Artists concept of the view from Eris with Dysnomia in the background, looking back towards the distant sun. Credit: A. Schaller (STScI)
From Wired Science coverage of CalTech release:
"[The] new results, obtained with Hubble Space Telescope and Keck Observatory data, indicate that the density of the material making up Eris is about two grams per cubic centimeter. This means that Eris very likely is made up of ice and rock, and thus is very similar in composition to Pluto. Past results from the Hubble Space Telescope had already allowed planetary scientists to determine that its diameter is 2,400 kilometers, also larger than Pluto's."
Eris (2003 UB313), a dwarf planet in the Kuiper Belt, has just been definitively measured -- however, it's bigger, and colder, than Pluto. This confirmation solidifies Pluto's status as a dwarf planet, and not one of the nine, or rather, eight, true planets in our solar system.
I once read (I will find out where) that the Kuiper Belt and Oort Cloud are so large that there could be multiple large ice planets out there, some the size of Mars and Earth.
Just more places for the colonization of the cosmos to mobilize.