NASA's Hubble catches a pair of Neptune's moons in a truly bizarre 'dance of avoidance'

Naiad and Thalassa are two of Neptune's innermost moons that exist pretty close to each other.


The eighth planet in the solar system, Neptune, has 14 moons and they all rotate around the planet at their own pace. Recently, scientists at NASA’s Jet Propulsion Laboratory (JPL) discovered that two of the ice giant’s moons — Naiad and Thalassa — are locked in a 'dance of avoidance'.

These two Neptunian satellites are fairly close to one other — some 1,850 kilometres apart. When they pass each other, they are around 3,540 kilometres apart.

NASAs Hubble catches a pair of Neptunes moons in a truly bizarre dance of avoidance

Two of Neptune's moons are caught in an odd dance of avoidance. Image: NASA

Naiad moves a lot quicker than Thalassa and dances around the other moon in an effort to avoid a head-on collision. They do not collide into each other because Naiad’s orbit is tilted at about 5 degrees. Naiad takes seven hours to complete one rotation around Neptune while Thalassa completes it in seven and a half hours.

If you were to live on Thalassa, you would see Naiad go up and down in a zigzag pattern, passing by twice from above and then twice from below. While scientists do not know how the two moons came to perfect this routine, they do have a few working theories.

The first possibility is that an original satellite system was disrupted when Neptune captured its giant moon Triton, which led to the inner moons and rings forming from the leftover debris. [Neptunes has a total of six rings.]

Relative sizes of a few of Neptune’s moons, including Hippocamp. Image credit: Mark Showalter/SETI Institute

Relative sizes of a few of Neptune’s moons, including Hippocamp. Image credit: Mark Showalter/SETI Institute

"We suspect that Naiad was kicked into its tilted orbit by an earlier interaction with one of Neptune's other inner moons," said Marina Brozović, an expert in solar system dynamics at JPL in a press release. "Only later, after its orbital tilt was established, could Naiad settle into this unusual resonance with Thalassa."

"Naiad and Thalassa have probably been locked together in this configuration for a very long time, because it makes their orbits more stable. They maintain peace by never getting too close," Mark Showalter, a planetary astronomer at the SETI Institute and a co-author of the new paper said in a press release.

Data collected between 1981 and 2016 from NASA’s Hubble telescope and Voyager 2 (the only spacecraft to visit Neptune first hand on its way out of the solar system)and other space telescopes on Earth helped in the discovery of this unusual orbital pattern. The study also said that the moons are largely made up of water ice.

The study and its findings were published in the journal Icarus.

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