New Delhi: Neptune is known to host 16 natural satellites today. Prior to the close flyby by Voyager 2 in August 1989, only two moons were known to orbit
Neptune, the largest, Triton, and the smaller one, Nereid. Nereid was discovered by the Dutch astronomer Gerard Kuiper in 1949, and has presented an enduring mystery since its discovery. Nereid follows an eccentric orbit around Neptune, at a great distance from the planet, but is not nearly as distant as irregular satellites around other giant planets, that are stray objects captured from the Asteroid or Kuiper belts. Scientists have debated the origins of Nereid for over 70 years, and were not able to conclusively determined if the moon was formed in place or captured from space.
Jupiter, Saturn and Uranus all have typical moon systems, with several large moons that orbit along the equatorial plane as the host satellites. These are believed to have formed from the material leftover from the birth of the planet itself. There are also irregular satellites on inclined orbits, that seem to be captured objects. Neptune has one large moon, Triton. Triton is in a retrograde orbit, moving clockwise around Neptune that orbits the Sun in a counterclockwise direction. This means that Triton did not form in place, and is a captured Kuiper Belt Object, similar to Pluto.
Clues from Webb
The researchers used the James Webb Space Telescope to observe the Neptunian moon system, and discovered that the composition of Nereid was different from other Kuiper belt objects, and was more similar to the moons of Uranus. The researchers also developed simulations to explore the evolution of Neptunian moons. The simulations indicate that Triton was captured by Neptune, that would have kicked any other moons into eccentric orbits similar to that of Nereid. This research also indicates that Nereid formed around Neptune and was not captured. A paper describing the research has been published in Science Advances.
