Neptune’s moons locked in ‘dance of avoidance’

Neptune Moon Dance: This animation illustrates how the odd orbits of Neptune’s inner moons Naiad and Thalassa enable them to avoid each other as they race around the planet. (courtesy: JPL)

Well, this is fun. Need we say more?

Even by the wild standards of the outer solar system, the strange orbits that carry Neptune’s two innermost moons are unprecedented, according to newly published research.

Orbital dynamics experts are calling it a “dance of avoidance” performed by the tiny moons Naiad and Thalassa, says Space Newsfeed.

The two are true partners, orbiting only about 1,150 miles (1,850 kilometers) apart.

But they never get that close to each other; Naiad’s orbit is tilted and perfectly timed. Every time it passes the slower-moving Thalassa, the two are about 2,200 miles (3,540 kilometers) apart.

In this perpetual choreography, Naiad swirls around the ice giant every seven hours, while Thalassa, on the outside track, takes seven and a half hours.

An observer sitting on Thalassa would see Naiad in an orbit that varies wildly in a zigzag pattern, passing by twice from above and then twice from below. This up, up, down, down pattern repeats every time Naiad gains four laps on Thalassa.

Although the dance may appear odd, it keeps the orbits stable, researchers said.

“We refer to this repeating pattern as a resonance,” said Marina Brozovi, an expert in solar system dynamics at NASA’s Jet Propulsion Laboratory in Pasadena, California, and the lead author of the new paper, which was published Nov. 13 in Icarus. “There are many different types of ‘dances’ that planets, moons and asteroids can follow, but this one has never been seen before.”

Full report here.