Pluto: 2 for 1

Hello….what have we here? 

Yes, two for the price of one and you can see this in real life - only if you have a powerful telescope and know where to look in the constellation of Sagittarius the Archer. 

Do you remember swatting for science tests with the mnemonic: "My Very Educated Mother Just Sent Us Nine Pizzas" for the 9 planets - 4 terrestrial (Earth-like), 4 gaseous and mysterious Pluto? 
Well you can forget the pizzas because they're now telling us that Pluto is too much of a misfit to be called a planet. It's much neater to just have 8 ‘peas in the pod’: 4 terrestrials and 4 gaseous, and demote Pluto to a dwarf planet or ‘TNO’- Trans Neptunian Object.                

The problem is the other ‘terrestrials’ aren’t really Earth-like, and the 8 planets certainly aren’t ‘peas in a pod’ but all very UNIQUE. (how come?)  No two planets are alike - but Pluto is just too unique!

Percival Lowell (1855-1916) looked for a Planet X that mistakenly seemed to influence the orbit of Uranus and Neptune.  Lo and behold!... a 22 year old amateur, Clyde Tombaugh found ‘tiny’ Pluto on 18 February, 1930. 
(The PL in ‘Pluto’ acknowledges Percival Lowell.)

So what do we know about Pluto?  

·       Believed to comprise rock and frozen methane
·       A methane atmosphere
·       Still active volcanically!  (The ‘god of the dead’ is not so dead!)
·       A retro rotation about an axial tilt of 122.53 degrees from its orbital plane
·       The coldest ‘planet’ in our solar system, at minus 225 degrees C  (cold enough?)
·       A solar orbit inclined 17 degrees, so elliptical that it passes inside the orbit of Neptune for 20 out of 248 Earth years
·       3 minor satellites known as: Nix, Hydra and P4

…and how about this?...     
In 1978, astronomer James Christy found Pluto had a sibling – a moon half its size, Charon (‘ferryman of the dead’), which orbits Pluto every 6.4 days and they constantly face each other in a ‘tidal lock’-
just like two angry brothers, very much alive, facing off for a fight in the freezer room!                                                                                                                                       

(Pssst!……..whatever did Jim’s wife, Char, think of having a frigid moon named after her?)