Pluto, our favourite former planet, was discovered exactly 86 years ago today, when astronomer Clyde Tombaugh, peering into the skies from the Lowell Observatory in Arizona, caught a glimpse of it for the first time.
Tombaugh’s search was not a pioneering, go-it-alone project, though, with the American following in the footsteps of Percival Lowell, who died in 1916 and had spent years searching for ‘the ninth planet’.
Lowell had noticed a “wobble” in the orbits of both Uranus and Neptune and felt a ninth planet, not far beyond, was causing this with its gravitational pull.
1930: A discovery
In 1930, more than a decade after Lowell’s death, Tombaugh’s discovery added the crucial ninth character to our now defunct planetary mnemonic.
But who named the planet Pluto? A young girl in England called Venetia Phair, who heard of the discovery from her grandfather over breakfast that March, takes the credit.
“And for some reason I, after a short pause, said, ‘Why not call it Pluto?’” she recalled a week before the New Horizons mission took off. Phair’s grandfather was well connected with astronomers in London and got in touch, with nobody else having thought of what Phair felt was a “fairly obvious” choice of name.
Word soon travelled, over cable, to the US and, between the jigs and the reels, Phair’s knowledge that planets were named after mythological legends paid off.
1978-2006: A moon and a downgrade
In 1978, Charon, its moon, was discovered, but the size of the duo, combined, was never enough to cause neighbouring planets to wobble.
So, in 2006, the International Astronomical Union stripped Pluto of its planet tag, due to new rules that said planets must “clear the neighbourhood around its orbit.”
Since Pluto’s oblong orbit overlaps that of Neptune, it was disqualified, and called a dwarf planet instead.
2006-2016: A treasure trove of science
But by then NASA had committed to finding out more, having sent New Horizons into space to capture some images only a few months earlier.
A long wait ensued, as the 3bn km mission got underway and, largely speaking, stayed clear from view for many years. Then last summer things started kicking off. New Horizons was getting closer, capturing images from afar and homing in on its target.
Its closest point was 12,500km from Pluto’s surface, capturing amazingly clear images and resulting in scientific papers of such detail that we know its make-up, its structures, and even its icy volcanoes.
New Horizons didn’t hang around for long, though, taking shots of Pluto’s heart-shaped topography and whizzing on towards the Kuiper belt.
It left behind mounds of science, which we’re still digesting more than six months later, a broken-hearted lonely planet and hopes of even more discoveries beyond.
But all this wouldn’t be possible without Lowell’s leg work, Tombaugh’s discovery and Phair’s early-morning suggestion.