Gingerich argued that “a planet is a culturally defined word that changes over time,” and that Pluto is a planet. Williams defended the IAU definition, which declares that Pluto is not a planet.
If the planet is larger then Pluto (for example something as big as Mars) and can support a large atmosphere, terraforming will be somehow possible. First of all, by warming the planet, its gasses will evaporate and will create a giant atmosphere. Then, as temperature rises, water ice will also melt.