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Pluto has dune-like ridges beside Sputnik Planitia, and the leading explanation is that methane-ice grains were moved by wind. New Horizons photographed the patterns during its 2015 flyby; their shape and scale support a dune interpretation, but neither the grains nor their movement were directly sampled. Sublimation—ice turning directly into gas—may also help move particles, and erosion by sublimation remains an alternative or contributing explanation.
Where are Pluto’s dunes?
The ridges lie near the mountains along the western edge of Sputnik Planitia, Pluto’s broad, bright basin. NASA describes dune fields extending for at least 75 kilometers along that edge. New Horizons’ 2015 flyby provided the images that revealed the repeating patterns.
NASA identifies nearby water-ice mountains as possible source terrain for material that could feed the fields. That does not mean the dune grains themselves are thought to be water ice: the 2018 dune study found that methane ice best explains the observed ridge spacing.
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The key clue is the ridges’ wavelength—the distance between repeating features. The 2018 study, Dunes on Pluto, reported a wavelength of approximately 0.4–1 kilometer. Its analysis found that this scale is best explained by grains about 200–300 micrometers across, with methane ice as the material, transported under moderate winds below 10 meters per second.
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These are inferred properties from the observed patterns and the study’s interpretation, not results from a sample collected on Pluto. New Horizons did not directly examine or retrieve dune grains.
How could wind move grains in Pluto’s thin atmosphere?
In the dune interpretation, wind is the main transport mechanism: it moves loose grains and helps form the repeated ridges. The study’s proposed moderate winds are below 10 meters per second. NASA’s 2020 overview separately describes winds of no more than 20 miles per hour and notes that past winds may have been stronger when Pluto’s atmosphere was thicker. Those figures come from different descriptions; they should not be treated as competing direct measurements of wind at the dunes.
Sublimation may assist transport. As surface ice turns directly into gas, it may help lift or dislodge grains, making them easier for wind to move. The available interpretation does not establish exactly how much this process contributes.
Are Pluto’s dunes definitely made of methane ice?
Methane ice is the best-supported explanation for the grains in the 2018 study, but it is an inference rather than a confirmed composition from direct sampling. The visible ridges might also be patterns carved by sublimation erosion, or the result of both particle movement and erosion. Jeffery Moore, a study author and research scientist at NASA’s Ames Research Center, described the patterns as dune-like while explicitly preserving those alternatives in NASA’s June 9, 2018 account.
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How old are the formations?
NASA characterized the formations as young in geological terms, on the scale of decades or centuries. This is a broad estimate, not a precise date assigned to individual ridges.
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