Pluto now a plutoid

The new official name. [Link]

The name plutoid was proposed by the members of the IAU Committee on Small Body Nomenclature (CSBN), accepted by the Board of Division III and by the IAU Working Group for Planetary System Nomenclature (WGPSN), and approved by the IAU Executive Committee at its recent meeting in Oslo, according to a statement released today.

Here's the official new definition:

"Plutoids are celestial bodies in orbit around the sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit."

In short: small round things beyond Neptune that orbit the sun and have lots of rocky neighbors.

The two known and named plutoids are Pluto and Eris, the IAU stated. The organization expects more plutoids will be found.

"Rather than resistance to 'plutoid,' I think we'll just be hearing groans," said Stephen J. Kortenkamp, senior scientist at the Planetary Science Institute in Tucson.

There is controversy.

The term plutoid joins a host of other odd words -- plutinos, centaurs, cubewanos and EKOs -- that astronomers have conjured in recent years to define objects in the outer solar system, whose appearance seems to grow more complex every year.

Kortenkamp wonders if "plutoid" isn't just one more confusing term in the cosmic lexicon.

"So Pluto is a Kuiper belt object, a plutino (the unofficial but nearly universally accepted name for objects in the 2:3 resonance with Neptune), a dwarf planet, and now also a plutoid?" he said. "If the IAU is trying to make things more clear, I think it needs to try again. This is just another layer of confusion that will feed the "pluto is a planet" camp at the [Johns Hopkings] meeting."

Kortenkamp also thinks the new defiinition leaves Ceres up in the air: "And this "-oid" classification doesn't apply to Ceres?" he asks. "Okay, so does that means we continue calling Ceres an ASTERoid?"

Asked if Ceres remains a dwarf planet and is not an asteroid, Bowell, the IAU official, said: "I think so!"