Ceres–Either the Most or Second-Most Popular Dwarf Planet

It has been nearly a decade since the International Astronomical Union (IAU) formally defined the word ‘planet’, resulting in the reclassification of Pluto as a ‘dwarf planet’. Some people still remain upset about the decision, considering the new classification as a demotion. If you roll with the kinds of people that I do, battle-lines have been drawn around the issue and many a friendship have been lost in the process. I don’t want to rekindle those debates (this is likely inevitable, however, as Pluto will be in the news quite a bit in the coming months as New Horizons is finally about to have its encounter with the dwa… whatever-you-want-to-call-it), so let’s take a look at a dwarf planet that appears to have finally found comfort in its classification: Ceres.

Color view of Ceres as imaged by Hubble in 2004 - Credit: NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), L. McFadden (University of Maryland, College Park), and M. Mutchler and Z. Levay (STScI)

Color view of Ceres as imaged by Hubble in 2004 – Credit: NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), L. McFadden (University of Maryland, College Park), and M. Mutchler and Z. Levay (STScI)

If you thought Pluto’s designation was complicated and controversial, just wait until you Ceres’s story.

Ceres has had a bit of an identity crisis of its own. Italian astronomer Giuseppe Piazzi discovered Ceres on New Years Day, 1801. He at first thought it was a star, but observed its movements against the stellar backdrop over the course of a few days and determined it to be a planet. He took a conservative approach in his announcement however, by referring to it as a comet.

I have announced this star as a comet, but since it shows no nebulosity, and moreover, since it had a slow and rather uniform motion, I surmise that it could be something better than a comet. However, I would not by any means advance publicly this conjecture. – Giuseppe Piazzi in a letter to fellow Italian astronomer Barnaba Oriani

With the help of other astronomers and using a method for calculating orbits developed by Carl Friedrich Gauss, it was confirmed that the object was not a comet, but in fact some sort of small planet. German astronomer Johann Bode had been promoting his hypothesis that planets orbited their host stars at distances that could predicted by mathematics. This hypothesis predicted a planet should exist between Mars and Jupiter. When Bode heard news of Piazzi’s discovery of an object at precisely that location, he rushed to announce that the missing planet had been located and even went as far as to name it himself. The name he gave: Juno. Piazzi, however, had taken the liberty as the new planet’s discoverer to give it the name ‘Ceres Ferdinandea’, honoring the patron goddess of Sicily and King Ferdinand of Bourbon. Piazzi rightfully objected to Bode’s stake on naming rights:

“If the Germans think they have the right to name somebody else’s discoveries they can call my new star the way they like: as for me I will always keep it the name of Cerere and I will be very obliged if you and your colleagues will do the same.” Piazzi in a letter to prominent astronomer and editor of scientific journals, Franz Xaver von Zach.

Piazzi’s name ultimately won out, though it was shortened to its currently-accepted name: Ceres.

"Giuseppe Piazzi" by F. Bordiga - Image from Smithsonian Institute Library

“Giuseppe Piazzi” by F. Bordiga – Image from Smithsonian Institute Library

After more objects were discovered orbiting in the same area, Sir William Herschel, in 1802, labeled these new objects, including Ceres, as asteroids (though the term asteroid, which means “star-like”, wasn’t commonly accepted until the early 1900s).

So thus, Ceres became the first, and largest, of the asteroids that orbit between Mars and Jupiter in a loose collection that we collectively refer to as the asteroid belt. But Ceres’s identity crisis wasn’t over just yet. Ceres was king of the asteroids until 2006, when that controversial IAU reclassified it as a dwarf planet. 1

From star, to comet, to planet, to asteroid, and finally to dwarf planet, Ceres looks to Pluto and remarks, “Psh… and you think you had it bad.”

Now that this introduction is out of the way, stay tuned for more information about Ceres. I’ll tell you about this fascinating world and get you up to speed on NASA’s Dawn spacecraft that will be arriving at Ceres in March of this year.

Animation of Ceres as viewed by the Dawn spacecraft on January 13, 2015. - Source: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

Animation of Ceres as viewed by the Dawn spacecraft on January 13, 2015. – Source: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

(Much of the information in this post came from Giuseppe Piazzi and the Discovery of Ceres, G. Foderà Serio, A. Manara, and P. Sicoli, published in Asteroids III by the University of Arizona Press)


  1. Since Pluto’s reclassification from planet to dwarf planet was viewed by many as a demotion, I wonder if it’s safe to refer to Ceres’s reclassification from asteroid to dwarf planet as a promotion.