The planet farthest from the Sun has a rather strange collection of moons in its orbit. This may be because Neptune’s largest moon, Triton, caused a disaster when it entered the planet’s orbit billions of years ago. Now, scientists suggest that Neptune’s original set of moons was violently destroyed by Triton’s violent entry, except for one.
Using data from the Webb Space Telescope, a team of researchers suggests that Neptune’s moon Nereid is the only 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 information about the chaotic history of the solar system and how it changed over billions of years.
making an entry
Neptune’s moon Triton was discovered just 17 days after the planet itself. It is almost the size of Earth’s Moon, much larger than any of Neptune’s other moons. Triton orbits in the opposite direction of its planet’s rotation, the only large moon in the solar system to display such strange behavior.
Because of its strange qualities, scientists believe that Triton did not form from the remains of Neptune’s formation. Instead, it may be a Kuiper Belt object that was attracted and captured by Neptune’s gravity almost 4 billion years ago. When it entered orbit around Neptune, Triton may have caused great chaos, disrupting the planet’s satellite system.
Another strange moon orbiting Neptune is Nereid. It is the third largest moon of Neptune and has the most eccentric orbit of all the moons 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 Nereid may also have been captured by Neptune’s gravity.
The new study, however, suggests that, rather than sharing a common origin story, Triton and Nereid may be long-time enemies.
Surviving Triton
The researchers behind the study, led by first author Matthew Belyakov of the California Institute of Technology, observed Nereid for a total of 10 minutes and 40 seconds using Webb’s infrared capabilities. They found that the moon was rich in water on the surface and brighter than many Kuiper Belt objects. Instead, Nereid’s overall signature was more similar to that of the moons around Uranus.
The researchers then ran computer simulations to test whether Nereid could have been part of Neptune’s original moon crew. In simulations in which Triton crashed into the Neptune satellite system, one or more moons survived in irregular orbits about 20% of the time.
The study suggests that within the solar system’s first 200 million years, Triton’s forced entry into Neptune’s orbit would likely have destroyed the planet’s original set of moons. Nereid, on the other hand, may have been saved and launched into an eccentric orbit.
That leaves Nereid as the sole survivor of an ancient lunar collision that destroyed its fellow satellites and left it further from its host planet. It’s an incredible story, with young Neptune thrown into chaos by the arrival of Triton and Nereid emerging as the only surviving relic of the planet’s original family of moons.
