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Using the images and data so far received from New Horizons, planetary scientists outline some of their tentative conclusions as well as speculate about what it means.
[Alan Stern, New Horizons’ principal investigator] says Pluto’s surface appears to be much less heavily cratered than its large moon, Charon—which implies that the surface has been paved over in some way. That smoothing process could come from internal heat that keeps rock and ice soft, or by the frosts that snow down and blanket the surface in fresh ice. “Either [Pluto’s] internal engine continues to run, and there are active processes that are taking place,” Stern says, “or those atmospheric processes are themselves covering up the geology, and covering up the craters.”
Jonathan Lunine, a planetary scientist at Cornell University, not on the New Horizons team, favors the latter explanation. His initial impression is that Pluto is far more cratered than Triton, the moon of Neptune that is about the same size as Pluto and is thought to be a captured Kuiper belt object. Triton has a famous “cantaloupe” terrain, thought to have formed as heat, driven by Saturn’s tidal pull, allowed molten blobs of ice to rise and overturn. Parts of Pluto’s rugged surface seem to be far more carved and cratered, Lunine says. “It’s telling me that [Pluto’s] crust was not heated and modified to the extent that it was on Triton.”
Above all, however, I like Lunine’s comment at the end of the article:
Lunine says the emerging diversity on Pluto—of both active atmospheric and geological processes—makes him disagree with the decision of International Astronomical Union to call Pluto a dwarf. “This really is a planet,” he says. He notes that electrons have a double definition as a particle and a wave. “Why can’t we call Pluto a planet and a Kuiper belt object?” he asks. “I think we have to think of it as both.”