THE DISCOVERY

THE PLUTO DISCOVERY

The search for the elusive ninth planet had been ongoing for over three decades since the turn of the 20th century. Precise observations of the orbits of Uranus and Neptune had suggested another distant world lurking in the darkness beyond Neptune. However, locating such a faint object was like searching for a needle in the celestial haystack. Leading the hunt for Planet X during this time was Percival Lowell, founder of the Flagstaff Observatory. Starting in 1906, Lowell had embarked on an obsessive pursuit of the ninth planet. Despite years of work though, he would not live to see its discovery, nor know how close he had come to finding it himself. Unbeknownst to Lowell, images of Planet X had been captured in two photographs he took just a year before his death in 1916. However, the evidence was overlooked as the plates were filed away, and the search continued without him for another 15 years.

The logic behind using identical pairs of photographs taken nights apart was simple: by comparing the two images, they could differentiate between the fixed background stars and anything orbiting closer to Earth. Hundreds of image pairs were taken and analyzed at Lowell Observatory using a blink comparator, which helped reveal minute differences. It wasn't until the night of January 29, 1930 that Clyde Tombaugh would strike gold. Comparing two images taken a week apart, Tombaugh discovered what would finally be confirmed as Pluto.

The discovery of Pluto was a long process. In the early 1900s, astronomer Clyde Tombaugh compared photographic plates showing the same region of sky taken on different nights. Over several days, a faint spot had moved no more than an inch against the background stars. This tiny movement signified a profound discovery - an object much closer than the distant stars, shifting as the Earth's orbit changed perspective. Tombaugh had found "Planet X", later named Pluto after a suggestion by Venetia Burney, an 11-year-old English schoolgirl interested in mythology.

In January 2006, NASA launched the New Horizons probe to explore Pluto, nine years after Tombaugh's death. The piano-sized probe carried a tribute - 30 grams of his ashes. For mission leader Alan Stern, this fulfilled a promise made to Tombaugh before the mission began. When New Horizons launched on an Atlas V rocket, it started an epic journey across the solar system to explore Earth's last unvisited planet.

Travelling faster than any previous probe at over 16 km/s, New Horizons used a gravity assist from Jupiter to hurtle onwards. For most of the 8-year voyage, non-essential systems were shut down to conserve energy. While the probe slept, the New Horizons team could only wait and hope that their 20 years of planning would successfully deliver the probe to explore mysterious Pluto.

New Horizons was launched from Earth at a record-breaking speed, reaching Jupiter in just over a year for a gravity-assisted boost that propelled it across the solar system. After two decades of planning and eager anticipation, the New Horizons team could only wait and hope as the intrepid probe raced in hibernation towards mysterious Pluto, the last unexplored planet in our solar system. This historic mission forged an inspiring human connection between the New Horizons scientists and the long-ago astronomer who first detected Pluto, a bond between explorers across time. It was spotted 136199 Eris, a world almost the same size as Pluto itself, if not bigger. These discoveries and the hundreds we've made since, forced the International Astronomical Union (the ruling body on Earth for all things astronomical) to formally reconsider the definition of a planet in October 2006. They published a set of three criteria that any object in our solar system would have to fulfill if it wanted to stake a claim as a planet:

1) It has to orbit the sun.

2) It has to be massive enough to form a sphere under its own gravity.

3) It has to be massive enough to clear its own orbit of any other objects, dust or debris.