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Naming Names Around Pluto

Centauri Dreams is told that one reason the name Pluto was chosen for the ninth planet in our Solar System is that the first two letters formed the initials of Percival Lowell. The Boston-born astronomer became world famous for his studies of the so-called ‘canals’ on Mars, but he devoted the last years of his life to the search for Planet X, a world he was convinced must exist. Dying in 1916, Lowell wasn’t around to celebrate Clyde Tombaugh’s discovery of Pluto some fourteen years later.

In my mind, names play a role not dissimilar from the collapse of the wave function in some versions of quantum mechanics. Perform an observation and from a superposition of states you get a hard data-point. In a similar way, give something a name (see Bradbury’s “The Naming of Names”) and you make a vaguely understood object or place concrete. We’ll get more concrete still with Pluto and its various moons when the New Horizons mission gets there and we start naming craters and peaks.

But we didn’t have to wait for New Horizons to name the two small Plutonian moons discovered last year. The International Astronomical Union has chosen the name Nyx for the inner satellite, an homage to the mother of Charon, Pluto’s largest moon. The outer moon is now named Hydra, a monster whose nine heads remind us of Pluto’s place within our system. And exercising just as much care as was originally applied to the naming of Pluto, the first letters of Nyx and Hydra honor the initials of New Horizons itself.

Pluto and its moons

Image: Hydra and Nix, roughly 5,000 times fainter than Pluto, are about two to three times as far from Pluto as its large moon, Charon. The brighter, outer small satellite, Hydra, was provisionally named S/2005 P 1, and the fainter, inner small satellite, Nix, was provisionally named S/2005 P 2. Credit: NASA/STScI.

“We’re very pleased with the decision of the IAU,” says co-leader of the discovery team and New Horizons principal investigator Dr. Alan Stern of Southwest Research Institute. “You’re going to be hearing a lot more about Nix and Hydra in coming years — astronomers are already applying for telescope time to study their orbits and physical properties. And when New Horizons flies by Pluto in the summer of 2015, each will be mapped in detail.”

Are more moons waiting for New Horizons to find? We’ll know by 2015, some 99 years after the death of Percival Lowell. Astronomy demands patience and an exquisite eye for detail, as Lowell surely knew from his long nights on the job, and it probably wouldn’t have surprised him that it would take almost half a century after the discovery of Pluto to find Charon, and another 27 years to locate Nyx and Hydra. The near resonant orbits of the latter two satellites in the same plane as Charon indicate a common origin for all three moons and back the notion that they were formed in an enormous impact.

Comments on this entry are closed.

  • Jose June 23, 2006, 13:12

    I understand the name was chosen by a young girl in the UK, the daughter of some academic. She was in the news a few months ago:


  • Jose June 23, 2006, 13:13

    Eureka, your comment section now works!

  • Administrator June 23, 2006, 14:04

    Still baffled about why it has always worked for some and never for others, but recent changes (thanks to your ideas and those of Paul at Velcro City Tourist Board) seem to have helped. Let’s hope this solves the problem.

  • Maastrichian June 23, 2006, 15:17

    I’m rather pleased with myself. Not long after the moons were discovered, myself and some friends speculated on eventual names (though we hadn’t expected any decisions for quite some time). One of my two guesses, Nyx, turned out to be spot on (minus the spelling, of course).

  • djlactin June 23, 2006, 22:56

    the name is ‘Nix’. ‘Nyx’ was nixed because it’s already the name of a near-earth asteroid.

  • Administrator June 24, 2006, 9:00

    djlactin is absolutely right. Correction goes in immediately.

  • Jose June 26, 2006, 16:32

    The problem wasn’t so much the commenting system as requiring users to be registered to Wordpress. Some of us have had difficulties getting the registration system to send us emails so we can complete the process.

  • José F. November 26, 2007, 23:24

    Now Pluto isn’t a Planet.! =/ is a dwarf planet!

  • ljk June 11, 2008, 14:28

    IAU Throws Pluto a Bone: “Plutoid”

    Written by Nancy Atkinson

    Almost two years after the International Astronomical Union (IAU) General Assembly demoted Pluto from a “real” planet to the new category of dwarf planets, the IAU, as promised, has decided on a name for trans-Neptunian dwarf planets similar to Pluto.

    The name “Plutoid” was proposed and accepted by the IAU at its recent meeting in Oslo, Norway.

    Here’s the definition of a Plutoid: “Celestial bodies in orbit around the Sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit.”

    Full article here:


  • ljk June 19, 2008, 17:01

    Pluto’s Identity Crisis Hits Classrooms and Bookstores

    By Jeanna Bryner

    Senior Writer

    Posted: 19 June 2008, 10:38 am ET

    NEW YORK — Pluto was once a planet. Then, a dwarf planet. And as of last week, a plutoid. The fall from grace has teachers, parents and educational publishers struggling to keep up, while kids remain loyal to their favorite, the ninth planet. Underscore planet.

    Last week, the International Astronomical Union (IAU) announced Pluto should now be called a “plutoid,” two years after the organization voted to demote Pluto to “dwarf planet” status.

    Meanwhile, many kids are nearly certain Pluto is still a planet.

    “I think it’s a planet. But me and my friends, we talk about it sometimes and we go back and forth,” said Natalie Browning, 9, sitting in a park in Manhattan with her family. “Right now, I’m not 100 percent. I’m just 75 percent” sure that Pluto is a planet.

    Natalie’s mom, Bobbie Browning, said, “You’ve got kids with textbooks saying that Pluto is part of the solar system and a planet, and teachers have to say it isn’t [a planet].”

    Science teachers and publishers already worked to update their resources to read “dwarf planet.” And now, boom, that category is out of favor among astronomers.

    “Students who have just learned about the concept of dwarf planets must now be taught the new concept of plutoid,” said Janis Milman, who teaches earth science at Thomas Stone High School in Maryland. “This will lead to confusion in the classroom and resistance to learning the new terms, because the students will question, why learn something that might change again in a year or so?”

    A cursory survey at a large chain bookstore here revealed three out of four books published in 2006 or later were updated, with Pluto designated as a dwarf planet and the solar system said to include just eight planets.

    Full article here:


  • ljk September 8, 2010, 22:12

    Sunday, September 5, 2010
    Mars: a world for exploration (1959)
    In 1929, Clyde Tombaugh joined the staff of Lowell Observatory in Flagstaff, Arizona, to hunt for Planet X, a world which Boston businessman Percival Lowell had predicted should exist beyond Neptune. On February 18, 1930, Tombaugh found Pluto.

    Although Pluto became Lowell Observatory’s most famous discovery, Percival Lowell had founded his observatory in 1894 to find proof of intelligent life on Mars. He had theorized that the planet was slowly losing its water, and that the dark lines some astronomers glimpsed on its ochre disk were canals its inhabitants had excavated to distribute meltwater from the polar ice caps and stave off encroaching deserts. Lowell had believed that spots strung like beads along the lines were oases, and that irregular dark-colored areas (maria) scattered over the surface were desiccated sea beds (bottom image above). Though rejected by most astronomers, Lowell’s romantic vision helped to inspire H. G. Wells’s novel The War of the Worlds (1898) and the “Barsoom” books of Edgar Rice Burroughs. These tales in turn inspired generations of rocketeers and skywatchers.

    In the January 1959 issue of Astronautics, the journal of the American Rocket Society, Tombaugh summarized the prevailing view of Mars’s surface conditions on the eve of its exploration by spacecraft. He first described three areas where improved data had undermined Lowell’s vision.

    Full article here: