Neptune’s moon Nereid could be the sole survivor of an historic moonpocalypse.
A brand new examine means that the unusual satellite tv for pc was born in a gentle, round orbit round Neptune, then tossed into its present elongated orbit throughout a chaotic encounter with a Pluto-sized physique that ejected or pulverized all its sibling moons. This concept counters the belief that Nereid shaped within the Kuiper Belt, the chilly reservoir of area rocks within the outer photo voltaic system, and was pitched into its current orbit later, researchers argue Might 20 in Science Advances.
“Perhaps it obtained perturbed outward, reasonably than kicked inward,” says planetary scientist Matthew Belyakov of Caltech. “Nereid is that final remaining signature of the unique satellite tv for pc system.”
Neptune’s largest moon, Triton, orbits backward and makes up greater than 99 p.c of the mass of all of the planet’s moons mixed. Most of Neptune’s different moons orbit the planet from a shorter distance and are small and rubbly, suggesting they’ve been by a number of collisions. Planetary scientists assume Triton got here from the Kuiper Belt and wreaked havoc on the remainder of the moons when Neptune captured it billions of years in the past.
Nereid stands alone. It orbits in a large ellipse removed from Neptune. That places it in a household of moons from throughout the photo voltaic system referred to as irregular satellites, lots of that are additionally considered captured Kuiper Belt objects. However it’s brighter, bigger, extra eccentric and nearer to its host planet than different irregular satellites within the photo voltaic system. “Nereid at all times is an outlier,” Belyakov says. Perhaps its origin story was an outlier, too.
Belyakov and colleagues in contrast James Webb House Telescope observations of Nereid’s make-up with these of different Kuiper Belt objects. Nereid wasn’t an excellent match for any of them.
That left the likelihood that Nereid shaped domestically. Belyakov and colleagues ran pc simulations of Triton’s identified chaotic arrival at lots of of various lots and orbits for Neptune’s authentic moons, together with the destroyed ones.
None reproduced Nereid’s precise present-day orbit. And a few ended with Triton leaving the system or crashing into Neptune. However about 20 p.c produced a moon on a Nereid-like orbit, with out destroying Triton. That’s sufficient to make the story plausible, Belyakov says.
Nereid itself continues to be largely mysterious. The perfect image we now have of it’s about 5 pixels throughout, from the Voyager 2 mission in 1989. Belyakov is holding out for a spacecraft flyby sometime. “That’s the following frontier, missions to the ice giants,” he says.
