Life is not always easy for astrophysicists: just when they came up with another aspect of motion patterns in our solar system, two of the Neptune moons come together to confuse everything.
The two moons in question are Nayad and Thalassa, about 100 kilometers wide or 62 miles wide, competing around their planet in what NASA researchers call "escape dance."
Compared to Thalassa, Naiyad's orbit is tilted by about five degrees – it spends half its time above Thalassa and half of it below a connected orbit, which is unlike anything else on record.
"We refer to this recurring model as resonance," says physicist Marina Brozovic, of NASA's Jet Propulsion Laboratory. "There are many different types of dance that planets, moons and asteroids can follow, but this one has never been seen before."
The two small moons of the moons are only about 1
If you were located at Thalassa, you would see Naiad passing above and below in a pattern that would be repeated every four cycles, as Naiad repeatedly traveled around with his neighbor. According to the researchers, these maneuvers keep the orbits stable.
The team uses data collected between 1981 and 2016 by Earth Telescopes, Voyager 2, and the Hubble Space Telescope to determine how Nayad and Thalassa go around the ice giant they call home.
These moons are two of 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 the researchers, capturing the great moon of Neptune Triton can explain where Naiad and Thalassa originated and how they rotate around their planet in such an unusual way.
The inner moons may represent the remains of Triton, the team suggests, with Naiad being eventually kicked into its sloping orbit by interacting with another of these close neighbors.
In addition to outlining the orbits of Naiad and Thalassa, the new study also succeeded in making the first steps to determine the composition of the inner moons of Neptune, which appear to be composed of something like water ice.
"We are always excited to find these interdependencies between the moons," says planetary astronomer Mark Schoulter of the SETI Institute.
"Nayad and Thalassa have probably been locked together in this configuration for a very long time because this makes their orbits more stable. They keep the peace, never getting too close. "
The study was published in Icarus .