Dunes on Pluto? On a landscape that already includes soaring ice mountains, smooth plains and strange polygonal patterns, planetary scientists have found another feature that most did not expect of a frozen world.
“We have detected vast fields of features that look like dunes,” said S. Alan Stern, the principal investigator for NASA’s New Horizons spacecraft, which flew past Pluto on July 14. “Now we are being careful to say they look like dunes. They may or may not actually be dunes.”
That surprise is among several in a new batch of flyby photographs released by NASA.
Dunes are undulating ridges of particles piled up by blowing wind, but the air of present-day Pluto is much too thin and weak to sculpt the fields of dunes, some of which stretch for kilometers. That could suggest that Pluto once possessed a much thicker atmosphere. If they are not dunes, then some force other than wind created them. “Their origin is under debate,” Stern said.
It is also unknown whether the dunelike structures are made of ice particles or sandlike bits of rock. Some of the structures are fairly bright, reflective as ice might be; others are very dark.
“The dunes may all be identical in composition,” Stern said, “but some may have a veneer of dark stuff on them. Or they may be different. We just don’t know.”
New Horizons captured a trove of images and data during the flyby, but it will take a year for it to send all that information across the solar system for scientists to study. In August, the spacecraft sent back data from two instruments measuring the dance of charged particles around Pluto and a student experiment that counted dust particles.
The scientists working with the charged particles data say they do not yet understand what they have found.
“Because, as you might expect from a first flyby, they found really puzzling things,” Stern said. “They know they got good data, and they see signatures from the Pluto system, but they’re not anything like they predicted.”
The mission team has resumed the retrieval of images from New Horizons and plans to release them weekly. Other photographs in the most recent batch show multiple haze layers in Pluto’s atmosphere, glacierlike flows of ice and what Stern described as “a very disorganized region hundreds of miles across where the mountains appear to be chaotically jumbled.”
Similar jumbled landscapes have been seen on Jupiter’s moon Europa, where the flow of water in an underground ocean may have destabilized the surface. Stern said on Pluto, it is possible that liquid nitrogen below the surface caused the mountains to collapse.
This region “is going to be a high-priority place for study in the future,” Stern said. “It’s going to tell us about the interior and the history of the interior.”
In late October and early November, New Horizons is set to fire its thrusters four times to point itself toward its next destination: a small, icy body designated 2014 MU69, which it will study in 2019 if NASA approves an extension to the mission.