Indeed, there are likely to be more intermediate solar system objects that are in the fuzzy 'roundish' area than there are objects that are clearly round. But the proposed 'geophysical' definition of planethood based upon roundness uses a poor criterion because there is no good dividing line. 'Gravity forces large bodies to be round, whereas small bodies can be quite oddly shaped. '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. '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.' said planetary scientist Alan Stern, currently a visiting scholar at the Lunar and Planetary Institute of Houston, Texas. No consensus was reached.Ī sample of the opinions expressed by conference participants follows: The conference was sponsored by NASA, APL, the Planetary Science Institute, The Planetary Society, and the American Astronautical Society.ĭifferent 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. 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. Numerous planetary scientists and astronomers protested the IAU's definition as not useful, while numerous other planetary scientists and astronomers supported the outcome. The demotion of Pluto sparked considerable public controversy.

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.

Psi definition