Thursday night carpe_noctum_93 and I went to a public lecture at the University of Minnesota. The speaker was Mike Brown, author of the excellent book How I Killed Pluto and Why It Had It Coming, and that was the topic of the lecture. He was informative, convincing, and very funny. It is easy to see why he received the Richard P. Feynman Award for Outstanding Teaching at Caltech. He spoke without notes. For someone who styles himself “killer” he seems extraordinarily likeable. The crowd was huge, completely filling the large lecture hall and an overflow room.

For a summary of the issue see Why Pluto is No Longer a Planet. One other important point is that planets have been demoted before. Ceres and some of the other asteroids were considered planets after their discovery in the early 19^th century, but have long since been reclassified as asteroids, and with many other objects make up the asteroid belt. I heard beamjockey make this point at Windycon in 2008. Similarly Pluto was the first object to be discovered in what we now know as the Kuiper belt. Many others have since been discovered, and Pluto is no longer alone, or even the largest body out there. That title now belongs to Eris, discovered by Brown and his team in 2005.

What has struck me about Brown’s arguing against Pluto’s status as a planet is what he is giving up. If Pluto is to be considered a major planet than Eris must be as well, which would Brown in the very select company of known planetary discovers (Mercury, Venus, Mars, Jupiter, and Saturn were all known as far back as we have records). Here is what the list would look like:

• Uranus: William Herschel
• Neptune: Urbain Le Verrier, Johann Galle, Heinrich Louis d’Arrest, and John Adams
• Pluto: Clyde Tombaugh
• Eris: Mike Brown

Seven people in all of history. However, he said that when people called him the discoverer of the 10^th planet he felt like a fraud. He knew all along that neither Eris nor Pluto should be considered major planets.

Some other references:

• Cosmic Definitions: What Is a Planet
• Meet the Solar System’s Dwarf Planets
• A Conversation With Pluto’s Killer: Q & A With Astronomer Mike Brown
• Free the dwarf planets!
• Planets X and Pluto. This is an older (1980) book, but it is an outstanding account of the discoveries in the outer solar system up until then, well before additional Kuiper Belt objects were discovered.

For ongoing information see Mike Brown’s blog and his Twitter account.