Plutoids, Dwarf Planets, and Centaurs?

It was just about a year ago that the International Astronomical Union demoted Pluto from planet to dwarf planet. At the same time, two other solar system objects -Eris and Ceres- were upgraded from lower categories. Ceres, discovered in 1801, is the largest asteroid belt object, and is composed of a rocky mantle and icy crust. It may also have a liquid ocean and water vapor in its atmosphere, making it a prime candidate in the search for life on other planets. Eris resides three times farther from the sun than Pluto, in the ’scattered disk’ beyond the Kuiper Belt, and is larger than both Ceres and the former planet. It too has a moon, named Dysnomia (the pair’s names come from the Greek goddess Eris (of discord) and her daughter (of lawlessness). The pair are currently the farthest known objects in the solar system. But back to Pluto. Poor Pluto, no longer an equal of mighty Jupiter and fair Venus, relegated with the rest of the tiny rocks of the solar system…. until now! As of June 11th, Pluto and Eris are reclassified as ‘Plutoids’ – as they are both dwarf planets and Trans-Neptunian Objects (Ceres does not qualify). What difference does this make? None. It seems like a poor consolation prize to me, and kitschy to boot. If it was meant to rectify the disgace conferred upon our ninth planet (or whatever it is now) with a whole category, the fact that there are only two members is rather sad… In other interesting solar system information, there are droves of icy planetoids wandering between the orbits of Jupiter and Neptune, called Centaurs (orange above). These lie inward of the Kuiper Belt (green) but outside the asteroid belt (pink). Nifty.

For more information on dwarf planets, click here.