211th planetish object discovered

The discovery of planets beyond our solar system apparently continues apace. The latest is the discovery, a paltry 10.5 light years away, of a “Jupiter-sized world” orbiting Epsilon Eridani (which Trekkies will know as the home system of Mr Spock).

But what I want to know is: How many of these cosmic johnnie-come-latelies actually fit the IAU’s newly formulated criteria for what constitutes a planet?

Well, none of them actually, since the IAU has deemed that a planet, by definition, is “a celestial body that is in orbit around the Sun” (GA26-5 1(a)).

But, okay, allowing the definition to stand mutatis mutandis for objects in other solar systems, the issue then becomes one of how many of those 211 objects satisfy the two other criteria for planethood, namely...

(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.

Given the limits of observation, one would think that further study of these objects would be required to settle those questions.

In the meantime, if astronomers want to refer to these planetish objects as ‘planets’, then the rest of us may be justified in continuing to refer to our beloved Pluto as our ninth planet.

As a final aside, it’s interesting that most of the so-called planets discovered beyond our solar system seem to be “Jupiter-sized”. Noting the recent demotion of Pluto to ‘dwarf planet’, one is tempted to ask: Do astronomers have some kind of unhealthy obsession about size?

UPDATE: Please Save Pluto petition currently has 1,165 signatures!

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