[meteorite-list] OT: HOW MANY PLANETS?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Aug 3 18:29:51 2005
Message-ID: <200508032228.j73MSuQ20318_at_zagami.jpl.nasa.gov>

> Brian Marsden, in the article below:
> <http://www.space.com/scienceastronomy/050802_planet_definition.html>
>
> is quoted as saying if the Stern definition of a planet
> were used (everything spherical that goes 'round its star
> and doesn't fusion inside), we'd have 24 planets.
> Marsden himself says, "The only sensible solution is
> to accept that the solar system contains the eight planets
> known a century or so ago," Marsden said via email, "and
> to add new members only if they are larger than, say, Mars
> -- or maybe even the Earth."

It will be interesting to see what the IAU finally decides upon.
I personally think the definition should take into account the
size and orbit, and the object should be relatively unique.

> My definition (everything spherical and bigger than
> Ceres that goes around the sun), by excluding the four
> large minor planets, would give us 20 planets.

My personal opinion is that the asteroids in the main asteroid
belt are not major planets. They can be easily excluded with
a minimum size specification.

> The IAU and astronomy generally have a dilemma,
> though. How can you say that the massive 2003UB313 is NOT
> a planet when the smaller Pluto IS?

I can think of two ways. I think the object orbit's should be
a factor in defining a planet. 2003 UB313 is inclined at 44 degrees,
so if you exclude object above 20 degrees inclination, then Pluto
would be in and 2003 UB313 is out.

Another way is just make Pluto an exception to the rule, and have
it retain its planetary status. We have precedences for this. A platypus
lays eggs, but is still considered a mammal. Europa and Asia
are considered separate continents even though they are a single
combined land mass.

Incidently, if you demote Pluto from being a planet, then the
definition for a planet becomes much easier. If you include
Pluto as a planet, then the definition is going to get
more complicated.

Ron Baalke
Received on Wed 03 Aug 2005 06:28:56 PM PDT