A breaking news story reports that NASA will be holding a press conference on Monday March 15th all about a new object (nearly the size of Pluto) which was first observed using the 48-inch Samuel Oschin Telescope at Caltech's Palomar Observatory.  Later images were taken by the Spitzer Space Telescope, Hubble and other telescopes around the world. 

Very appropriate news as our speaker at the March meeting last Friday (12th) was Dr Luisa Rebull from the Spitzer project. 

The news story at the BBC site has more information.  Also the original notice from NASA announcing the press release scheduled for Monday at 1pm EST.

Both the Spitzer and the Hubble have imaged the new object and it appears to be slightly smaller than Pluto and currently it is about 1.8 billion miles further out in the Kuiper Belt.  It's orbit is very highly eliptical and it takes 10,500 years to complete an orbit around the Sun.

The Spitzer was used specifically to detect the heat signature from the object.  The lack of heat recorded by the Spitzer was used to estimate the size to be no more than 1,100 miles in diameter (Pluto is 1,400 miles).  

More detailed news from NASA

This will surely re-ignite the "Pluto/Is it a Planet?" debate.  Now added to that will be... is this new object a planet?

UPDATE

Please be advised that many of the detailed elements of the story are being inaccurately represented by the media.  Dr Luisa Rebull from CALTECH suggested the following link for the most accurate and detailed information (created by one of the discoverers)