Themisto is the ninth moon of Jupiter; a small, irregular moon that orbits inside, and does not belong to, the two main dynamical clusters of jovian irregular moons. Its discovery was announced in 2000 by Scott Sheppard, David Jewitt, Yan Fernandez, and Eugene Magnier. Themisto has a prograde (direct) orbit with an orbital radius of approximately 100 Jupiter radii. It is also known as Jupiter XVIII and was formerly known as S/2000 J1.