CircleCare 13th March 1930 – The discovery of Pluto was announced CircleCare The discovery of a ninth planet (Pluto) was announced by Clyde W. Tombaugh. Pluto is a dwarf planet in the Kuiper belt with a radius of 1,188 km and an orbital period of 248 years. On This Day CircleCare 9th, Circle Care, circlecare, Dwarf Planet, Planet