Jupiter’s moon Pasiphae(known as 1908 CJ when first discovered, then Jupiter VIII)was first seen by human eyes on January 28th 1908. The eyes in question belonged to Philibert Jacques Melotte, a British astronomer, despite the name, and the actual discovery date goes down as the 27th rather than the 28th because that was when CJ was first photographed by the Royal Greenwich Observatory. It’s one of the retrograde satellites of Jupiter, and was eventually named after the mother of the Minotaur (a name with an “e” on the end, in the manner suggested by Jürgen Blunck to distinguish between Jupiter’s prograde and retrograde moons) after being informally known as Poseidon for a while.
There’s apparently no rush at the International Astronomical Union. The name Pasiphae was finally proposed by the “Working Group for Planetary System Nomenclature” at the same time as eight other Jovian moons, in October 1975, 67 years after discovery. It was then accepted by the IAU General Assembly the following August.
Pasiphae is a small moon by the standards of more well-known satellites at about 20km radius, but because of the enormous quantity of Jovian moons, most of which have radii in single figures, it’s actually one of the larger.
1904 – Asteroid 523 Ada discovered January 29th, 1904 by American astronomer Raymond S. Dugan. He named it after Ada Helme, a schoolfriend from Montague, Mass.
Luna 1 was launched by the USSR (Russia) on January 2nd 1959, and was intended to be the first spacecraft to impact the Moon. Unfortunately for the Soviet scientists involved in the program an error back on the ground caused the rocket carrying it to burn for too long, changing the trajectory and sending the payload hurtling past the target at about 6000 km distance. The result was that on January 4th 1959, Luna 1 entered a heliocentric (around the Sun) orbit between Earth and Mars, becoming, I suppose, the first artificial planet. It’s still up there, completing an orbit of the Sun every 450 days, and will probably remain there for a very long time.
Despite missing the target, Luna 1 did provide some useful information. It was able to measure the solar wind for the first time, and discovered that the Moon has no detectable magnetic field.
Our photograph today is of a replica of Luna 1, so you should probably ignore the huge stalk sticking out of the bottom.
1905 – Discovery of Jupiter’s eighth largest moon, Elara, by Charles Dillon Perrine. For some reason Elara didn’t receive its present name until 1975.
The Jovian moon Themisto, discovered on September 30th 1975 by Charles Kowal and Elizabeth Roemer, is a rather small, irregular moon, orbiting about halfway between Jupiter’s large, well known Galilean moons and the rather less famous Himalia Group of prograde irregular companions. The best photographs currently available on the Internet show Themisto as a white pinhead on a black background, so I haven’t bothered “borrowing” one.
Themisto was named after a character from Greek mythology, the subject of a tragedy by Euripides which has unfortunately been lost. In the play, Themisto accidentally kills her own children, believing them to be the offspring of her husband’s first wife. When she realises what has happened, Themisto does what the star of any tragedy would be expected to do, and kills herself as well. The Greek stage at an average drama festival was littered with more bodies than an entire season of Murder She Wrote.
Co-discoverer Elizabeth Roemer also has two asteroids to her name, the magnificently named 1930 Lucifer and 1983 Bok. Charles T Kowal does even better, with 19 minor planets discovered between 1970 and 1981, including 2060 Chiron, the first of the centaurs. His collection of astronomical trophies also boasts a few comets, and Leda, another Jovian satellite.
Amalthea, named after the foster-mother of Zeus, is Jupiter’s third moon (counting outwards), and the largest of the inner satellites. It was the last to be discovered by an astronomer standing staring up a telescope rather than taking photographs to peruse later. The astronomer was Edward Emerson Barnard (of Barnard’s Star fame) and he discovered Amalthea on September 9th 1892 with the 36 inch refractor at Lick Observatory in California.
Amalthea is roughly ellipsoidal in shape (a bit like a rugby ball), about 250 km long and 140 km wide, and orbits Jupiter with the long axis always pointing towards the planet (in the same was as our own Moon, known as tidal locking). It is mostly reddish in colour, but patches of green have been seen. The surface is widely cratered.
Amalthea would be a fantastic place from which to view Jupiter. The giant planet occupies 46° in the sky, or about a quarter of it. You would have to careful not to jump up and down with the excitement, though, as the escape velocity of 0.06km/s means that if you did jump up, the “and down” part wouldn’t happen.
The mythology side of today’s post is a little confused, because there are varying versions of Amalthea’s story. She doesn’t even assume human form in all of them, being instead a goat. Some stories have Zeus, after Amalthea’s death, using her skin as a protective aegis. So I’m hoping she was a goat, and not a nurse. That would be particularly unpleasant, even by Zeus’ standards.
ALSO TODAY: Asteroid 56 Melete discovered, 1857. Asteroid 61 Danaë discovered, 1860.
Asteroid 189 Phthia discovered, 1878. Asteroid297 Caecilia discovered, 1890. Asteroid 298 Baptistina discovered, 1890.
Juno, in Roman mythology, was the wife of Jupiter, king of the gods. She was apparently the only one of the immortals able to see through the clouds Jupiter was in the habit of using to conceal his unsavoury activities. This made the name a great choice for the Juno mission, launched August 5th, 2011, as part of the NASA New Frontiers program, to unlock the secrets of the origin and evolution of our largest planetary neighbour.
