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IAU Press Release 01/99

February 3, 1999:


Recent news reports have given much attention to what was believed to be an initiative by the International Astronomical Union (IAU) to change the status of Pluto as the ninth planet in the solar system. Unfortunately, some of these reports have been based on incomplete or misleading information regarding the subject of the discussion and the decision making procedures of the Union.

The IAU regrets that inaccurate reports appear to have caused widespread public concern, and issues the following corrections and clarifications:

  1. No proposal to change the status of Pluto as the ninth planet in the solar system has been made by any Division, Commission or Working Group of the IAU responsible for solar system science. Accordingly, no such initiative has been considered by the Officers or Executive Committee, who set the policy of the IAU itself.

  2. Lately, a substantial number of smaller objects have been discovered in the outer solar system, beyond Neptune, with orbits and possibly other properties similar to those of Pluto. It has been proposed to assign Pluto a number in a technical catalogue or list of such Trans-Neptunian Objects (TNOs) so that observations and computations concerning these objects can be conveniently collated. This process was explicitly designed to not change Pluto's status as a planet.

    A Working Group under the IAU Division of Planetary Systems Sciences is conducting a technical debate on a possible numbering system for TNOs. Ways to classify planets by physical characteristics are also under consideration. These discussions are continuing and will take some time. The Small Bodies Names Committee of the Division has, however, decided against assigning any Minor Planet number to Pluto.

  3. From time to time, the IAU takes decisions and makes recommendations on issues concerning astronomical matters affecting other sciences or the public. Such decisions and recommendations are not enforceable by national or international law, but are accepted because they are rational and effective when applied in practice. It is therefore the policy of the IAU that its recommendations should rest on well-established scientific facts and be backed by a broad consensus in the community concerned. A decision on the status of Pluto that did not conform to this policy would have been ineffective and therefore meaningless. Suggestions that this was about to happen are based on incomplete understanding of the above.

The mission of the IAU is to promote scientific progress in astronomy. An important part of this mission is to provide a forum for debate of scientific issues with an international dimension. This should not be interpreted to imply that the outcome of such discussions may become official IAU policy without due verification that the above criteria are met: The policy and decisions of the IAU are formulated by its responsible bodies after full deliberation in the international scientific community.

          Johannes Andersen           General Secretary, IAU

For more information, contact the Secretariat or the Division President, Prof. M.F. A'Hearn, Univ. of Maryland, USA.


The International Astronomical Union (IAU), founded in 1919, is the international non-governmental organization uniting professional astronomers all over the world. It currently has 61 Member States and over 8,300 Individual Members in 83 countries. Its scientific activities are coordinated by 11 Divisions and 40 Commissions spanning the entire field of astronomy. The IAU is integrated in the international scientific community through its membership of the International Council for Science (ICSU) and represents astronomy in committees of the UN and other international organizations. The permanent IAU Secretariat is located in Paris, France. (see below).


IAU/UAI Secretariat
Institut d'Astrophysique Tel: +33 1 4325 8358
98bis, Bld. Arago Fax: +33 1 4325 2616
F - 75014 Paris E-Mail:     iau@iap.fr
France WWW:     http://www.iau.org


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