Sunday, June 17, 2007

The Dwarf Planet Eris: larger and more massive than Pluto

The Trans-Neptunian Object, and dwarf planet, Eris, charges once again. Mike Brown and Emily Schaller, published in Science the measurement of the joint mass of Eris and its moon Dysnomia through the orbital parameters of the latter (see links).

Both 10 meter Keck telescope (Mauna Kea, Hawaii) and Hubble Space Telescope (2.4 meters) were used for the determination of the orbit of Dysnomia.

The moon Dysnomia, orbits around Eris at a distance of 17430 km with a orbital period of 15.77 days. Eris and Dysnomia, together, possess a mass of 1.66x10^22 kg, which means: 27% more massive than Pluto. Given the 2400 km diameter of Eris, one concludes that it has a density of 2.3 g/cm^3. A value similar to those of the largest Trans-Neptunian Objects in contrast with the typical densities of the smallest (less that 1 g/cm^3).

These results seem to confirm that the smallest Trans-Neptunian Objects are more porous and less rich in rocky material that the largest.