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 19 – Launch of New Horizons (2006)

We have two quick asteroids to start us off today.  Asteroid 502 Sigune was discovered on January 19th 1903 by old hand Max Wolf at Königstuhl Observatory near Heidelberg.  On the same day, young whippersnapper Raymond Smith Dugan, also working at Heidelberg, discovered the second asteroid of his career, 503 Evelyn (named after his mother).


On January 19th 2006, NASA launched the New Horizons probe to Pluto, so long ago it was still a planet at the time (and always will be for some of us).  I clearly remember thinking back then that it was going to take such a long time to arrive that I’d probably have forgotten all about it, but here we are more than a decade later and the visit is now on the cusp of becoming a fond and fading memory.

New Horizons (image credit: NASA)
New Horizons (image credit: NASA)

New Horizons was a fairly large program by today’s standards, costing about $650m, which sounds expensive, but it’s actually only about $5 per US taxpayer, and spread over the 15 years of the project it’s a mere 33 cents a year: a bargain!  The mission has also visited Jupiter, and once Pluto had been passed there was a rendezvous with a Kuiper Belt Object in 2019.  The object chosen didn’t have a particularly catchy name at the time (2014 MU69), and was apparently also known in New Horizons circles as PT1 (and yes, it did stand for “Potential Target”).  PT1 later got the nickname Ultima Thule (it’s two planetesimals stuck together with one name each) but is now officially named 486958 Arrokoth.  From a typing point of view I think I prefer PT1.

The Jupiter flyby, as well as being a scientific mission in its own right, and a useful testing-ground for the instrumentation before an extended period of hibernation for the long journey to Pluto, was used to increase the speed of New Horizons by “gravity assist” to 9,000 miles per hour.  I think I’ll have to get myself one.  At that speed I could travel across the Atlantic to visit my friend Joanne in Arizona in about 20 minutes.

During the visit to Jupiter, New Horizons imaged the moon Callisto, and studied Jupiter’s ring system, magnetosphere, and the atmospheric conditions on the planet.

Calisto from New Horizons (image credit: NASA)
Calisto from New Horizons (image credit: NASA)

Scientific instruments on New Horizons are under the command of the Clyde Tombaugh Science Operations Centre in Colorado, and a small quantity of the ashes of the centre’s namesake, the man who discovered Pluto in February 1930, have been sent along for the ride.  Tombaugh died on January 17th 1997.

Imaging of Pluto using New Horizons LORRI imager began in January 2015. Hundreds of photographs were taken of the Pluto system, enabling navigators to fine tune Pluto’s exact position, and calculate the precise distance between New Horizons and its target.

And at the time we thought these images were pretty impressive; but they were nothing compared to what we got when the Pluto system was finally reached.

 

Pluto from the New Horizons probe (image credit: NASA/APL/SwRI)
Pluto from the New Horizons probe (image credit: NASA/APL/SwRI)
Surface detail of Pluto from New Horizons (image credit: NASA)
Surface detail of Pluto from New Horizons (image credit: NASA)
Pluto (image: NASA)
Pluto (image: NASA)
Charon (image: NASA)
Charon (image: NASA)
Nix (image: NASA)
Nix (image: NASA)

See what I mean?


1747Birth of Johann Elert Bode in Hamburg. The “law” named after Bode uses a formula to predict the distances of the planets from the Sun. It’s great for the first six, and was hailed a success when Uranus (a name suggested by Bode) was found in the right place. Unfortunately, the existence of the asteroid belt and Neptune were not part of the plan. Bode has a comet, an asteroid (998 Bodea) and a galaxy (M81, Bode’s Galaxy) named after him (though I suspect any inhabitants of M81 might disagree).


1965Launch of Gemini 2 from Cape Canaveral. This was an unmanned flight, but it did include a practice ingress (clambering in) and egress (being pulled out) by crewmembers of Gemini 3. Following two occasions on which the launch assembly had to be dismantled (for hurricanes Cleo and Dora) and an aborted launch on December 9th, 1964, the eighteen minute flight took place on the morning of January 19th, 1965, and was only slightly inconvenienced by a power outage at Mission Control caused by the electricity demands of the television coverage.


 

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.


 

January 01 – Discovery of Dwarf Planet Ceres (1801)

Happy New Year.

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 from the DAWN spacecraft (image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
Ceres from the DAWN spacecraft (image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Ceres is enormous when compared to most of the other members of the main asteroid belt, measuring nearly 1000 km in diameter at the equator (about 60 km less if you measure through the poles), and accounts for about a third of the total mass of the belt. 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.

Ceres: the area around Gerber Catena (Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
Ceres: the area around Gerber Catena (Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

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.

Occator, Ceres, from DAWN (image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
Occator, Ceres, from DAWN (image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

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.

Ceres
Ceres

Today’s non-astronomical photograph is of a sculpture in the garden of the Schönbrunn Palace, Vienna, former residence of Emperor Franz Joseph.

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

 


 

June 05 – John Couch Adams

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.

John Couch Adams
John Couch Adams

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.


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.


ALSO TODAY:
1980 – Launch of Soyuz T-2.