A Moon By Any Other Name

Did you ever wonder how newly discovered moons and new features on planets are named?

When Galileo first aimed a telescope at the Moon in 1610 he saw mountains that looked very much like Earthly mountains. Thus we have a the lunar Alps, Caucasus, and Appennes Mountains named after terrestrial mountain ranges. The vast dark lava-flooded areas he saw he mistook for vast seas (mare in Latin) and thus we have the Sea of Tranquility, where the first Apollo 11 astronauts walked on the Moon, the Sea of Serenity, the Bay of Rainbows (Sinus Iridium) and the huge impact remnant known as Ocean Procellarum - the Ocean of Storms.

Craters, however, and some other smaller features are named, on our Moon, after philosophers and scientists. For example, a most obvious crater on the side of the Moon that always faces us (the moon is tidally locked to rotate at its orbital rate) is the huge rayed crater Copernicus. It is so large that if you were standing on it you would not know that you were in a crater (the horizon on the moon is only two miles away and Copernicus is almost 300 miles in diameter). There is the crater named Tycho near the south lunar pole. It's rays lead to the impact crater Kepler - since Kepler, the first modern astronomer and the first to discover how the planets moved, used Tycho Brahe's observations to derive his three planetary laws of motion (so the rays sort of indicate Tycho sharing his data with Kepler).

Aristarchus is another small but obvious crater; the interior is made of the brightest material on the moon. Like Aristarchus himself (who lived in the 3rd Century B.C. and was the first to point out that the Sun was the center of the solar system) the crater, while having little impact on the surrounding Moon, shines more brightly than any other spot on the Moon. Socrates, Plato, Archimedes, Tsilkovsky, Pasteur, Kuiper are all crater names on the Moon along with other great ancient and modern philosophers and scientists. On the back side of the Moon, because Russia was the first to observe it (the first spacecraft to orbit the Moon) the largest maria (singular of mare) is the Sea of Moscow.

But what about feature on, for example, the planet Mercury? These are generally named after famous authors and composers. (By the way, the naming of the celestial bodies is the task of the naming committee of the International Astronomical Union; star names have been recently sold arbitrarily along with a picture of the star, but this questionable practice has never been recognized by the IAU and such names are never used by the professional astronomical community). Thus we have craters on Mercury named Tolstoy, we have Bach crater, and the Wagner Mountain range there. On Venus, with one exception (the Maxwell mountains named after the great 19th century physicist James Clerk Maxwell) all features are named for famous women. There we can find Sacagawea crater, Florence Nightingale rile, Cleopatra caldera, and the Frejya (the Norse lady whom the day of the week, Friday is also named after) Mountains.

As other examples, on Mars valley networks are generally named after rivers or other languages' names for Mars or planets--many ancient languages are used. For example there is Auqakuh Valley (Incan for "Mars"), Dzigai Valley (the name for "river" in Navajo), Nirgal Valley ("Mars" in Babylonian), and the Reull Valley (the word for "planet" in Gaelic).

Since Jupiter has no surface,(none of the gas giant planets do) there are no lasting impact craters to be found there, but the innermost large moon of Jupiter, named Io, is known to be the most volcanically active moon in the solar system with up to a dozen simultaneous volcanoes being seen spouting material hundreds of kilometers into space when a spacecraft last looked.

Such features on this moon are thus named after fire gods, such as Pele (the Hawaiian goddess of fire whose work is clearly evident on the big island of Hawaii which grows by about 30 acres each year), Loki (the trickster blacksmith of the Norse), Masubi (the Japanese god of fire), and Surt (the Icelandic volcano god). Large ringed features on the Jovian moon Callisto, for example, are often named after "heavens" such as Valhalla (the heaven of the Vikings), the largest impact crater in the solar system or Adlinda, the place deep in the ocean where souls go in the Inuit mythology.

