August 22, 2012
Dear Dr. Williams, Members of the IAU Executive Committee, Members of the
Secretariat, Members of the Working Group on Planetary System Nomenclature, Members of the Working Group on Small Bodies Nomenclature, and Delegates to the 28th IAU General Assembly,
For the second time, I am writing to respectfully request the General Assembly officially reopen the planet definition issue in order to address ongoing questions and controversy that resulted from the 2006 planet definition vote as well as to incorporate new data on objects in our own solar system and on exoplanets into a more broad, inclusive, and comprehensive understanding that streamlines the spectrum of sub-stellar bodies ranging from tiny asteroids and comets to the largest sub-brown dwarfs in this and in all stellar systems in the universe.
As I did in 2009, I ask specifically that you reconsider and add Resolution 5b from 2006, which would establish “planets” as a broad, umbrella category under which both classical and dwarf planets would be included; that the definition be expanded to include objects that orbit a star or are free-floating, to accommodate exoplanets and rogue planets; and that electronic voting be enabled to allow IAU members who are unable to physically attend General Assemblies to vote remotely.
In the six years since the 2006 vote, there have been significant discoveries in both our solar system and others that call into question the utility of the planet definition then adopted. Many exoplanets since discovered would not fit the planet definition adopted then even if it were expanded to include objects other than those that orbit the Sun. Astronomers have discovered exoplanet systems in which two planets share the same orbit; systems with two giant planets in 3:2 resonances; systems with as many as six planets all orbiting within a distance from their star comparable to Mercury’s orbit; planets that orbit their stars backward; and planets that formed directly from stellar nebulae the way stars do. Many exoplanets discovered have extremely elliptical, even comet-like, orbits.
In our solar system, the Dawn mission has revealed Vesta, which is not quite in hydrostatic equilibrium, to be far more like a terrestrial planet than like an asteroid. Vesta turns out to be a complex, geologically layered body with an iron core that formed in a process similar to the way terrestrial planets like Earth did. Dawn’s revelations have led some astronomers to question whether Vesta should be considered the solar system’s “smallest terrestrial planet. Vesta is not a simple ball of rock. This is a world with a rich geochemical history. It has quite a story to tell,” according to Dawn Principal Investigator Dr. Chris Russell.
As members of the IAU are well aware, Dawn is now departing Vesta and heading for Ceres, which it will study in similar detail.
The initial reason that prompted the 2006 General Assembly to determine a need for defining the term “planet” was the discovery of Eris, which was at the time believed to be larger than Pluto. However, in November 2010, when Eris occulted a star, a team of astronomers led by Dr. Bruno Sicardy determined that Eris is smaller than previously believed, marginally smaller than Pluto though about 27 percent more massive. This is significant because it calls into question the initial “need” for a definition since this “need” was based on erroneous information.
I am troubled by what appears to be an inflexible stand by the IAU, a determination to never reopen the planet definition discussion at any General Assembly, even into the indefinite future. This makes absolutely no sense. The 2006 discussion was based on new data discovered about Eris and the Kuiper Belt. Now, in 2012, we once again have more new data on bodies in this and other solar systems. Three years from now, we will have even more data on small planetary bodies via the Dawn mission to Ceres and the New Horizons mission to Pluto.
How can the IAU justify not reopening this discussion in light of all this new data? If this year’s General Assembly is determined to not take up the discussion, why not commit to putting it on the agenda for 2015? That would be an ideal time to take up the planet question again, as there will likely be a host of new information from the Dawn and New Horizons missions on two of the objects directly at the center of this debate.
As I did in 2009, I emphasize that this request is not about Pluto; it is about the need for a more useful, clear definition that encompasses both orbital dynamics and planetary geophysics, one that covers both our solar system and others.
The IAU considers communicating astronomy with the public as one of its essential tasks. I remind the organization that communication is a two-way street. Members of the public, astronomy enthusiasts, and amateur astronomers have consistently communicated dissatisfaction with the 2006 planet definition resolution. Isn’t it time the IAU hear them and respectfully respond to their concerns instead of ignoring and disenfranchising them?
Planetary science is constantly evolving with new discoveries, and in light of this, it makes sense that definitions will need to be updated and refined continuously. The 2006 vote was a first attempt at a definition, but it should not be considered a final one. This is not religion, where an authoritative body speaks once for all eternity, issuing a decree that can never be changed. By reopening the planet definition discussion, the IAU will affirm its relevance and flexibility through willingness to constantly reconsider previous decisions when new data call those decisions into question.
However, if the IAU continues to dig in its heals and refuse to even consider a new discussion on planet definition, the organization risks being viewed as emotional, bureaucratic, and dogmatic, and will become increasingly irrelevant as an authoritative body on the science of astronomy. At that point, other groups and individuals will very likely fill the void and take up the issue on their own, to the point that the matter may fall completely outside the influence of the IAU.
In order to further respectful two-way communication with the public, I urge the IAU to actively seek input on important issues such as this one from a broader population, including professional astronomers who are not IAU members, amateur astronomers and groups representing them, and astronomy students at all levels.
Regardless of the fact that no action on the planet classification issue has been planned for this General Assembly, I implore the IAU’s leadership, delegates to the GA, and members to do what needs to be done, to show courage and sensitivity to both scientists and lay people by admitting the planet definition issue remains unresolved and by adding a provision to this year’s GA reopening the planet definition discussion, or at least committing to putting it on the agenda of the 29th GA in 2015.
More specifically, I also ask that the Resolutions Committee place a resolution on the General Assembly floor for a vote on August 31, 2012, to officially reconsider resolution 5b of 2006, which if passed would establish dwarf planets as a subclass of planets. I also ask that a second resolution be put to the GA floor to include exoplanets in all further planet definition discussions. Finally, I ask that a resolution allowing for electronic voting be adopted before any other resolutions are considered to allow the IAU’s full membership to vote on all relevant issues, a provision badly needed in these difficult economic times when so many cannot afford the expense of travel and lodging to attend the GA in person.
Laurel E. Kornfeld
Highland Park, NJ, USA
Writer, amateur astronomer, astronomy student and blogger