To: WSFAlist at keithlynch.net
Date: Mon, 15 Mar 2004 00:09:45 -0500
Subject: [WSFA] Re: possible tenth Solar planet
From: ronkean at juno.com
Reply-To: WSFA members <WSFAlist at keithlynch.net>

On Sun, 14 Mar 2004 19:13:40 -0800 (PST) Rich Lynch <rw_lynch at yahoo.com>
writes:
>
> Anything smaller than Pluto hardly deserves to be called a
> planet.  Pluto itself is the smallest planet in the Solar
> System, even smaller than our moon.
>

Even Pluto's status as a planet is not without controversy.  Percival
Lowell, who paid for the telescope used to find Pluto, and who paid the
salary of its discoverer (Clyde Tombaugh), was very eager to make history
by finding a ninth planet, so when Pluto was found, there was a vested
interest in it being a planet.

The Lowell Observatory's position, not surprisingly, is that Pluto is
really a planet  http://www.lowell.edu/users/buie/pluto/planet.html , but
even they admit that Pluto is the only planet in its class ('Icy'), the
other classes being Terrestrial and Jovian.

If Pluto is taken to be a planet, then the size threshold for being a
planet would be somewhere between the size of Pluto (2390 km), and Ceres
(950 km).  On that basis, Sedna at 2000 km might qualify as a planet.
There has now been discovered an asteroid larger than Ceres, asteroid
2001 KX76 at 1200 km diameter (or larger).

Gravity on the surface of Pluto would be 7% of Earth's; on Ceres 3% of
Earth's.  It will be interesting to see what consensus develops on
Sedna's planethood.

Ron Kean

.

.

________________________________________________________________