Astrophysics is not always easy for astrophysicists: just when they realize another aspect of the motion patterns in our Solar System, come two of Neptune's moons to beautify everything.
The two moons concerned are Najad and Talasa, both about 100 kilometers or 62 miles wide, orbiting their planet in what NASA researchers call a "dance of evasion."
Compared to the Talas, Najad's orbit is about five degrees – she spends half her time over the Talas and half of it below, in a related orbit unlike anything else.
"We refer to this repetitive pattern as a resonance," says physicist Marina Brozovic, of NASA's Aircraft Laboratory. "There are many different types of dances that can follow planets, moons and asteroids, but this has never been seen."
The orbits of the two small moons are only 1,850 kilometers away, but they are perfectly timed and choreographed to avoid each other. Najad takes seven hours to round Neptune, while Talasa takes seven and a half on the outer path.
If you were stationed at Talassa, you would see Niyad going up and down in a pattern that would be repeated every four loops, because Niyad constantly laments his neighbor. Researchers say these maneuvers keep the orbits stable.
The team used data collected between 1981 and 2016 from Earth telescopes, Voyager 2 and the Hubble Space Telescope to determine how Najad and Talasa gather around the next giant they call home.
These moons are two of the 14 satellites confirmed for Neptune, and two of the seven so-called inner moons, a very tightly packed system intertwined with weak rings.
According to researchers, capturing the large moon Neptune Triton could explain where Nayad and Talasa came from and how they orbit their planet in such an unusual way.
The inner moons may represent debris from Triton, the team suggests, with Nayad eventually launching into its tilted orbit by interacting with another of these close neighbors.
In addition to drawing the orbits of Najad and Talasa, the new study has also taken the first steps toward determining the composition of Neptune's inner moons, which appear to be made up of something like ice water.
"We're always excited to find these interdependencies between moons," says planetary astronomer Mark Fowlter of the SETI Institute.
"Nayad and Talasa are probably locked into this configuration for a very long time because it makes their orbits more stable. They keep the peace by never coming close. "
The research is published in Icarus.