Mabfan's Musings

Pluto IS still a planet in a lot more than just people's hearts. Only four percent of the IAU voted on the controversial demotion, and most are not planetary scientists. Hundreds of professional astronomers led by New Horizons Principal Investigator Dr. Alan Stern signed a formal petition rejecting the IAU definition and the demotion. The New Horizons mission continues to refer to Pluto as a planet. This is an ongoing debate with two equally legitimate views. Brown's is the dynamical planet definition. The alternative is a geophysical planet definition, in which a planet is any non-self luminous spheroidal body orbiting a star. In other words, if the object is large enough to be rounded by its own gravity, a state known as hydrostatic equilibrium, and it orbits a star, it's a planet. By this definition, Ceres is a planet, as are Pluto, Haumea, Makemake, Eris, and any other dwarf planet large enough to be spherical. Dwarf planets are simply a third class of planets in addition to terrestrials and jovians--objects orbiting a star and large enough to be spherical but not large enough to gravitationally dominate their orbits.