Last night during a talk I gave about the night sky, a woman asked why Pluto is not a planet. She, like many other people who’ve attended my classes and talks since August 24, 2006, the day the erstwhile planet was demoted to dwarf planet, was still attached to the idea that it should remain a planet. Her reasons were based partly on sentiment and partly on the new data from the New Horizons 2015 flyby that revealed a world so active, it resembled a planet in every other way but semantically.
We went over the new definition, its origin and how a select group of astronomers voted to demote Pluto. And I do mean select — some astronomers don’t accept the change. But I also explained that since the early 1990s, astronomers have been discovering lots of objects orbiting near and beyond Pluto that resemble that 1,477-mile-wide globe in size, composition and orbit. Unless we want to start calling them all planets, it makes a lot of sense to view the whole lot as icy asteroids that occupy the far reaches of space beyond Neptune. They’re the reason for the push to redefine Pluto.
Well, I’m here to report that lovers of Pluto as a planet have another small reason to celebrate. Pluto has dunes! In the June 1 issue of Science, Matt Telfer (University of Plymouth, UK) and his team believe they have identified dunes in Sputnik Planitia on Pluto, a bright, craterless region of nitrogen, carbon monoxide and methane ice that forms part of the dwarf planet’s “heart.”
Their models reveal that dunes could form when sand-sized grains of methane ice are blown about by prevailing winds in Pluto’s atmosphere. They write that the methane grains “could have been lofted into the atmosphere by the melting of surrounding nitrogen ice or blown down from nearby mountains” with speeds topping out around 20 mph (10 meters/sec) to create regularly spaced, linear ridges resembling transverse dunes seen on Earth.
Learn how Pluto’s dunes form
Heat from the sun vaporizes nitrogen and methane ice in the mountains, releasing a blizzard of methane crystals. Blown by the wind they eventually fall under the force of gravity, strike the ground below and release more grains that are gathered into dunes by the dwarf planet’s bitter cold breezes.
Once again, a process familiar on Earth finds its analog on a lively little ball of ice 3.7 billion miles from the sun. Will Pluto fight its way back to planethood one day? Maybe not, but it continues to blur the distinction we make between asteroid and planet.