Planet X Larger Than Pluto?

The Minor Planet mailing list is buzzing with the discovery by an amateur astronomer of a 17th magnitude object 51 astronomical units from the Sun, tentatively designated 2003 EL61. For those not versed in astronomical lingo, this is an object several times brighter than Pluto even though it is 25% farther out from the Sun (the orbit vizualised by JPL). This means that barring a strangely reflective surface, this object is larger than Pluto, possibly Mars-sized! The debate whether Pluto is a planet is likely to get rekindled by this discovery."