Even by the wild standards of the outer solar system, the strange orbits bearing the two innermost Neptune moons are unprecedented, according to studies just published.
Experts in orbital dynamics call it the "dance of escape" performed by the small moons of Naiad and Thalassa. The two are true partners, traveling only about 1
In this enduring choreography, Naiad revolves around the ice giant every seven hours, while Talasa, on the outer runway, takes seven and a half hours. An observer sitting on Thalassa will see Nayad in orbit, which differs wildly in a zigzag pattern, passing twice from above and then twice from below. This pattern up, up, down, down is repeated every time Naiad wins four Thalassa laps.
Although the dance may seem strange, it keeps the orbits stable, the researchers say.
"We refer to this recurring model as resonance," said Marina Brozovic, a solar system dynamics expert at NASA's Jet Propulsion Laboratory in Pasadena, California and lead author of the new book, which was published November 13 in Icarus . "There are many different types of 'dance' that planets, moons and asteroids can follow, but this one has never been seen before.
Far from pulling the Sun, the giant planets of the outer solar system are the dominant sources of gravity and together they boast dozens and dozens of moons. Some of these moons formed with their planets and never went anywhere; others were captured later, then locked into orbits dictated by their planets. Some orbit in the opposite direction, their planets rotate; others alternate orbits with each other, as if to avoid a collision.
Neptune has 14 confirmed moons. Nesso, the farthest of them, orbits in a wildly elliptical contour that carries it nearly 46 miles (74 million kilometers) from the planet and takes 27 years to complete.
Nayad and Thalassa are small and shaped like Teak Tacs, covering only about 60 miles (100 kilometers) in length. They are two of the seven inner moons of Neptune, part of a tightly packed system intertwined with weak rings.
So how did they get together – but separately? The original satellite system is believed to have been disrupted when Neptune captured its giant moon, Triton, and that these inner moons and rings were formed by debris from the debris.
"We suspect that Nayad was struck in his tilted orbit by an earlier interaction with one of the other inner moons of Neptune," said Brozovic. "Only later, after establishing its orbital inclination, can Nayad
Brozovich and her colleagues discovered the unusual orbital model using NASA's Hubble Space Telescope Observation. observations for to calculate their mass and therefore their density – which is close to that of water ice. "
" We are always excited to find these interdependencies between moons, "says Mark Scholter, a planetary astronomer at SETI Institute in Mountain View, California. , and co-author of the new book. "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 newest, most tiny moon of Neptune, probably a piece of the larger
Marina Brozovic et al. Orbits and resonances of the regular Neptune moons, Icarus (2019). Doi: 10.1016 / j.icarus.2019.113462, https://arxiv.org/abs/1910.13612
NASA Detects Neptune Moons Locked in Avoidance Dance (2019, November 15)
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