has been formed through energetic processing of water-rich ice as the body passed close to the Sun, and is subsequently released from the object, slightly bending its path through our Solar System. Such reactions have been demonstrated in existing experimental work, showing that molecular hydrogen is known to be produced and subsequently expelled under such conditions.

Importantly, this model helps us understand ‘Oumuamua’s unusual properties without requiring further fine-tuning. The findings support previous theories that ‘Oumuamua may have originated as an icy planetesimal — a small object formed during the early stages of planet formation — similar to Solar System comets.