Pluto‘s biggest moon, Charon, was discovered on June 22nd, 1978 by American astronomer James W Christy at the United States Naval Observatory.
Until recently, Charon, like Pluto, was mostly a collection of blurry smudges on photographic plates, but thanks to the 2015 flyby of NASA’s New Horizons mission, they both suddenly got a lot closer.
At just over 1,000 km wide, Charon is quite small. But because Pluto is also rather diminutive, Charon has a much greater effect on its host than the average satellite, particularly regarding the location of their barycentre, or the point in space about which their two-body system orbits. Whereas the effect of our own Moon is only enough to move the barycentre slightly away from the centre of the Earth and produce a small “wobble” because the relative masses of the two bodies are so different, Charon is so big relative to Pluto that they orbit a point well outside the surface of Pluto. This has led some to argue that the Pluto-Charon system should be considered as a binary system, rather than a dwarf planet/moon arrangement.
Charon’s orbit of Pluto is almost completely circular, with an eccentricity of 0.0002 (our Moon’s is a distinctly wonky 0.05, and Pluto’s eccentricity with regard to the Sun is a positively inebriated 0.25). So the distance of Charon from Pluto can therefore be said to be the same all the time if you round to the nearest kilometre, 17,536. On Pluto there would be no media frenzy for the next “Super Charon”).
Charon is named after the ferryman who the Greeks needed to pay to take their dead to the underworld (ruled by Hades, or Pluto to the Romans). Charon was one of the old “primordial” gods of Greek mythology. His father, Erebus, was the personification of darkness, which probably gave him a head start for landing a job in the underworld.
English mathematician and theoretical astronomer John Couch Adams was born on June 5th, 1819, near Launceston, in Cornwall. Under the guidance of his maternal uncle, the Rev. John Couch Grylls, and using the facilities of the Mechanics’ Institute, Devonport, to further his studies privately, at the age of 2o he entered St. John’s College, Cambridge. He excelled at mathematics to the point of achieving the exalted position of Senior Wrangler (nothing to do with cows or denim, it’s the top scoring maths graduate of the year) in 1843.
Two years previously he had already begun to be intrigued by the possibility of a planet beyond Uranus, as the following nineteenth century “note to self” shows:
“Formed a design . . . of investigating . . . the irregularities in the motion of Uranus, . . . in order to find whether they may be attributed to the action of an undiscovered planet beyond it . . . “
Adams’ study of the perturbations of Uranus’ motion first led him to conclude that an unknown planet beyond Uranus, located at double the distance from the Sun, might exert the necessary influence on Uranus if it was big enough, and in the right place. Following his obtaining more precise observations from the Astronomer Royal, a more refined prediction of how to locate the eighth planet was made, which Adams took to Greenwich Observatory and left for the attention of the aforementioned Astronomer Royal.
At the same time, Urban Le Verrier had also been on Neptune’s trail, and had predicted a location within one degree of that determined by Adams. Unfortunately for the reputation of British astronomy, the lack of accurate star charts meant that looking for an object moving against the background involved a painstaking wait for two lots of observations to be undertaken, recorded and compared. But Le Verrier’s calculations were in the hands of Dr Johann Galle at the Berlin Observatory and, despite beginning his search two months later than the British team (led by James Challis), with typical German efficiency he discovered the planet on the first night of observation, through the rather obvious method of having accurate star charts to hand.
1885 – Discovery of asteroid 248 Lameia by Johann Palisa. Lameia is a main belt asteroid of about 49 km diameter, of unknown spectral type. It’s strange that we can know some things about these rocks very precisely, and others not at all. For example, the JPL Small Body Database tells me that the orbital period (year) of 248 Lameia is 1418.21351670694 days. That’s quite precise.
Lameia takes its name from Greek mythology, as do most early asteroid discoveries. Lamia was a queen of Lybia who made the mistake of becoming one of Zeus’ lovers. The affair panned out in the usual fashion, with Zeus’ wife, Hera, finding out about it, and turning Lamia into a child-eating monster.
2002 – Discovery of trans-Neptunian object 50000 Quaoar. Potentially a dwarf planet (it has a diameter of about 1000 km, but more information on its mass is needed before a decision can be made) I’m mentioning it mainly because 50000 is a nice round number, and partly because Quaoar was the first TNO to be detected directly from Hubble Space Telescope images.
We have a cubewano today! It is Kuiper-belt object 19521Chaos, which was discovered by the Deep Ecliptic Survey on November 19th, 1998. Chaos is about 600 km in diameter, and may well be a dwarf planet, not much smaller than Ixion and Varuna. It orbits between a perihelion of about 40.9 AU and an aphelion of just under 50.6 AU, and spends more than 300 Earth years completing a single orbit of the Sun (or 1 Chaotian year, obviously).
1996 – Launch of space shuttle Columbia on mission STS-80 (19 days late). At 17 days and 15 hours this became the longest shuttle mission, and comprised commander Kenneth D Cockrell, pilot Kent V Rominger, and mission specialists F Story Musgrave, Thomas D Jones, and Tamara E Jernigan. Musgrave was on his sixth flight, a record at the time, and became the only person to fly all five shuttles.
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 Charonshould 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 Horizonsprobe, 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.
I couldn’t have planned it better myself. We start the New Year with 1 Ceres, the first asteroid to be discovered. Now designated a dwarf planet, Ceres was found by Giuseppe Piazzi on January 1st 1801, and announced to astronomers on January 24th, when he had made enough observations to be fairly sure of what it was. Its existence had been suggested by Johann Elert Bode in 1772, and the space where a planet ought to be was first mentioned by Kepler as long ago as 1597.
Ceres is enormous when compared to most of the other members of the main asteroid belt that we will be encountering over the following twelve months, measuring nearly 1000 km in diameter at the equator (about 60 km less if you measure through the poles). It is far and away the largest asteroid in the main belt, and accounts for about a third of the total mass. Despite this, Ceres is still too faint to be seen with the unaided eye.
Ceres is thought to be composed of a rocky core and icy mantle. Studies of the surface composition have tended toward the view of water ice, carbonates and iron-rich clays. It may also have a thin atmosphere.
The spacecraft DAWN has taken some great close-up shots of Ceres, including the following, taken on December 10th, 2015, from about 240 miles up (385 km) showing the area around a chain of craters, the Gerber Catena, in the southern hemisphere.
Another recent shot shows the impressive crater Occator, a feature about 60 miles (90 km) across, taken from much further out (about 2,700 miles (4,400 km). Don’t worry about the colours; Ceres isn’t blue. The colour scheme is a device for studying surface composition. Occator contains one of the five brightest areas spotted on Ceres.
The Roman deity Occator was god of the harrow (what you use to break up soil). He was heavily associated with Ceres, with good reason, because in Roman mythology the goddess Ceres was their equivalent of the Greek deity, Demeter, goddess of agriculture and grain crops (her name is almost certainly derived from the same root as the word “cereal”). Ceres was considered important enough to have a seven day festival in her honour each April, called the cerealia, including theatrical performances and a horse race in the Circus Maximus. On a slightly less savory note, a nighttime ritual of the cerealia involved tying lighted torches to the tails of foxes and releasing them into the Circus Maximus.
Today’s non-astronomical photograph is of a sculpture in the garden of the Schönbrunn Palace, Vienna, former residence of Emperor Franz Joseph.