Purdue team finds convection could produce Pluto’s polygons

On Pluto, icebergs floating in a sea of nitrogen ice are key to a possible explanation of the quilted appearance of the Sputnik Planum region of the dwarf planet’s surface. Data reported by NASA’s New Horizons New Horizons mission to the Pluto system shows unusual terrain in this region, which features a large deposit of nitrogen ice with a pattern of polygons that are thickest at their centers and dip at their edges. Purdue University researchers have proposed that the polygons seen in the images could be individual Rayleigh-Bénard convection cells. A paper detailing the work will be published in the journal Nature online on Thursday (June 2).


“Evidence suggests this could be a roiling sea of volatile nitrogen ice,” Melosh said. “Imagine oatmeal boiling on the stove; it doesn’t produce one bubble for the entire pot as the heated oatmeal rises to the surface and the cooler oatmeal is pushed down into the depths, this happens in small sections across the pot, creating a quilted pattern on the surface similar to what we see on Pluto. Of course, on Pluto this is not a fast process; the overturn within each unit happens at a rate of maybe 2 centimeters per year.”


“Within this pool of nitrogen ice, there are mountains of water ice that have collected at the edges of the polygons,” he said. “The way they have collected suggests they have moved or floated like icebergs with the convection current. If this is true, we can calculate how deep the pool would need to be for the icebergs to float freely without catching on the bottom.”





Overturn from convection would erase impact craters and renew this section of the dwarf planet’s surface, which fits with the data New Horizons provided. From this data the surface of Pluto’s Sputnik Planum is estimated to be less than 10 million years old, which is considered very young and suggests significant activity on the surface. However, the Purdue team’s convection model suggests that the age of the surface of the nitrogen ice fields of the Sputnik Planum region is even younger, around one million years old, he said.





“Pluto has surprised us, but you never know what you will see until you get there,” said Steckloff, who performed analysis of the annual thermal changes on Pluto and evaluated alternative explanations for the polygon terrain. “This underscores the importance of these missions, which provide rich data, but also reveal new questions and how much we don’t know. We look forward to the complete analysis of the surface composition and how it affects our model. However, definitive confirmation of our model would require another mission to probe below the surface.”

Source: Purdue University

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