Neso/ˈniːsoʊ/, also known as Neptune XIII, is the second-outermost known natural satellite of Neptune, after S/2021 N 1. It is a retrogradeirregular moon discovered by Matthew J. Holman, Brett J. Gladman, et al. on 14 August 2002, though it went unnoticed until 2003.[2][8] Neso is the second-most distant moon of Neptune, with an average orbital distance of nearly 49.6 million km. At its farthest point of its orbit, the satellite is more than 72 million km from Neptune. This distance exceeds Mercury's aphelion, which is approximately 70 million km from the Sun.
Irregular satellites of Neptune
Neso is also the moon with the second-longest orbital period, 26.67 years. It follows a retrograde, highly inclined, and highly eccentric orbit illustrated on the diagram in relation to other irregular satellites of Neptune. The satellites above the horizontal axis are prograde, the satellites beneath it are retrograde. The yellow segments extend from the pericentre to the apocentre, showing the eccentricity.
Neso is about 60 km (37 mi) in diameter based on an assumed albedo of 0.04.
Given the similarity of the orbit's parameters with Psamathe (S/2003 N 1), it was suggested that both irregular satellites could have a common origin in the break-up of a larger moon.[5]
Neso is named after one of the Nereids. Before it was officially named on 3 February 2007 (IAUC 8802), Neso was known by its provisional designation, S/2002 N 4.
^ ab
Green, Daniel W. E. (1 October 2003). "S/2001 U 2 and S/2002 N 4". IAU Circular. 8213. Retrieved 24 October 2011.
^ ab"Natural Satellites Ephemeris Service". Minor Planet Center. Retrieved 14 June 2023. Selection of Objects → "All Neptunian outer irregular satellites" → Check "I require Orbital Elements" → Get Information