Juno’s mission parameters included measuring the amount of water Jupiter has in it’s atmosphere, mapping the magnetic field, exploring the Jovian aurorae, and peering through the atmosphere to study it’s temperature, composition and movements.
It was a long trip, ending in orbit around Jupiter on July 4th 2016. Originally in quite a lazy 53 day orbit, this was later shortened to one of 14 days for the primary science collection period.
The first of 36 orbital flybys was performed on August 27th of that year, with Juno skimming a mere 2,600 miles (4,200 km) above the gas giant (trust me – it sounds a long way away, but on Jupiter, that’s skimming).
Highlights of the mission have included
detection of a changing internal magnetic field (secular variation) which could help our understanding of Jupiter’s, and maybe earth’s, interior structure.
new images of volcanic plumes on Jupiter’s moon, Io.
Best resolution detection ever of “wave trains” of moving air in the upper atmosphere (these were originally spotted by the Voyager mission) possibly the visible result of some process happening further down in the atmosphere, beyond Juno’s ability to detect.
New insights into Jovian lightning, which it turns out is more common towards the poles (unlike Earth, where it tends to be more common nearer the equator).
Amazing photographs . . .
ALSO TODAY . . .
1930 — Birth of American astronaut, Neil Armstrong.
July 21st 1969 is going to take some beating as far as big days go. I’ve been thinking about it, and it’s just really obvious that nobody has ever done anything even remotely as impressive as walking on the Moon. The more one thinks about it, the less likely it seems that it was even possible with 1960′s technology (don’t forget that the processors used in the guidance system were smaller than the ones available in home computers just a decade later, and my android phone is obviously from a different planet).
Maybe something to top it will come along eventually (the first gay pope to visit Mars, maybe?) but in the meantime, here are a couple of other events being commemorated and largely forgotten in the enormous shadow thrown by Neil Armstrong’s boots.
1914 – Discovery of Jupiter’s moon Sinopeby S B Nicholson, while he was working as a summer assistant at Lick Observatory. The ninth satellite of Jupiter to be spotted, Sinope was, as I say, discovered in 1914, but didn’t receive a proper name until 1975; until then it was simply “Jupiter IX”. It was named, along with eight other moons, “on the recommendation of the Working Group for Planetary System Nomenclature” of the IAC. Nicholson’s discovery was slightly serendipitous, as he was actually photographing “Jupiter VIII” at the time with the 36-inch British-built Crossley Reflector, a device the observatory had bought from it’s previous owner when it became obvious that the skies above Halifax, England, were a waste of a large telescope.
1998 – RIP Alan Shepard. Shepard (another of the Mercury Seven) was, as commander of Apollo 14, the fifth man on the Moon, and the first to play golf there. It’s perhaps just as well that the Americans conquered the Moon. I doubt the effect would have been quite the same when the first Briton on the surface got his dartboard out.
1961 – Launch of MR-1, the first unmanned spacecraft of the Mercuryproject. A spectacular failure, it managed to attain an altitude of four inches in a flight lasting 2 seconds.
2006 – Discovery of Actaea, the satellite of trans-Neptunian object 120347 Salacia.
Adrastea, the second moon out from the “surface” of Jupiter,was discovered by analysis of Voyager 2 images in 1979 by David C Jewitt and G Edward Danielson. A subsequent photograph is available (the Voyager one was of a tiny speck) taken by the Galileo spacecraft, and here it is, looking more like an out-of-focus lemon than a moon . . . .
Adrastea is like the Earth’s Moon, in that it always keeps one face pointing towards the parent planet, but it has an unusual orbital period of 7 hours 9 minutes, which is about two hours less than one Jovian day, even though Jupiter has the fastest rotation of all the planets (which accounts for its easily visible bulge). Only a very few moons do this (three are known, the others being Metis and Mars’ moon Phobos). As I mentioned two days ago, we can tell without looking it up that Adrastea will have a prograde orbit, because it ends with an “a”.
Metis and Adrastea share another unusual fact in common. They orbit too close for comfort to their parent, meaning that at some point in the future they will impact the planet.
In Greek mythology, Adrasteia was the nymph who had to nurse Zeusand hide him from his father, Kronos. Her name means “inescapable”.
1695 – Death of Christian Huygens.
1959 – Launch of Explorer 6.
2011 – Final launch of shuttle Atlantis (flight number STS-135).
Lysithea, discovered today in 1938 by Seth B Nicholson at Mount Wilson, is the second smallest of the Himaliagroup of Jupiter‘s moons (the others being Himalia, Ledaand Elara). This small group of moons, all about 11 million km from Jupiter, are similar in appearance and behaviour, and are therefore thought to have a common origin, possibly a C- or D-class asteroid.
Lysithea is named after a daughter of Oceanus, and was one of Zeus’ many conquests. And apart from these scanty facts there is just about nothing else I can find out about her. Newly discovered Jovian moons are all now named after lovers of Jupiter (Zeus) and as a rule end in an ‘a’ or an ‘o’ if they are prograde (orbit in the same direction as the planet) or an ‘e’ if they are retrograde(orbit in the opposite direction to the planet).
Being a mere 18 km across, and 778 million km away, there are no great photographs of Lysithea available. I was tempted to draw a black square and put a single spot of white on it, but I resisted.