Scientists once again in the 'great planetary debate'

Washington, September 22 : Scientists have again started the great debate on the exact definition of a planet, and have come out with conflicting viewpoints.

Two years ago, the International Astronomical Union (IAU) elected to define the term planet, restricting it to the eight largest bodies orbiting the Sun, and deleting Pluto from the list.

The demotion of Pluto sparked considerable public controversy.

Numerous planetary scientists and astronomers protested the IAU's definition as not useful, while numerous other planetary scientists and astronomers supported the outcome.

Recognizing the need for further scientific debate on planet definition, more than 100 scientists and educators representing a wide range of viewpoints on the issue converged for three days on the Applied Physics Laboratory of Johns Hopkins University (APL) for "The Great Planet Debate: Science as Process" conference last month.

NASA, APL, the Planetary Science Institute, The Planetary Society, and the American Astronautical Society sponsored the conference.

Different positions were advocated, ranging from reworking the IAU definition (but yielding the same outcome of eight planets), replacing it with a geophysical-based definition (that would increase the number of planets well beyond eight), and rescinding the definition for planet altogether and focusing on defining subcategories for serving different purposes.

No consensus was reached.

According to planetary scientist Alan Stern, "I was impressed with two things that came out of The Great Planet Debate meeting: first, that no one liked the IAU's definition of planethood, and second, that there are strongly divergent scientific opinions about what a planet is, with those who study orbits and those who study planets themselves seeing the matter very differently."

"My view is that the dynamically based definitions are deeply flawed because they do not take into account any physical properties of the body in question, and give ridiculous results, for example classifying identical large objects in different orbits differently-so that even Earths are not always planets, which is crazy," Stern concluded.

"The word 'planet' has a deep cultural context that cannot be decided by vote of a subset of astronomers meeting in a room somewhere, especially when that debate is rushed and the vote close," said William McKinnon, a Professor of Earth and Planetary Sciences at Washington University in St. Louis, and an IAU member.

"The IAU should reopen the issue to electronic debate by the entire astronomical community. I am sure the outcome in that case, whatever it turns out to be, or even if it is concluded that no universal definition is necessary, would be more satisfactory to all parties," he added.

ANI