IAU Classifies Pluto & Eris As "Plutoids"

Kligat writes "The International Astronomical Union has decided that Pluto and Eris should be classified as "plutoids," alongside their 2006 classification as dwarf planets. Under the definition, the self-gravity of a plutoid is enough for it to achieve a near-spherical shape, but not enough for it to clear its orbit of its rocky neighbors, and the plutoid orbits the Sun beyond Neptune." Reader FiReaNGeL links to a similar story at e! Science News.

Comments

Re:WTF is Eris?

[MRe_nl]

Eris, which measures about 70 miles wider than Pluto, is the farthest known object in the solar system at 9 billion miles away from sun. It is also the third brightest object located in the Kuiper belt, a disc of icy debris beyond the orbit of Neptune.

Calimero

[HetMes]

It's a stupid debate altogether. I image all the astronomers involved feel really good about themselves for making an impact. Why couldn't they leave well enough alone? Pluto will always be the ninth planet to me, despite Eris. Definitions be damned!

Re:Calimero

[Cochonou]

Classyfing Pluto as a Plutoid is not silly. Classifying Jupiter as a gas giant is not silly. Classying Mars as a telluric planet is not silly, either. This is exactly what you pointed out when you said that classifications were useful to catalog objects orbiting other stars.
Now, what I think people are objecting to is the apparent lack of logic for the "planet" classification itself. You get objects as different as gas giants and telluric planets under the same umbrella, "planet". So, why not Kuiper belt objects ?
But regardless of what has been the actual ruling about Pluto, the main problem lies in the redefinition process itself. What is a tomato, a fruit or a vegetable ? For biologists, it's a fruit, for cookers it's a vegetable. Everybody gets on with it. Different names for different fields, it's not uncommon. It has been going for ages.
Now, what went through the mind of the IAU to think that the "planet" word needed a formal science definition ? The ambiguity of this word had been acknowledged for ages, and there was some disagreement among astronomers. They could just as well have kept on using accurate names, such as gas giants or kuiper belts objects. It's as if some day, the "International Biologists Union" decided it was a good time to formally define the word "bug". And ruled that only insects should be called bugs, and not arachnids.
Anyway, it's not a big deal.

Re:WTF is Eris?

[spacemandave]

Eris, which measures about 70 miles wider than Pluto, is the farthest known object in the solar system at 9 billion miles away from sun. Eris is not the farthest known object in the solar system. It is a member of the "scattered disk," a subclass of Kuiper Belt objects (KBOs). It is the largest scattered disk object (SDO) discovered so far, but by no means the farthest away. This article has some nice diagrams that show the location of Eris relative to other known SDOs. There is another subclass of KBOs, called the "detached" objects, that are even further away. Sedna is a member of this family.

Re:WTF is Eris?

[spacemandave]

IIRC it is a kuiper belt object that actually isn't on the same plane as the other planets. I think I actually recall it being found by accident because it isn't where we would expected it to be, most likely it is a captured object not formed by our suns accretion disk. It is unlikely that any of the Kuiper Belt objects were captured from somewhere else. The Kuiper Belt is thought to have formed from the same accretion disk that formed the planets. However, it is thought that the original Kuiper Belt contained far more material than it does today, and that the objects were in more circular and coplanar orbits than we find them today. Due to an episode of giant planet migration, this original disk was scattered and depleted.

Many (but not all) of the observed dynamical features of the Kuiper Belt can be explained by giant planet migration.