In his later career, Herschel discovered two moons of Saturn, Mimas and Enceladus; as well as two moons of Uranus, Titania and Oberon. He did not give these moons their names; they were named by his son John in 1847 and 1852, respectively, after his death. Herschel measured the axial tilt of Mars and discovered that the Martian ice caps, first observed by Giovanni Domenico Cassini (1666) and Christiaan Huygens (1672), changed size with that planet's seasons. It has been suggested that Herschel discovered rings around Uranus.