http://www.astroarts.com/news/2008/06/13plutoid/index-j.shtml
国際天文学連合、冥王星型天体の英語名をplutoidに決定
2006年夏の国際天文学連合（IAU）総会で、太陽系の惑星の定義が採択されました。実は、そのときに同時に、「太陽系外縁天体（注1）で、なおかつ準惑星」という新しい天体の分類を作ることも採択されました。しかし、この分類を新しく作ること自体は採択されたのですが、残念ながら、英語名については合意には至りませんでした。
その後、日本国内では、日本学術会議 物理学委員会IAU分科会の中に、「太陽系天体の名称等に関する検討小委員会」（委員長：海部宣男（かいふのりお）IAU日本代表、前国立天文台長）が設置され、太陽系天体の英語名に対応する推奨和名を決定しました。
dwarf planetには準惑星、trans-Neptunian objectには太陽系外縁天体という和名が付けられました。上記の新しい分類の天体については英語名すらIAUで決まっていませんでしたが、委員会では様々な観点からの議論を総合して、冥王星という長い間親しまれた天体に敬意を表する意味合いを込めて、「冥王星型天体」という和名を推奨することにし、IAUにもその趣旨にそった名前を決めてほしいという要望を提出しました。
この要望を受けて、IAUで太陽系天体を扱う第三部会の中でも議論がすすみ、このたびノルウェーのオスロで開催されたIAU評議員会で、最終的にplutoidという英語名にすることが決定されました。冥王星の英語名であるPlutoをもとにした、冥王星の仲間という意味での命名です。冥王星という名前を大事にする「冥王星型天体」という推奨和名とも相性のよい命名となりました。
太陽系天体の名称等に関する検討小委員会の委員でもあり、今回のIAU評議員会に出席した岡村定矩（おかむらさだのり）・東京大学副学長は、「冥王星という天体に敬意を表するという方向性で決まった日本の推奨和名と、ほぼ同じニュアンスを持つ英語名に決まったことは、たいへんよかったと思っています」と述べています。
現在、冥王星型天体に分類されているのは冥王星とエリスだけですが、今後は増えていくと考えられます。第三部会の中では、今後、太陽系外縁天体の中でも絶対等級（注2）が1等よりも明るいものについて、冥王星型天体の候補として固有の名前をつけることになっています。冥王星は、いわば太陽系を構成する新しい種族、「冥王星型天体」の盟主として復権したといえるでしょう。
注1：海王星よりも外側に存在する（軌道長半径が海王星の軌道長半径よりも大きな）天体。
注2：太陽系内の天体の場合、太陽および地球から天体までの距離を1天文単位（地球と太陽との間の平均距離）とし、位相角（天体から見た太陽と地球の間の角度））を0°としたときに、地球から見たその天体の見かけの明るさを絶対等級という。
http://www.sciencenews.org/view/generic/id/33158/title/From_planet_to_plutoid_
From planet to plutoid
Pluto and its kind get new name
TITLE-PERFECT PLUTOIDSThe dwarf planet, Pluto, and its counterpart Eris are the first two members of a new class of objects called plutoids. Both lie beyond Neptune and are large enough that gravity pulls them into spherical forms. Any newfound object with similar traits will also fall into this IAU-established, dwarf-planet category.IAU, NASA/ESA Hubble Space Telescope, H. Weaver (JHU/APL), A. Stern (SwRI), the HST Pluto Companion Search Team and M. Brown.
Pluto now has a family of its own, after astronomers have struggled for years to give it a place among its celestial brethren. The International Astronomical Union announced June 11 that it has accepted the name plutoid to distinguish all dwarf planets lying beyond Neptune. Last summer, the members of the IAU Committee on Small Body Nomenclature, or CSBN, proposed classifying these objects under the new title, which the IAU Executive Committee approved at its recent May meeting held in Oslo, Norway. “We wanted a rather clear name that related to Pluto,” says astronomer Brian G. Marsden, secretary of the CSBN. “Plutoid fit the bill. And I am happy enough with it. It means Pluto-like.” A plutoid is defined as a type of dwarf planet that orbits the Sun at a distance greater than Neptune and has enough mass for its self-gravity to give it a near-spherical shape. This characterization means “we have two known and named plutoids: Pluto and Eris,” says Marsden of the Harvard-Smithsonian Astrophysical Observatory. But there are more plutoids to find and more known ones to name, he adds. “We just needed the protocol to name the objects, and that is what this news does.” Two years ago, the IAU voted to kick Pluto out of the planet family and demote it to what they called a dwarf planet. But, Marsden says, Ceres, which is in the asteroid belt between Mars and Jupiter, also fit that bill, so scientists needed to distinguish between rocky dwarf planets like Ceres and icy ones like Pluto. At the IAU meeting in Prague where Pluto was demoted, CSBN committee members tried to agree on labels to distinguish dwarf planets as either Pluto-like or Ceres-like. “We came up with plutonian, but the name did not pass.” Although that vote was close, plutonian ended up two or three votes shy of acceptance, the astronomer says. “I have to admit I didn’t vote for it,” he says. “The reason is because I felt that if they wanted plutonian, then we needed a label for Ceres-like objects. It just does not make sense to call Ceres a plutonian. That is why I voted against the name for Pluto-like dwarves back then.” Marsden says that IAU president Catherine Cesarsky had been hoping that the committee would come up with a title for the minor planets like Pluto for past two years. “Cesarsky must be very happy with plutoid. It is all over the IAU’s press release and even in italics,” he says. Ceres is not a plutoid because it does not lie beyond Neptune. But Marsden noted that the committee recommended to the IAU Executive Committee to name Ceres-like objects ceroids. The IAU did not accept that name because current scientific knowledge leads astronomers to believe that Ceres is the only object of its kind. “That is news to me,” Marsden says. “But maybe if we do find some bigger stuff similar to Ceres, ceroid could be accepted too.” At any rate, the astronomer says, now that the IAU has accepted plutoids, the CSBN, which is responsible for naming minor planets and asteroids, can start working with the IAU’s Working Group for Planetary System Nomenclature, or WGPSN, to determine the names of new plutoids. Previously, the two committees worked together to name the dwarf planet — and now plutoid — Eris and its satellite Dysnomia. The relationship between the committees is important because it helps ensure that objects in different categories aren’t given the same name as any other small body in the solar system, the Marsden says. “And keep watching,” he adds, “because now that we’ve gotten the go-ahead from the IAU, the third plutoid will be named soon.” The astronomer did not say what the name of the next plutoid would be. “Announcing that wouldn’t be fair because it is not official,” he says. “But I’ll tell you, the one we are working on now is 2005FY9 and the name was proposed by its discoverer, Mike Brown. We, the CSBN, like the name and the WGPSN is considering it right now. So we should know in a few weeks.” Up next for naming, is plutoid 2003EL61, Marsden adds.
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