Skipping around, we find that the largest rings of Saturn are named A, B, and C for asymmetric, bright, and crepe rings (clearly planetary scientists were not expecting the thousands of rings found there by the Voyager spacecraft). However, the dubious pleasure of having gaps (clearings in the rings) named after one goes to Cassini (the Cassini division is a gap in between the A and B ring), Maxwell (he also figured out the nature of the rings), and Keeler--the first director of Lick observatory in San Jose, California, who observationally proved that the inner rings indeed rotated faster than the outer rings (i.e., the rings were really particles in orbit around Saturn).

As other examples, many features on Saturn's moon Mimas are named after characters in King Arthur's court. We have Galahad, Lancelot , Kay, and Guenevere craters there. The features on the moon Enceladus are largely named after characters in the Arabian Nights. Thus we have Aladdin, Ali Baba, and Sinbad, as well as Shaharazad crater. Until the Voyager spacecraft's encounter with the Uranian system, moons there were named after Shakespearean fairies, but are now named after Shakespearean characters in general. It was in this regard that I had occasion to learn firsthand how moons are named.

I was an associate member of the Voyager imaging team during the 1986 first encounter with the Uranian planetary system. Before the encounter five Uranian moons were known, and 8 rings had been discovered by airborne astronomy. (The Kuiper airborne observatory had flown in the path of Uranus' motion watching a star pass behind the planet Uranus with an idea toward understanding, for example, the depth of its atmosphere, but had found the star flashing on and off on either side of the planet as well which was due to the ring material on either side).

A colleague of mine, Bruno Sicardy (of Observatoire de Paris) and I noticed that on a particular long exposure of the rings of Uranus taken by the Voyager spacecraft that one of the stars did not seem to be moving in the same direction as the others. "That's a new moon" we said, but our colleagues doubted this, indicating that it was probably one of the known moons or that perhaps we had mistaken its motion. With the help of navigation calculations done by Steve Synott at Jet Propulsion Laboratory (one of the navigation team), we obtained a prediction as to when the moon, if real, would be seen in any additional pictures coming in from the Voyager imaging system. If real, such images would appear again going across the field of view in the pictures being transmitted the very next morning. I got caught up in traffic early the next day, but when I got in folks on the Voyager Imaging Team greeted me with, "Congratulations! You've discovered a new moon!" Yippee! Bruno and I had discovered whole new tiny little world!

We called my brother, who was well acquainted with Shakespearean literature, and the decision for a suggested name rested between "Mab" and "Peaseblossom" both fairies from Shakespeare's "A Midsummer Nights Dream". We suggested the name "Peaseblossom" then, which was well received by the scientists on the Voyager imaging team. Ah, but a controversy arose about the names of the new Uranian moons when a congressman, a few weeks later, suggested that the newly discovered moons of Uranus be named after deceased astronauts --a suggestion that soon drew a reply from the then Soviet Union pointing out that naming them after deceased cosmonauts was equally valid. This, then, actually started a bit of an international scuffle! Thus no name was assigned to our little "Peaseblossom" for several years.

Finally the name "Bianca", a Shakespearean character from Taming of the Shrew, was quietly chosen by the IAU committee on naming moons and in the Smithsonian Institution in Washington D.C. you will see that the Voyager spacecraft is (really rightly so) credited with discovery of a little Uranian moon named "Bianca" about 20 kilometers across. Ah well, I still like the name "Peaseblossom" and nothing, to my knowledge, is yet named "Peaseblossom" in the heavens. However, Shakespeare is still a daily part of my life, as I have named the computer on my desk "Peaseblossom." It is there to remind me that Bruno and I were the first ever to know of a wholly new little world. And when I remember the thrill of that discovery, by any other name, it still smells as sweet.

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Contributing Writer

Laurance Doyle is a principal investigator for the Center for the Study of Life in the Universe at the SETI Institute, where he has been since 1987, and is a member of the NASA Kepler Mission Science Team. Doyle’s research has focused on the formation and detection of extrasolar planets. He has also theorized how patterns in animal communication, like those of social cetaceans, relate to humans.