Using data from the Webb Space Telescope, a team of researchers is suggesting that Neptune’s moon Nereid is the sole survivor of the ancient lunar collision that rewrote the history of the planet’s orbital satellites. In a recent study published in Science Advances, researchers provide new insights into the chaotic history of the Solar System and how it changed over billions of years.
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Neptune’s moon Triton was discovered just 17 days after the planet. It is approximately the size of Earth’s moon, much larger than Neptune’s other moons. Triton orbits in the opposite direction to its planet’s rotation, making it the only large moon in the Solar System to exhibit such strange behavior.
Because of its strange properties, scientists believe that Triton was not formed from the remains of Neptune’s formation. Instead, it may be a Kuiper Belt object that was pulled in and captured by Neptune’s gravity about 4 billion years ago. As it entered Neptune’s orbit, Triton would have caused considerable chaos, disrupting the planet’s satellite system.
Another strange moon orbiting Neptune is Nereid. The third largest of Neptune’s moons, it has the most eccentric orbit of any moon in the Solar System. As one of the outermost moons around Neptune, it takes 360 Earth days to complete one orbit around its host planet. Its strange orbit suggests that the Nereid may also have been captured by Neptune’s gravity.
However, the new study suggests that rather than sharing a common origin story, Triton and the Nereid may have been longtime enemies.
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The researchers behind the study, led by first author Matthew Belyakov of the California Institute of Technology, observed the Nereid for a total of 10 minutes and 40 seconds using Webb’s infrared capabilities. They found that water is abundant on the moon’s surface and is brighter than many Kuiper Belt objects. Instead, the overall signature of the Nereid was similar to that of moons found around Uranus.
The researchers then ran computer simulations to test whether the Nereid might have been part of the original constellation of Neptune’s moons. In simulations where Triton crashed through Neptune’s satellite system, one or more moons survived in irregular orbits about 20% of the time.
The study suggests that within the first 200 million years of the Solar System, Triton’s forced entry into Neptune’s orbit may have destroyed the planet’s original set of moons. The Nereid, on the other hand, may have been rescued and sent outward into an eccentric orbit.
This makes Nereid the sole survivor of the ancient lunar collision that destroyed its satellite companions and left it far from its host planet. It’s a tale of hell, with young Neptune thrown into chaos by the arrival of Triton and the Nereid emerging as the only surviving remnant of the planet’s original family of moons.
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