Neptun's moons dance around each other to avoid a collision
Neptune has 14 moons, and Neso, one of the most distantly placed moons orbits in a wide elliptical loop.
Scientists have observed one of Neptune’s moons doing a 'dance of avoidance', which is the name they have given to its behaviour.
Why does the moon dance?
Scientists say that one of Neptune’s moons, Thalassa, which rotates close to Naiad, orbits in a zigzag pattern as it passes twice from above and below the other moon.
The pattern is repeated after every fourth lap of Naiad. Naiad takes seven hours to rotate around Neptune whereas Thalassa takes seven and a half hours to do the same. Thalassa has an outer orbit relative to Naiad.
Naiad passes twice from above and then twice from below over Thalassa’s orbit. According to scientists both these moons Naiad and Thalassa are shaped like TicTacs. These are among the seven moons of Neptune's inner moon that work closely with each other.
The dance might appear random but it helps in keeping the orbits stable.
Marina Brozović, a solar system expert and lead author of the paper says, "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." The research was published in Icarus.
Planets in the outer part of the solar system have more effective gravity on their moons as compared to the sun. The orbits formed by the moons of the planets are mostly governed by the planets themselves. There are moons that have unique orbits, like movements in the opposite directions as compared to the planet, and swapping orbits with each other to prevent a collision, but this zigzag movement is the first of its kind.
How did they come together?
Scientists suggest that the original satellite system was disrupted when Neptune captured its giant moon, Triton. The moons found in the inner orbit of the planet are formed from the leftover debris.
The lead author of the study says, "We suspect that Naiad was kicked into its tilted orbit by an earlier interaction with one of Neptune's other inner moons. Only later, after its orbital tilt was established, could Naiad settle into this unusual resonance with Thalassa."
This unique orbit of Neptune’s moon was observed by NASA's Hubble Space Telescope. It also provided new information about the composition of Neptune's inner moons. The mass and densities of these moons are close to that of water ice.
Mark Showalter, the co-author of the paper says, "We are always excited to find these co-dependencies between moons. 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."
Neptune has 14 moons, and Neso, one of the most distantly placed moons orbits in a wide elliptical loop. This unique orbit makes Neso travel a larger distance and it takes 27 years to complete one circle of the planet. While orbiting around it covers 46 million miles (74 million kilometres).