March 13 – Discovery of Uranus (1781)

Uranus (named after a primal Greek god of the sky, the son and husband of Gaia, and father of the Titans) was discovered on this day in 1781 by William Herschel. It’s the 7th furthest planet from the Sun, orbiting at approximately 2.8 billion km, and is often classed as an ice giant with Neptune, as well as being a gas giant. Uranus is the third largest planet by radius (about 25,000km, or 4 Earths), but only the fourth largest by mass (roughly 14 times as massive as Earth).

Uranus and rings (image credit: NASA).
Voyager 2 image of Uranus and rings (image credit: NASA).

As with the other giant planets, Uranus has a plentiful supply of moons (27 at the last count). The largest five are Oberon, Titania, Umbriel, Miranda and Ariel. None of the Uranian moons are particularly large, with the biggest, Titania, being less than half the size of our Moon. The naming convention for Uranian moons is that they are all characters from either the plays of Shakespeare or The Rape of the Lock by Alexander Pope. Most of the Shakespearean names were taken from The Tempest and A Midsummer Night’s Dream, but I suppose they started running out after a while, so nowadays anything goes.

Uranus also has a ring system. The rings, of which 13 are known, are dark, narrow, and probably quite young (less than 600 million years old). They are thought to be the remnants of one or more shattered moons. The rings can be clustered together in three groups: nine main rings, two dusty ones, and two outer rings, including the brightest, the ε (epsilon) ring.

The atmosphere of Uranus (by which I mean the outer layers) usually presents a blank face to watching humans, and the Voyager photographs painted a picture of a serene world. But recently (August 2014) a collection of enormous bright spots have been observed, showing that giant storms can sometimes flare up on the planet.

1980CALYPSO, one of the smaller of Saturn’s fifty-three named moons, was discovered on this day in 1980. It’s an irregularly-shaped Trojan, trailing 60 degrees behind the larger moon Tethys at the L5 Lagrangian point, something I’m still planning on writing a blog about (another Trojan, Telesto, occupies a position 60 degrees ahead of Tethys, called the L4). Calypso is named after a daughter of the Titans Oceanus and Tethys.

1969APOLLO 9, under the command of James McDivitt, splashed down in the North Atlantic on March 13th 1969, after just over 10 days in orbit.

1855 – Birth of Percival Lowell, proponent of Martian canals, and founder of the Lowell Observatory, one of the oldest in the United States.

Birthday Boy Percival Lowell at the massive 24
Birthday Boy Percival Lowell at the massive 24″ Reflector in the observatory which bears his name.

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.


September 23 – Discovery of Neptune (1846)

Officially, Neptune was discovered visually on September 23rd 1846 by Johann Galle, but its existence had been proposed by Alexis Bouvard years before, and its position was predicted by Urban Le Verrier on August 31st 1846, and by John Couch Adams a couple of days later.  James Challis at the University of Cambridge was also in the running, and observed Neptune twice before the discovery was announced, but failed to realise what was going on.  And Galileo had seen and noted Neptune himself, but even he had no idea what it was.

Neptune from Voyager 1 (image credit: NASA)
Neptune from Voyager 1 (image credit: NASA)

The first suggestion for a name for this new planet came from Galle, who thought Janus might be a good idea, after the two-faced Roman god of beginnings, from whom we get the name of the first month of the year.  Challis, no doubt anxious to make up for being beaten to the finishing tape, suggested Oceanus, whose children we have been meeting all year in these pages in the guise of asteroids.  Oceanus married his sister Tethys, and their children numbered at least three thousand, which, as they were immortal, might not have put as much of a strain on Tethys’ plumbing as I might imagine, because I have no idea how long it took them to complete their family.

Le Verrier was the first to suggest naming the new planet Neptune, the Roman god of the sea, and appropriately a brother of Jupiter and Pluto (he also suggested, modestly, Le Verrier, but this idea didn’t gain much support outside France).  The name is used almost universally, although as Neptune was the Roman equivalent to the Greek Poseidon, Greece is, as far as I’m aware, the only western country to use that name instead.

Neptune is a small giant (yes, I know what I just said).  It is 17 times more massive than Earth, but only about 5% as massive as Jupiter.  It is similar in composition to Uranus, and the two of them, while still coming under the “gas giant” umbrella, are sometimes also referred to as “ice giants”.

As with the other giants, Neptune has a ring system, but not one that’s going to be used as a backdrop to an episode of Star Trek anytime soon.  The rings are fairly thin, and few enough in number to have been named after some of the players in Neptune’s discovery (the Adams, Le Verrier, Lassell, Galle and Arago rings).

Neptune's Rings (image credit: NASA)
Neptune’s Rings (image credit: NASA)

At last count Neptune was known to have fourteen moons, all named after water deities.  I’ll just briefly mention that the biggest are Triton (way bigger than the rest at 2,700+ km diameter), Proteus, Nereid, Larissa, Galatea and Despina, but as all fourteen will probably be turning up in these pages over the next twelve months, we will leave it at that for now.

Just as an aside, it has been speculated that in the dim and distant past of the solar system there might have been a fifth gas giant, which was flung out of orbit by a strong gravitational kick from Jupiter or Saturn.

ALSO TODAY . . . .

1791  –  Birth, in Hamburg, of Johann Franz Encke, comet hunter, and expert at predicting when they were going to return. Encke also has a gap in Saturn’s rings named after him, in recognition of his observations of that planet.

June 02 – Launch of Mars Express

Mars Express, launched on this day in 2003, was the first visit to another planet by the European Space Agency (ESA). And, unlike many of the modern long-range voyagers mentioned in these pages, the name “Express” is there to denote speed; it is not a highly-convoluted acronym describing the mission.

Artist’s impression of Mars Explorer. (Credit: Spacecraft: ESA/ATG medialab; Mars: ESA/DLR/FU Berlin)

The journey to Mars began at the Baikonur Cosmodrome and ended six months and 23 days later in orbit around the red planet. With seven instruments on board, Mars Express was able to study just about all physical aspects of its new home, including geology, mineralogy and atmosphere.

Highlights of the mission have included the discovery of minerals which only form in the presence of liquid water, radar detection of subsurface water ice, the possible detection of methane in the atmosphere, and evidence for an ancient system of underground lakes.

Another impressive result was how close Mars Express managed to get to the larger of Mars’ two moons, Phobos. The image below was taken from 351 km, but closest approach was 67 km.

Phobos, photographed by Mars Express. (Image Credit: ESA/DLR/FU Berlin).

The Mars Express orbiter is still going strong, and is expected to remain in service until 2022. Which is more than can be said for the British component of the package, the Beagle 2 lander, which landed on the surface in an impact crater called Isidis Planitia on December 25th 2003, and was never heard from again. More than a decade later a camera on board NASA’s Mars Reconnaissance Orbiter spotted Beagle 2, and close inspection suggested that not all of Beagle’s solar panels deployed successfully.

Image from the HiRISE camera, interpreted as the missing British Beagle 2 lander. (Image credit as in photo).

There’s plenty more to read about this mission at the ESA Mars Express website.


1967 — The unmanned US probe Surveyor 1 landed on the Moon.

1998 — Launch of space shuttle Discovery mission STS-91, carrying the prototype AMS-01, the first of two Alpha Magnetic Spectrometer missions.