Satellite Imagination: Unnamed Moons

Galileo discovered the first satellites (except for our Moon) in the solar system. In the opener of the “satellite imagination” series, you get a piece of the story connected with that. You might think that moons half a billion miles away have little effect on the Earth. Speaking astrologically and gravitationally, you would be right. Yet those moons orbiting Jupiter shook the relationship between science and religion. It has remained in a sort of tension ever since. Occasionally it explodes like volcanoes on Io. Other times, one beholds a certain serenity, but who knows what scientist or religious person is really thinking under that crust of ice.

You might think there was a rush to name the satellites of other planets. But professional astronomy was, for the most part, apathetic. Roman numerals were enough for Jupiter’s satellites. American astronomers making discoveries didn’t really push the issue. In fact, some of them had more important things to consider: comets, star clusters, and galaxies. VI, VII, and VIII weren’t the most imaginative designations, but they were sufficient until the Space Age.

By the final decades of the nineteenth century, the baton of planetary astronomy had passed to American shores, at least as far as the discovery of natural satellites was concerned. Americans built big telescopes, and they started putting them on mountains. The Lick Observatory began operations in 1888, and six years later they scored a big find: Jupiter’s first moon in almost three centuries.

California’s Lick Observatory, above in 1900.

Ohio’s Charles Dillon Perrine heeded the call to “Go west!” As a young man he came to work at Lick Observatory a few years after it opened. He didn’t find his satellites by looking through the world’s largest refracting telescope. The infant art of photography was put to the service of the ancient science of astronomy, as it was when Saturn’s Phoebe was discovered in 1898.

In 1904/05, the discovery of new moons wasn’t big news like it was in 1609. Scientists had devoted more imagination to comets, who gave Comet Borrelly top billing over Jupiter’s unnamed 6th moon in Astronomical Journal‘s supplement #570.

We refer to this satellite by the name of Himalia, a nymph who bore three sons of Jupiter. Even Jupiter was more enamored of her, as the name didn’t become official till 1975. I guess when you name a comet for a discoverer, there’s more excitement than for mythological paramours.

You might think Jupiter VI (as it was known for seventy years) has gotten a snappy image from one of Earth’s passing space probes. Alas, this is the best we’ve done:

To the passing Cassini on its way to Saturn, Himalia wasn’t much. It might be round with a large crater or dark spot. Or it might be irregularly shaped–not unusual for a solar system body the size of Belgium or New Jersey. By the time you get to objects around a hundred miles across or smaller, there’s not enough gravity to hold them into a roundish shape. One asteroid is shaped just like a dog biscuit–I kid you not.

A month later Perrine followed up with the discovery of Jupiter VII. A lot is left to the imagination here, too, as our best image is from an earthbound telescope:

A.C.D. Crommelin, writing in 1905, wanted a little more imagination than Roman numerals:

Unfortunately the numeration of Jupiter’s satellites is now in precisely the same confusion as that of Saturn’s system was before the numbers were abandoned and names substituted. A similar course would seem to be advisable here; the designation V for the inner satellite was tolerated for a time, as it was considered to be in a class by itself; but it has now got companions, so that this subterfuge disappears. The substitution of names for numerals is certainly more poetic.

Scientists get a rep for being rational sorts. But as human beings, some astronomers dislike it when something throws a wrench into their clockwork universe. Both of Perrine’s new moons were orbiting at thirty-degree angles to the plane of the solar system and Jupiter’s other moons. Crommelin complained:

These new satellites are indeed impairing the symmetry of the solar system by the peculiarities of their orbits.

But at magnitudes 14.6 and 16.3, Himalia and Elara were among the dimmest moons yet discovered. Elara and Saturn’s Phoebe are about the same dimness as seen from Earth. Himalia is on a par with Pluto, even a little brighter. One might ask why dimmer objects are discovered sooner than brighter ones. Put simply, a planet could be anywhere. But moon hunters have an advantage over seekers of planets, comets, and asteroids, as the search is confined to the near regions of a planet. Himalia and Elara are each within two full moons of Jupiter, as seen from Earth.

Europe notched a find in 1908: Philibert Jacques Melotte detected Jupiter VIII while working at the Royal Greenwich Observatory. Despite his French-sounding name, Melotte was a Brit. His parents emigrated from Belgium. The discovery seems accidental, as Melotte’s specialty was deep-sky objects: nebulae, star clusters and galaxies. After a rash of satellite discoveries in the Americas, the Royal Astronomical Society was appreciate enough. They awarded Melotte a medal. In 1975, the moon itself was finally awarded a name: Pasiphaë.

Like Triton, moon of Neptune, Pasiphaë orbits retrograde, or backwards around its planet. Like Charles Perrine’s discoveries earlier in the decade, this moon also is inclined about thirty degrees from the orbital plane of Jupiter’s large moons. And because it orbits so far from the planet, about 16 million miles on average, the sun tugs at the forty-mile-wide body, which means it orbits a little differently each time around the big planet.

Next up in the series, more discoveries at Jupiter get kicked off by a grad student. Eventually the king of the planets surpasses Saturn for known satellites.

About catholicsensibility

Todd lives in Minnesota, serving a Catholic parish as a lay minister.
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