APOD: 2007 June 19 - Eris: More Massive than Pluto Explanation: Eris, a dwarf planet currently orbiting the Sun at about twice Pluto's distance, has been measured to have about 27 percent more mass than Pluto. The mass was calculated by timing the orbit of Eris' moon Dysnomia. Images taken with a ground-based Keck telescope, when combined with existing images taken by Hubble Space Telescope, show that Dysnomia has a nearly circular orbit lasting about 16 days. Cataloged as 2003 UB313 only a year ago, infrared images also showed previously that Eris is actually larger in diameter than Pluto. The plane of Eris' orbit is well out of the plane of the Solar System's planets. In the above drawing, a scientific artist has imagined Eris and Dysnomia orbiting our distant Sun. No space missions are currently planned to Eris, although the robotic New Horizons spacecraft bound for Pluto has recently passed Jupiter.
APOD: 2008 July 16 - Makemake of the Outer Solar System Explanation: Recently discovered Makemake is one of the largest objects known in the outer Solar System. Pronounced MAH-kay MAH-kay, this Kuiper belt object is only slightly smaller than Pluto, orbits the Sun only slightly further out than Pluto, and appears only slightly dimmer than Pluto. Makemake, however, has an orbit much more tilted to the ecliptic plane of the planets than Pluto. Designated 2005 FY9 soon after its discovery by a team led by Mike Brown (Caltech) in 2005, the outer Solar System orb was recently renamed Makemake for the creator of humanity in the Rapa Nui mythology of Easter Island. Additionally, Makemake has been recently classified as a dwarf planet under the new subcategory plutoid, making Makemake the third cataloged plutoid after Pluto and Eris. Makemake is known to be a world somewhat red in appearance, with spectra indicating it is likely covered with frozen methane. Since no images of Makemake's surface yet exist, an artist's illustration originally meant to depict Sedna has been boldly co-opted above to now illustrate Makemake. A hypothetical moon is visualized above nearly in the direction of our distant Sun.
APOD: 2008 September 23 - Haumea of the Outer Solar System Explanation: One of the strangest objects in the outer Solar System was classified as a dwarf planet last week and given the name Haumea. This designation makes Haumea the fifth designated dwarf planet after Pluto, Ceres, Eris, and Makemake. Haumea's smooth but oblong shape make it extremely unusual. Along one direction, Haumea is significantly longer than Pluto, while in another direction Haumea has an extent very similar to Pluto, while in the third direction is much smaller. Haumea's orbit sometimes brings it closer to the Sun than Pluto, but usually Haumea is further away. Illustrated above, an artist visualizes Haumea as a nearly featureless ellipsoid. Quite possibly, however, Haumea has interesting craters and surface features that currently remain unknown. Originally discovered in 2003 and given the temporary designation of 2003 EL61, Haumea was recently renamed by the IAU for a Hawaiian goddess. Haumea has two small moons discovered in 2005, recently renamed Hi'iaka and Namaka for daughters of the goddess.