Adding more fodder to the debate over the definition, when the New Horizons spacecraft flew by Pluto in 2015, it unveiled a world of surprising complexity, ranging from mountainous areas to vast nitrogen-ice lakes.
"We call Pluto a 'dwarf' planet, but it's just an adjective for 'planet,’” Runyon said. “It's still a planet, and that's where we take umbrage with the IAU.”
"Astronomers aren't experts in planetary science, and they basically passed a bunch of B.S. off on the public back in 2006 with a planet classification so flawed that it rules the Earth out as a planet, too," Stern remarked in 2016. "A week later, hundreds of planetary scientists, more people than at the IAU vote, signed a petition that rejects the new definition. If you go to planetary science meetings and hear technical talks on Pluto, you will hear experts calling it a planet every day."
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As a geomorphologist, Runyon is most particularly interested in the shape of landforms on worlds around the solar system. His dissertation deals with wind-blown sand geology on Mars, as mapped by the Mars Reconnaissance Orbiter's HiRISE (High Resolution Imaging Science Experiment) camera.
But he'll still keep his eye on the outer solar system. New Horizons is set to fly by a tiny world called 2014 MU69 on Jan. 1, 2019. While MU69 is too small to be even a dwarf planet, Runyon will be looking for features on MU69 such as ripples, which were also seen during the Rosetta mission during observations of Comet 67P/Churyumov–Gerasimenko. He'll also look at the shape of craters, among other things.
"MU69 has never warmed up since the formation of the solar system," he said. "It will be really interesting to see how different or complex it might be. There's a laundry list of things we'll be looking for, and hopefully we'll be surprised."
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