I feel sorry for Pluto. When I was younger it was the ninth biggest planet in the solar system, but unfortunately is now (probably) only the second biggest “dwarf planet” following the discovery of minor-planet 136199 Eris by the Palomar Observatory on January 5th 2005. This discovery encouraged an acceleration of the debate over whether or not Pluto should ever have been called a planet, the result being that the IAU published their Definition of a Planet in the Solar System on August 24th 2006. So I suppose that’s the day on which Pluto stopped being a planet, and became a Kuiper Belt Object. And as if that weren’t damage enough for Pluto’s image, there is still a debate going on as to whether Pluto and Charon should be re-classified as a binary system. At the moment Charon is a moon of Pluto; but the centre of their combined mass doesn’t lie within either body, so strictly speaking it should get higher billing.
On the upside, Pluto does get its own Disney character, and lends its name to both plutoids (anything beyond the orbit of Neptune that has managed to attain a roughly spherical shape) and plutinos (anything in the above group that orbits the Sun twice in the same time it takes Neptune to make it round three times).
Pluto was discovered on February 18th 1930 by Clyde Tombaugh from Illinois. Tombaugh was a prolific discoverer of variable stars, and also of asteroids, many of which he found while searching for Pluto. But Pluto will always be his claim to fame, and following his death in 1997 a small quantity of his ashes were sent on their way out there aboard the New Horizons probe, which arrived at the ex-planet on July 14th 2015 to a blaze of publicity, and began sending back fabulous snapshots.
And not before time, as you can see from the second photograph (below); because close-ups of Pluto from the enormous distance of the Earth don’t reveal a great deal of detail.
As well as the aforementioned Charon, Pluto has four other moons: Nix, Hydra, Kerberos and Styx. All moons of Pluto are named in accordance with the convention that they are mythological, and have some association with their parent (Hydra, for example, was the nine-headed guardian of an entrance to the underworld).
As I just mentioned, Pluto is a Kuiper Belt object (KBO). The Kuiper belt, (rhymes with sniper, not kipper, although I have to admit that I do find the concept of a kipper belt rather appealing) or, to give it its full name the Edgeworth-Kuiper Belt, stretches from about 30 to 50 AU from the Sun, and contains an enormous number of mostly smallish bodies (trans-Neptunian Objects, or TNOs) left over from the formation of the Solar System.
Why Edgeworth gets edged out in popular literature while Kuiper gets the kudos is something I might know more about by the time his birthday comes around (Feb 26th, 1880). Neither of them correctly predicted what the belt was like anyway, so it’s anybody’s guess.
Anyhoo, there are thought to be as many as 100,000 TNOs within the belt with a diameter of over 100km (which is why I say “smallish” not “small”) and, because Pluto is now a member, everybody knows the name of at least one.
Results from New Horizons are changing our view of Pluto for ever. It now see that a crust of water ice might be acting in place of a bedrock, supporting mountains made of frozen nitrogen and methane. It also seems that Pluto might, somehow, be still geologically active. We need to visit again!
February 18th, 1977 was the day on which the space shuttle Enterprise made her first “attached” flight. Strictly speaking, I suppose, this wasn’t the maiden flight of a shuttle, as Enterprise was securely strapped to the back of a specially adapted Boeing 747 for the duration. I now know that she didn’t have any engines or a heat shield, and was therefore incapable of actually flying in space, but at the time I was young(er), and mightily impressed (and it was the first time a shuttle’s wheels had been higher than the hangar roof, so it counts). I was even more impressed when Enterprise was flown, again attached to the 747, over the family home at Brown Edge, Staffordshire, six years later as part of a promotional tour of Europe, drumming up satellite launching business for NASA.