Pluto used to be a full-fledged planet, and then in 2006 it wasn't. But the debate over its status continues, and you can watch one discussion live tonight.

The International Astronomical Union's 2006 decision to demote Pluto to a "dwarf planet" takes center stage in a debate at 8 p.m. EDT (0000 April 30 GMT) by the Philosophical Society of Washington in Washington, D.C. You can watch live here , in the window above, or directly from the PSW Science group here.

Alan Stern, the principal investigator of the New Horizons mission that flew past Pluto in 2015, has been a fierce advocate of Pluto remaining a planet . He will battle it out with Ron Ekers, a past president of the International Astronomical Union (IAU) who led the organisation from 2003 to 2006, when Pluto's demotion occurred. The IAU is the international body that governs the naming of celestial objects.

Stern will discuss what he sees as scientific issues surrounding the definition for the term "planet," and he will propose a newer definition that is more inclusive of small bodies such as Pluto. Ekers will argue in favor of the IAU definition, which has a distinct taxonomy for little worlds that are far out in the solar system in a region known as the Kuiper Belt.

The push to give planethood back to Pluto accelerated after the New Horizons flyby of the object, which revealed that Pluto had mountains, vast seas and other complex features. Stern argues that its geology is more reminiscent of a planet's than a smaller world's geology.