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Hail Eris, king of the dwarf planets

Eris, named after the goddess of strife and discord, just won't leave Pluto alone. Its discovery (at the time, it went by the less appealing name 2003 UB313) prompted a reevaluation of what it meant to be a planet. That ultimately resulted in Pluto having its planetary status revoked. Pluto became the founding member of the new class called dwarf planets, and 2003 UB313 took the official name of Eris and joined it in that club. 老域名购买

Planetary demotion seems to just have been the first step in what appears to be an ongoing campaign by Eris to diminish the significance of Pluto. Research published in 2006 revealed that Eris was larger than Pluto; now, observations that will appear in today's Science indicates that it's heavier, too.

The work relied on another discovery from 2006: Eris has a moon, Dysnomia (named after Eris's daughter and meaning lawlessness). Observations from the Hubble and the ground-based Keck telescope at various dates in 2006 allowed Dysnomia's orbit to be reconstructed. From there, Kepler and a bit of math produced an orbit in good agreement with the observations. The orbit that resulted, combined with the fact that Dysnomia and Eris appear to be formed from similar material, suggest that the moon formed from debris blasted out of Eris by a collision.

Kepler's laws also allowed the calculation of the total mass of the system, placing it at 1.66 x 1022kg. Since Dysnomia's mass appears negligible compared to that of Eris, we can assign that weight to Eris, which makes it the most massive dwarf planet, 25 percent heavier than Pluto.

The two dwarves appear to have similar densities, consistent with them being primarily made from rocky material. This suggests that whatever we learn from the New Horizons probe when it makes it to Pluto will likely apply to Eris. All we have to do is wait until 2015 for it to get there.


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