Ceres, dwarf planet

As widely reported, on 24 August 2006 the IAU defined planets and other bodies in our Solar System into three distinct categories. The resolution reads in part:

(1) A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

Under the new definition Ceres becomes one of three "dwarf planets", the others being Pluto and the yet to be named 2003UB313 ("Xena"). Lost in the shuffle seemingly is the possibility of double planets. As I read it, the definition applies only to our Solar System and thus totally sidesteps the question of exo-planets and rogue planets.

Fifth Planet

Under a proposal before the IAU, a formal definition of planet is to be voted on. Very briefly the proposal sets forth criteria which touch on orbital and dimensional characteristics of non stars. The motivation for considering the proposal has been the discovery of Pluto like objects outside of the orbit of Neptune. While the deep space Kuiper Belt bodies brought on the debate, the solution could bring the Asteroid Ceres back into the fold of the planets in our Solar System.

Ceres was considered to be a planet after its discovery for most of the 19th Century. At the time it seemed to fit a hole in "Bode's Law" on orbital spacing of the planets. The discovery of other objects in similar orbits and the inability to resolve a disc resulted in Ceres being reclassifed as a "little star" (i.e. asteroid). Bode's Law is no longer seen as a physical law, but more of a quirk. Similarly, Pluto, isn't the "Planet X" that astronomers were looking for in the 1920's.

Today we know that Ceres has something like a third of the total estimated mass of the main belt. Hubble Space Telescope images of Ceres show it to be round, and Ceres is thought to have a differentiated interior and possibly an atmosphere. All of this makes it far more of a standout among "asteroids" than Pluto/Charon appear to be among Kuiper Belt bodies. (note that I'm not saying Pluto doesn't also have some of these features.) Ceres' orbit is whole lot more regular than the Kuiper belt bodies. And though I would have prefered to wait until the Dawn probe confirmed (or killed) some of the speculation about Ceres, I find it no harder to call Ceres a "planet" than Pluto/Charon or 2003UB313.

The IAU proposal at least provides objective criteria for designation as a Planet which don't appear, at first blush, to be completely arbitrary. I would agree that the draft proposal was influenced by a desire to "save" Pluto's designation, but having done so, it was almost impossible to avoid sweeping in Ceres without looking like the desired result was controlling the selection of criteria. If orbital criteria (e.g. dominant body among those in similar orbits, etc) had been added to the proposal it would have easier to write off Pluto than Ceres.

Just a thought

An old shot of Saturn's largest moon.

Indiana Gov. Daniels has lately concluded his popularity could only be enhanced by becoming our "education" governor and is now pushing for full day kindergarten. But, as is so typical of him, he has conjured a way that allows most Hoosiers to pretend it won't cost them anything. He proposes increasing the cigarette tax to fund the program.

In the last General Assembly he gave us "Major Moves", basically a sale of the Toll Road to raise money for a statewide road building spree. He repeatedly said that the the money coming from the Toll Road sale was the equivalent of a "winning powerball ticket" or something to that effect. Something for nothing in other words. Financing this “lottery ticket” was left to the northern tier of counties, particularly those tied to Chicago’s economy, who in reality will foot the bill for the next 75 years. Now he has gone one better. Smokers will finance kindergarten and it will be for their own good (its unhealthy anyway). This is obvious moral posturing and targeting of an unpopular minority. One might observe that smoking declines with income so this bill is be presented to lower income Hoosiers. Ought to play well in Hamilton County.

One wonders though what happens should they stop smoking.

Daniels’ play is pure demagoguery, but smooth.