Interview with the IAU President on Pluto's Demotion

Last month, Catherine Cesarsky became the president of the International Astronomical Union (IAU).  Cesarsky, the first woman to hold this prestigious position, started her presidency at a time when many scientists are questioning IAU's recent decision to strip Pluto of its planetary status based on a vote of just 424 members at a meeting in Prague.

Cesarsky served as the director general of the European Southern Observatory since 1999 and is famed for her research work in central areas of modern astrophysics. She also led the design and construction of the ISOCAM camera onboard the Infrared Space Observatory (ISO) of the European Space Agency (ESA).

In an email interview with, Cesarsky discusses her thoughts on the role of the IAU as a governing body and the split of the scientific community on the new definition and the way the process was handled, effectively excluding 10,000 professional astronomers around the globe. How does the IAU expect to handle the Pluto flap? Many people, including a lot of astronomers, are not happy with this decision.

Catherine Cesarsky: As you probably know, the scientific progress of planetary astronomy over the past decade-especially the discovery of one object larger than Pluto (2003 UB313)-made it necessary to define the term "planet". The IAU had to make a decision on this topic to start the naming process for 2003 UB313.

We knew in advance that no matter how this decision would come out, a part of the astronomical community would be disagreeing. The intense debate at the 2006 General Assembly was very healthy and exactly intended to make as large a fraction of the community as possible, agree with the decision. In this we succeeded.

It also has to be said that the - now very visible - "splitting" of the community in the issue of where to make the delineation between planets and other solar system objects is not new. It is a debate that has existed for several years. Has the intense debate strengthened or weakened the authority of the IAU? What does the group need to do to keep its position as a governing body?

CC: It is too early to tell. The IAU has a rigorous set of Statutes, Bylaws and Working Rules. These have been followed carefully in this process of developing the planet definition Resolution and in the voting process.

A controversial subject such as this merits debate as we had during throughout the General Assembly. The astronomers present could ponder on the arguments expressed and prepare for voting. Our Statutes state that Resolutions can only be passed by a majority of those IAU members present and voting. Resolution 5A was passed with a wide majority. There is therefore, from our perspective, little reason to question the authority of the IAU. How, if, or when will the IAU try to define extrasolar planets, stars, and planemos? Will there be a new definition for them as well?

CC: The IAU indeed intends to work on these interesting questions over the next three years. For instance the delineation between brown dwarfs and planets remains to be defined. This issue was already discussed at the first meeting of the new EC together with the new Division Presidents on the last day of the General Assembly. Should there be some outreach dedicated to educating the public on such decisions and what they mean?

CC: The IAU has recently reinforced its public communication. A Resolution was for instance passed on this topic during the General Assembly.

An excerpt says: "Sharing what we learn about the universe is an investment in our fellow citizens, our institutions, and our future. Individuals and organizations that conduct astronomical research-especially those receiving public funding for this research-have a responsibility to communicate their results and efforts with the public for the benefit of all."

One example of IAU's implementation of these words could be seen in the completely open information flow that took place during the 2006 General Assembly. Another example is that the Executive Committee decided during the GA to announce that the IAU is willing to coordinate and play a leading role in the 2009 International Year of Astronomy as a catalyst and a global coordinator.

Full Coverage: The Debate and the IAU Vote

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Sara Goudarzi
Sara Goudarzi is a Brooklyn writer and poet and covers all that piques her curiosity, from cosmology to climate change to the intersection of art and science. Sara holds an M.A. from New York University, Arthur L. Carter Journalism Institute, and an M.S. from Rutgers University. She teaches writing at NYU and is at work on a first novel in which literature is garnished with science.