Pluto Barrackers Take Another Hit (June 15, 2007)

    In August 2006 the International Astronomical Union reclassified Pluto as a dwarf planet, following the discovery of what was finally dubbed Eris, an object in the Kuiper belt, as is Pluto. The reason for the IAU reclassification from planet to dwarf planet was the observation that Eris was in fact significantly larger (in volume) than Pluto.

What was still in doubt was the relative masses of the two bodies.

No longer, Michael E. Brown and Emily L. Schaller of the Division of Geological and Planetary Sciences, California Institute of Technology, report in today's issue of Science that Eris has a mass of 1.67 x 10²² ± 0.02 x 10²² kilograms, or 1.27 ± 0.02 that of Pluto.

The authors conclude, "From this mass measurement and the previous size measurements [2400 ± 100 km], we can calculate the density of Eris. This density is consistent with the moderately high 2.03 ± 0.06 for Pluto.

However, the IAU designation for both Pluto and Eris remains: dwarf planets.