On Friday, another definition, put forward by a group led by Julio Fernandez of the University of the Republic in Montevideo, Uruguay, received some support. It includes the clause that a planet also has to be "by far the largest body in its local population".Previously:
So Pluto would be out, because the 2300-kilometre-wide body is similar in size to many other objects in the same region, the chilly Kuiper Belt beyond Neptune. There would be only eight planets in the solar system, unless someone finds another really big one out there somewhere.
Some scientists had qualms about the sheer number of planets in the original scheme. Many of the icy objects in the Kuiper Belt are probably round, so we would soon end up with dozens of planets. Eventually there could be 200, according to Caltech astronomer Mike Brown, who has discovered several of these objects.
IAU planet definition Q&A sheet
And soon, there will be twelve planets