Pluto gets recognition it deserves, well, sorta

William Atkins
Thursday, 12 June 2008 21:32

Science - Space

So far only Eris, besides Pluto, has been named within the plutoid classification. Eris is larger than Pluto and further away from the Sun that Pluto.

Specifically, Eris orbits the Sun three times farther out than Pluto. Also, it is estimated to be 1,500 miles (2,500 kilometers) in diameter, and 27% more massive than Pluto. Its diameter makes it the ninth largest object known to be orbiting the Sun.

To be classified as a “plutoid” an object must circle the Sun; be smaller than the minimum size for a planet; be not too large so that gravity gives them a near-spherical shape; and be further from the Sun than the planet Neptune.

Specifically, the IAU states, “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 neighbourhood around their orbit. Satellites of plutoids are not plutoids themselves, even if they are massive enough that their shape is dictated by self-gravity. The two known and named plutoids are Pluto and Eris. It is expected that more plutoids will be named as science progresses and new discoveries are made.” [IAU press release]

Here are some comments from astronomers after hearing about the news:

“Plutoids or hemorrhoids, whatever they call it. This is irrelevant.” –Dr. Alan Stern, former NASA space sciences chief. [Time]

‘Instead of being a "puny" outer planet, Pluto is now a "prototype of a new type of fascinating objects.’” --Catherine Cesarsky, IAU president [Los Angeles Daily News]

"It [plutoid] doesn't really roll off the tongue very well. Maybe it'll make it." --Mike Brown, the California Institute of Technology astronomer who discovered Eris in 2003. [Times Record News}

"It's going in the right direction. I'd still rather have it just be known as a planet." and "I grew up with nine planets, I'm sorry," Ralph McNutt, a planetary scientist at Johns Hopkins University. [AZCentral]
“We wanted a rather clear name that related to Pluto. “Plutoid fit the bill. And I am happy enough with it. It means Pluto-like.” --Astronomer Brian G. Marsden, secretary of the CSBN (IAU). [Science News (subscription required)]

"The IAU is a democratic organization, thus open to comments and criticism of any kind. Given the history of the issue [Pluto], we will probably never reach a complete consensus." --Karel A. van der Hucht, IAU General Secretary [PhysForum.org]