February 18 – Discovery of the “Planet” Pluto (1930)

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.

Pluto from the New Horizons probe (image credit: NASA/APL/SwRI)
Pluto from the New Horizons probe (image credit: NASA/APL/SwRI)

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.

Pluto and Charon (image: NASA)
Pluto and Charon, pre-New Horizons (image: NASA)

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).

Surface detail of Pluto from New Horizons (image credit: NASA)
Surface detail of Pluto from New Horizons (image credit: NASA)

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.

A Selection of KBOs (image: NASA)
A Selection of KBOs (image: NASA)

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.

January 05 – Discovery of Eris (2005)

Dwarf planet Eris is the largest known member of a collection of objects known as the scattered disc, a subset of the larger group, the trans-Neptunian objects (TNOs).  It was discovered by a team from Palomar Observatory on January 5th 2005, and was given the “minor planet designation” of 136199.  Eris has a larger mass than Pluto by about 27% (and was partly responsible for the reclassification of Pluto by the IAU as a dwarf planet), making it the ninth most massive object orbiting the Sun.

Eris - Troublemaker
Eris – Troublemaker

Eris, and its moon Dysnonia, are a very long way away.  They orbit in a wild ellipse ranging from 38 to 97 AU from the Sun (about three times farther away than Pluto).

Eris has an appropriate name.  In Greek mythology she was the goddess of chaos and discord.  Inhabitants of Pluto, if they exist, would surely agree.

1969  –  Launch of the USSR’s Venus atmospheric probe Venera 5 from Baikonur Cosmodrome in Kazakhstan.  It reached its target on May 16th, and sent back data for almost an hour while descending by parachute through the Venusian atmosphere.


June 22 – Discovery of Pluto’s Moon, Charon (1978)

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.


True colour image of Charon (Image credit: NASA New Horizons).

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 up close (image credit: NASA New Horizons).

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”).

Pluto and Charon from just under 4 million miles (6m km). Image:NASA New Horizons

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.

Caron and some guests, as depicted by Ukrainian artist Alexander Dmitrievich Litovchenko



March 31 – 40 Harmonia

Main-belt asteroid 40 Harmonia was discovered by Hermann Goldschmidt on March 31st, 1856.  It is an S-type main belt asteroid, about 107 km in diameter.  One of 14 asteroids discovered by Goldschmidt, Harmonia is named after the Greek goddess of (obviously) harmony.  Her Roman counterpart was Concordia (who also has an asteroid named after her, discovered in 1860).  The name was chosen to mark the end of the Crimean War, which officially came to an end, with the signing of the Treaty of Paris, on the day before Harmonia was discovered.

Despite her harmonious attributes, the most popular stories surrounding this goddess involve a necklace she received on her wedding day, possibly from Hephaestus (different sources give various donors).  This necklace, while it apears to have had no adverse impact on Harmonia herself, had a long life bringing misery and death to all who owned it after her.

Polynices giving Eriphyle the necklace of Harmonia.
Polynices giving Eriphyle the necklace of Harmonia.

The photograph shows a red figure oinochoe (wine jug) by the Mannheim painter.   Eriphyle is being bribed by Polynices to get her husband Amphiaraüs to become embroiled in the battle of the “Seven Against Thebes”.  She was later to do the same to her son, Alcmaeon.  When he found out what she’d been up to, he killed her.

1886  –  Asteroid 254 Augusta was discovered by Austrian astronomer Johann Palisa on March 31st 1886.  It is a small main belt asteroid of about 12km diameter, and is of spectral type “S”.  It was named after Auguste von Littrow,  the widow of astronomer Carl Ludwig von Littrow.

1886  –  Asteroid 255 Oppavia is another main belt asteroid, and was also discovered on March 31st 1886 by Johann Palisa.  It’s rather larger than Augusta, at 57 km wide, and is a P-type.

The Arms of Opava
The Arms of Opava

Opava is the name of the town where Palisa was born.  It is currently in the Czech Republic, but at the time of Palisa’s birth it was part of the territory known as Austrian Silesia (following the War of Austrian Succession) which is why he is an Austrian astronomer.  Opava’s most famous daughter is Joy Adamson, author of “Born Free”.

2005  –  The large trans-Neptunian object (TNO) and Kuiper Belt object (KBO) Makemake was discovered nine years ago today.  As well as being as TNO, Makemake’s size allows it to bask in the title “dwarf planet”, and while various studies give varying opinions regarding the precise extent of that size, the prevailing view seems to be that it’s around 1,400 to 1500 km in diameter.  Unfortunately for early planet hunters, though, it’s also a very long way away,  (magnitude 16.7 at opposition) and has an unusually high orbital inclination, which is why it was only discovered so recently.

Spectral analysis of the surface suggest that up to 90% is covered in ices of methane and Nitrogen, with “tholins” also present, giving Makemake a reddish appearance visually.  It has almost no atmosphere, and (unusually for such a large TNO) no satellites.

1891  –  Discovery of asteroid 308 Polyxo by Alphonse Borrelly. Measuring 130 km across, Polyxo is one of the rare, mysterious T-type asteroids. There are multiple Polyxo’s in Greek mythology, but I believe this particular asteroid was named after one of the Hyades.

1997  –  Death of Lyman Strong Spitzer Jr.