Observatory Logo


From: TerryMoselaol.com
Date: Sun, 14 Mar 2004 12:31:13 EST
Subject: New Planet = bigger SS, Sunspot Image

Hi all,

1. The Solar System is now 2 billion miles bigger in diameter than we 
thought!  A new planet, discovered by Michael Brown & his team at Caltech, 
provisionally named Sedna (the Inuit goddess of the sea) orbits about 2 billion miles 
further out than Pluto. Is it a planet, I hear you ask? Well, it's only slightly 
smaller than Pluto, and quite a bit bigger than the other Trans-Plutonian 
objects in the Edgeworth-Kuiper Belt (EKBO's|). The official announcement will be 
tomorrow. 
   In 2002 Brown's team discovered "Quaoar", about 800 miles across, and 
orbiting 1 billion miles beyond Pluto. (Pluto's mean distance from the Sun is 3.6 
billion miles). Then last month they reported the discoverey of another body, 
provisionally named 2004DW, which is 10% larger, and slightly further away. 
These are the biggest of the 800 or son EKBOs, most of which are are about 
60-100 miles across.
   Sedna is thought to be about 1,200 miles in diameter, compared with 
Pluto's 1520 mile diameter. It's the biggest object discovered in the Solar system 
since Pluto 74 years ago; it's 50% bigger than Quaoar.
   Some astronomers want to re-classify Pluto from being a planet to being a 
large EKBO, but the majority voted to retain its planetary status.
   So is Sedna a planet or not? I always thought that the totally arbitrary 
figure of 1000 miles would be a reasonable dividing line between a planet & 
either an asteroid or an EKBO. It's a nice round figure, which I'm partial to, 
even if it is in the old imperial units! So I'll regard it as a planet until 
there's an official designation otherwise!

And sometimes tradition is as good a guide in these matters as anything - 
after all, we still refer to 'Planetary Nebulae', although they have nothing to 
do with planets! And we still retain the original constellations, with their 
weird boundaries (we even have one, Serpens, which is divided in two by another 
constellation, Ophiuchus!). So if we can put up with those anomalies, surely 
we can at least keep Pluto as a planet, even if Sedna is eventually classified 
as an EKBO!

2. IAA member Peter Paice's excellent new solar images are now featured on 
today's Spaceweather.com website.

BT, don't forget the IAA meeting, Stranmillis College, 7.30 on Tues evening, 
and the lecture in St Patrick's Trian, Armagh, on Wed night - see last email 
for details.

Clear Skies,

Terry Moseley 


Last Revised: 2004 March 15th
WWW contact: webmaster@arm.ac.uk
Go to HOME Page Home Page