What do Jennifer Bergner and colleagues propose as the cause of 'Oumuamua's nongravitational acceleration?

• A. The solar wind stripping of surface ice.
• B. Magnetic interactions with the solar wind.
• C. Dark matter interactions.
• D. The gaseous expulsion of entrapped hydrogen from its water-rich icy body.

Answer: (D)

Nongravitational acceleration on a small body can come from jets of gas escaping its surface, which push the object in the opposite direction like a rocket. Jennifer Bergner and colleagues suggest that Oumuamua could be a water-rich icy body with pockets of hydrogen gas trapped inside. As it warmed near the Sun, this hydrogen would be released as gas, producing a jet that provides the thrust needed to alter its trajectory. Because hydrogen gas can escape without producing a noticeable dusty coma or tail, this mechanism could explain the observed acceleration without the bright cometary signals we would expect if it were mainly outgassing water vapor or dust. The idea fits the data by linking the path change to a plausible gas-jet source that leaves little visible signature. Other possibilities—such as solar wind interactions, magnetic effects, or exotic scenarios—don’t align as neatly with the combination of measurable acceleration and the lack of dramatic outgassing features, making the hydrogen-jet explanation the strongest fit.