Irregular moon Irregular moon In astronomy, an irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit. They have been captured by their parent planet, unlike regular satellites, which formed in orbit around them. As of July 2018, 125 irregular moons are known, orbiting all four of the outer planets (Jupiter, Saturn, Uranus and Neptune). The largest of each planet are Himalia of Jupiter, Phoebe of Saturn, Sycorax of Uranus, and Triton of Neptune. It is currently thought that the irregular satellites were captured from heliocentric orbits near their current
Fictional planets of the Solar System fragments of a single planet was gradually abandoned over the course of the middle decades of the 20th century in favor of the conclusion that no planet had ever accreted in the region of the asteroid belt in the first place. In fiction, various other names were given to the same or similar concepts. Fictional planets in our Solar System beyond the orbit of Neptune have been employed many times as settings or references in science fiction. Following the general reception of Pluto as the ninth planet of the Solar System in 1930, a hypothetical additional planet was sometimes called