Researchers at NASA’s Jet Propulsion Laboratory (JPL) have discovered two small moons around Neptune perform a “dance of avoidance” as they orbit the planet.
Naiad and Thalassa were discovered by NASA’s Voyager 2 spacecraft as it passed by the ice giant Neptune in 1989. In a paper published on November 13, researchers at JPL revealed that the two moons follow a strange orbital pattern unlike any observed before.
“We refer to this repeating pattern as a resonance,” said Marina Brozović, an expert in solar system dynamics at JPL and the lead author of the new paper, which was published in the scientific journal Icarus. “There are many different types of ‘dances’ that planets, moons and asteroids can follow, but this one has never been seen before.”
In this perpetual orbital ballet, Thalassa is the strong backbone and is in a stable seven-hour orbit around the ice giant. Naiad, on the other hand, brings flair to the duo. The moon orbits the planet every seven and a half hours in a wild zigzag pattern. As it catches Thalassa every four orbits, it bucks up and down around its orbital partner passing as close as 1,850 kilometers.
If you were on the surface as Naiad caught up to Thalassa, you would likely see it pass twice from above and twice from below. Approximately 21 hours later, it would be back again sailing up and down in an endless cosmic ballet.
Researchers at JPL believe that Naiad’s tilted orbit is a result of an interaction with one of the ice giant’s other inner moons.
“We suspect that Naiad was kicked into its tilted orbit by an earlier interaction with one of Neptune’s other inner moons,” said Brozović. “Only later, after its orbital tilt was established, could Naiad settle into this unusual resonance with Thalassa.”
