It's looking more and more likely that we'll soon have to change those mnemonics for the planets. No more Matilda Visits Every Monday And Just Stays Until Noon Period. We'll have to add in Ceres, Charon and 2003 UB313...
Professor Owen Gingerich, who chairs the IAU planet definition committee, said: "In a sense we're demoting Pluto by taking it off the list of classical planets. But we're promoting it by making it the prototype of this new category of plutons."Ah, the politics of the IAU. Long may they debate.
The basis for this re-evaluation is a new scientific definition of a planet which uses gravity as the determining factor.
According to this definition, two conditions must be satisfied for an object to qualify as a planet:
* The object must be in orbit around a star, but must not itself be a star
* It must have enough mass for the body's own gravity to pull it into a nearly spherical shape
On whether he was confident the resolution would be passed, Professor Gingerich told the BBC News website: "It will be a very awkward situation if they don't.
"On Sunday afternoon, we proposed it out of the blue for the division chairmen and they voted unanimously that they would be prepared to back it. That's a good cross-section of astronomers.
"I'm sure it will be controversial to those with a stake in some other solution, but I hope we will get an overwhelming endorsement."