Pluto, Once and Future Planet

“I can’t find Pluto anywhere!” – words of a grade-schooler at Hayden Planetarium.

History Channel ran an interesting Pluto retrospective last night. Dr. Neil deGrasse Tyson is a frequent science and astrophysics master of ceremonies on TV science shows, and director of Manhattan’s Hayden Planetarium, among other accomplishments. Dr. Tyson gained popular notoriety by supporting demotion of Pluto to “dwarf planet” status (2006), and, as planetarium director, being one of the first to remove the 9th “planet” from the gargantuan solar system exhibit.

Dr. Tyson back-pedaled a bit. The “definition” of celestial objects has changed radically over the centuries as new data are discovered, it’s changing now, and will change again and again in the future. To most of us, Pluto remains a “planet”, no matter what they say. Nobody cares that the “10th” dwarf planet, Quaoar, is actually bigger than Pluto.

What’s all the flap about?

Original Tombaugh plates - 1930 discovery of Pluto

Reviewing the arguments,

  • It’s tiny – smaller than Earth’s Moon
  • But it does orbit the Sun (elliptically)
  • But it is round, and it has not just one moon, but several.
  • But it’s in the Kuiper Belt, and doesn’t have the gravitational oomph to carve a clear-path orbit for itself amidst all that orbiting space debris.

Lost Continent of Atlantis

Here’s another case of “everybody’s heard about it, but nobody knows what it is”.The legend or myth of Atlantis goes back at least as far as Plato, who wrote of an earlier civilization which would date to about 9600 BC by modern accounting, if it existed at all.

In our little thought experiment, suppose for a moment scientists and scholars were somehow able to agree that such a land actually existed at the site of the destroyed supervolcano island Santorini (the Wikipedia article includes a dramatic satellite photograph that’s food for thought. We also posted our own article about the site in My Notes).

The thought experiment goes like this: if Atlantis were actually the original island Santorini, before it was blasted into the stratosphere, was Atlantis ever really lost?

Or, was it redefined?

Clyde Tombaugh discovered Pluto in 1930, putting to bed astronomy’s mathematical speculation about a mysterious “Planet X”.

We’re going to Pluto in 2015 – at least, that’s when NASA’s unmanned New Horizon spacecraft should arrive there. New Horizons has already passed Jupiter. And, astronomers have discovered over 473 confirmed “exoplanet” detections – planets orbiting other stars in the Milky Way. As equipment and technique continues to improve, new data is pouring in almost daily.

This new data will ultimately redefine how we look at “planets”, and, probably, how we define them.

“What’s in a name? That which we call a rose/By any other name would smell as sweet.”Romeo and Juliet | Act II, Scene II

In modern parlance, Pluto “is what it is”. The semantic lexicon of astrophysics does need to be redefined with expansion of the knowledge base, of course, but the objects being described don’t change a bit.

Who can forget the old kids’ mnemonic for the names and order of solar system planets?

Men very easily make jugs serve useful needs, period.


Chabot Space Science Center (Oakland, California)
Pluto, Wikipedia
Enough Already, Astronomy

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