Curator Ali Boyle and Press Officer Will Stanley reflect on our most distant (dwarf) planet, Pluto.
The successful flyby of Pluto on 14 July 2015 by NASA’s New Horizons spacecraft means that humans have now explored (with robotic assistance) every planet in our solar system. New Horizons flew within 7,750m of Pluto, travelling at 31,000mph as it sped past the (dwarf) planet that lies 3 billion miles from our home.
This historic flyby completes a quest that began in the 1960s with NASA’s Mariner and the Soviet Venera missions to Venus. You can see an engineering test model of Venera 7 in our Cosmonauts exhibition from September 2015.
New Horizons is capturing high resolution images and scientific data, but can only send images back to Earth at 1 kilobit per second, fifty times slower than a 56k modem from the 1990s. Even travelling at the speed of light, it takes almost four and a half hours for the data to reach Earth.
A device similar to this CCD (Charge Coupled Device), on display in our Exploring Space gallery, will capture the first close up images of Pluto ever taken. Made by British company e2v, the CCD will be used in the PERSI (Pluto Exploration Remote Sensing Investigation) Ralph telescope, with a similar device in the spacecraft’s LORRI (Long Range Reconnaissance Imager) instrument.
The first discovery photographs of Pluto where taken in February 1930, by a young American astronomer. At the time Clyde Tombaugh was searching for a predicted ‘Planet X’ that might explain oddities in the orbits of Neptune and Uranus.
Tombaugh spent months painstakingly photographing the same sections of sky and studying the images with a blink comparator. On 18 February 1930, he noticed that on photographs taken a few nights apart that January, one ‘star’ had moved, indicating that it was actually a nearby object moving against the fixed background of distant stars. You can see a glass positive of the photograph in our Cosmos and Culture exhibition.
Further observations confirmed the discovery, which was announced to the world in March 1930. Despite the fanfare, Pluto turned out not to be Planet X – Tombaugh had just been looking in the right place at the right time. Subsequent observations revealed that Pluto was too small to match the predictions. Eventually, revised calculations of Neptune and Uranus’s orbits removed the need for Planet X altogether.
Thanks to New Horizons, Tombaugh has come closer to Pluto than anyone else as some of his ashes are on board the spacecraft.
By the 2000s, astronomers had discovered a slew of similarly-sized bodies beyond Neptune. Either our Solar System had a lot more planets than anyone had realised, or it was time to rethink what counts as a planet.
On 24 August 2006 the International Astronomical Union voted on a new definition, demoting Pluto to ‘dwarf planet’. ‘Save Pluto’ campaigns were quick to follow, and these bumper stickers (also on display in the Cosmos and Culture exhibition) were some of the first products to go on sale.
The IAU’s definition of ‘planet’ remains controversial, so there may be hope for Pluto yet. Until July 2015 we knew very little about Pluto as it was so faint and far away, but with new images and scientific data we can finally discover the secrets of this (dwarf) planet, three billion miles away.