8 Planets Suffice

             

Barry Kellett

Barry Kellett of the Rutherford Appleton Lab* gave an informative and tightly-reasoned talk in the Cornerstone, Didcot about demotion of Pluto from Planet to mere Plutoid. 

His talk began with a concise history of our knowledge of the solar system starting, as one should, the ancient Greek and proceeding from Ptolemy, Copernicus, Galileo, Kepler, and Herschel to the discovery of Pluto by Tombaugh.

What I particularly liked about the exposition were the details, particularly the ironic nuances

of history: for example that the data that predicted the existence of a trans-Neptunian planet was later found to be inaccurate, making the discovery a coincidence; and the numerologically unsound but mysteriously predictive Bode's law. Kellett has a keen ear for a good story.

The demotion of Pluto by the IAU meeting in Prague on August 24th**, 2006 caused a fuss by interested parties at the time, but no-one argued on Tuesday for its re-instatement. Had it all been a storm in a space-cup? Maybe the attenders had forgotten the mnemonic: My Very Excellent Mother Just Served Us Nine Pizzas, in which the liberal Nine Pizzas must now be replaced by boring old Noodles.

Kellett gave cogent arguments for the non-inclusion of Pluto, but perhaps the most convincing were graphs*** showing how out of place Pluto was in the club of planets. But that's science— what about culture? If scientists tell us they don’t regard Pluto as a planet any more do we also have to fall in line? There is another broad-ranging debate waiting to happen there.

The talk was well-attended (over 60) and there were intelligent questions asked and answered about exoplanets and the possibility of locating a home from home on an earth-like planet about some other star, though how we would get there was a question left for another time.

* Space Physics Division, Space Science and Technology Department

** A Thursday

*** One of the indicators making this clear is the ratio of a prospective planet's mass to that of all

the other stuff within its own orbital ambit; Pluto

manages a mass ratio less than1, while the planets each 

manage values of well above 1,000. 

Earth manages 1,000,000.

18th October, 2011