My Very Excellent Mother Just Sent Us Nine Pies 'Xactly!

I will have to remember to ask Mel Evans to alter the memnonic for remembering the order of the planets to : - My Very Excellent Mother Just Sent Us Nine Pies 'Xactly!

More from the New Scientist on our tenth planet: -

The "tenth planet" is only slightly larger than Pluto, new Hubble Space Telescope images prove. It had been thought the planet, dubbed Xena, might be 25% to 30% larger.

Intriguingly, the downsizing means the distant world must be brighter than almost any other object in the solar system, suggesting it is constantly being resurfaced.

Xena, officially called 2003 UB313, was first announced in July 2005 and lies about three times as far from the Sun as Pluto. Its brightness suggested it was larger than Pluto, but it was not clear by how much because astronomers did not know how much sunlight its surface reflected.

Xena’s discoverers, led by Mike Brown at the California Institute of Technology in Pasadena, US, first thought its surface might be similar to that of Pluto, which reflects about 60% of sunlight. If so, Xena would be 25% larger than Pluto, an estimate borne out by recent ground-based observations of its heat, which suggested it was 30% larger.