Neso, also known as Neptune XIII, is the outermost natural satellite of Neptune. It is an Irregular moon discovered by Matthew J. Holman, Brett J. Gladman, et al. on August 14, 2002, though it went unnoticed until 2003. Neso orbits Neptune at a distance of more than 48 Gm (million km), making it (as of 2015) the most distant known moon of any planet. At apocenter, the satellite is more than 72 Gm from Neptune. This distance is great enough to exceed Mercury's aphelion, which is approximately 70 Gm from the Sun.