An icy world on the outskirts of our solar system, Pluto was discovered by Clyde Tombaugh in 1930. It has puzzled astronomers and planetary scientists ever since, who have argued over the decades about Pluto’s origin, size, mass, composition and classification. It’s beyond doubt that Pluto is a fascinating body, with new properties revealed each time we look at it more closely.
Pluto has a strange elliptical orbit and forms part of the Kuiper Belt of outer solar system objects. It receives so little sunlight that the surface temperature is a chilly 30-55 Kelvin - so cold that nitrogen is a solid. Nevertheless there is an active surface geology and a tenuous atmosphere. Its moon Charon, discovered in 1978, is almost as big as Pluto itself and so massive that the two bodies orbit around each other.
The twenty-first century has seen an explosion of interest in Pluto. Four new moons have been discovered: Styx, Nix, Kerberos and Hydra. NASA’s New Horizons spacecraft became the first to visit Pluto in July 2015, flying through the system at high speed before sending back a wealth of new data on the system. One thing is certain: Pluto will continue to surprise us for years to come.