Its trajectory had deviations that could not be explained by the gravitational influence of the Sun alone.
There were several proposed theories to explain its behavior, including the possibility that it was an alien spaceship with onboard propulsion.
A team of researchers proposed a simple physical explanation for 'Oumuamua's acceleration away from its trajectory.
The researchers suggested that cosmic radiation could trap hydrogen within icy bodies like comets.
As 'Oumuamua approached the Sun, the trapped hydrogen was outgassed, providing the push that astronomers had observed.
The outgassing hydrogen provided sufficient force to make 'Oumuamua accelerate away from the Sun.
Previous studies had indicated that high-energy cosmic rays can penetrate deep within icy bodies, converting the water to hydrogen gas.