The orbits of Neptune’s two innermost moons are very odd, according to new research released by NASA. This planet boasts at least 14 moons. Neso, the farthest-flung of them, orbits in an extremely elliptical loop carrying it almost 46 million miles (74 million km) away from the planet, taking 27 years to complete. Naiad and Thalassa are small and shaped like Tic Tacs, spanning only about 60 miles (100 km) in length. Orbital dynamics experts have dubbed the cosmic choreography of these tiny moons as a “dance of avoidance”. The pair orbit Neptune only 1,150 miles (1,850km) apart, yet they miraculously always manage to miss each other as Naiad’s orbit is tilted and perfectly timed.
Every time the moon passes the slower-moving Thalassa, the couple move 2,200 miles (3,540km) apart. These trajectories sees Naiad hurtle around the frozen planet every seven hours, while the closer Thalassa takes half an hour more. An astronaut sitting on Thalassa would see Naiad in an apparently wild zigzagging orbit, passing by twice from above and then twice from below.
This pattern repeats every time Naiad gains four laps on Thalassa. And NASA has revealed how although the dance may appear odd, it keeps the orbits stable. Marina Brozović, an expert in solar system dynamics at NASA, said: “We refer to this repeating pattern as a resonance. “There are many different types of ‘dances’ that planets, moons and asteroids can follow, but this one has never been seen before.”
Source (NASA news: Space agency announces Neptune moons ‘dance’ to avoid cosmic collision, Express, 17.11.2019)