Pair of Neptune moons locked in 'dance of avoidance'

Nov. 15 (UPI) -- Two of Neptune's 14 moons are engaged in an orbital tango that ensures the neighboring satellites don't crash into one another.

Researchers discovered the unusual zigzagging orbital pattern of Naiad and Thalassa after analyzing data captured by NASA's Hubble Space Telescope. Scientists dubbed the pattern the "dance of avoidance."

Naiad and Thalassa are tiny moons shaped like tic tacs, measuring less than 60 miles from end to end. Though their orbital paths are just 1,150 miles apart, they never pass within 2,200 miles of each other.

Both satellites are inner moons. Naiad circles Neptune every seven hours, while Thalassa takes 7.5 hours to complete an orbit. Naiad's zigzag path ensures that it swings away from its neighbor each time it passes the slower Thalassa. For every four passes that Naiad makes, the moon passes Thalassa twice above and twice below.

Researchers described the novel orbital pattern in a paper published this week in the journal Icarus.

"We refer to this repeating pattern as a resonance," lead study author Marina Brozović, an expert in solar system dynamics at NASA's Jet Propulsion Laboratory in California, said in a news release. "There are many different types of 'dances' that planets, moons and asteroids can follow, but this one has never been seen before."

The two moons haven't always been locked in a neatly choreographed dance. Scientists suspect the trajectories of Neptune's satellite community were heavily influenced by a series of lunar collisions that occurred when the icy planet captured its largest moon, Triton, millions of years ago.

"We suspect that Naiad was kicked into its tilted orbit by an earlier interaction with one of Neptune's other inner moons," Brozović said. "Only later, after its orbital tilt was established, could Naiad settle into this unusual resonance with Thalassa."