Is the moon a planet? How about Pluto? Astronomical authorities say no, but Alan Stern, who led the research on the New Horizons probe to Pluto, begs to differ. Stern is part of the team behind a new paper published in Planetary and Lunar Sciences, which argues that the existing definition of "planet" is flawed. Under Stern's new definition, the moon, Pluto and more than 100 other solar system objects would be upgraded to planets. At present, a planet is defined by the International Astronomical Union (IAU) as an object that orbits a star, is rounded by its own gravity, is not massive enough to create thermonuclear fusion (which excludes stars that orbit other stars) and has cleared its orbit of planetesimals. Stern points out several flaws in the IAU definition: it doesn't include "rogue planets" with no star to orbit, it requires planets to "clear their neighborhoods," which is impossible to do entirely since small objects are constantly entering and exiting planetary orbits, and it