Ever since the New Horizons spacecraft flew by Pluto in July 2015, people here at Earth have been treated to an endless supply of discoveries about the dwarf planet. These included the first accurate pictures of what Pluto looks like, images of “Pluto’s Heart“, information about the geology and morphology of the surface (and its largest moon, Charon), and information about Pluto’s atmosphere and its escape rate.
And based on the data obtained from images by the New Horizons probe, NASA recently announced that Pluto’s flowing glaciers have numerous hills composed of water ice floating on top of them. Located in the vast ice plain known as “Sputnik Planum” – named after Sputnik One, the first satellite to orbit Earth – these hills measure several kilometers across, and are believed to be fragments that originated from the surrounding uplands.
The presence of flowing ice on Sputnik Planum was confirmed back in July of 2015, thanks to data obtained by New Horizons’ Long-Range Reconnaissance Imager (LORRI). Located in the western portion of the heart-shaped region known as Tombaugh Regio, this flowing ice was determined to be the result of recent geological activity.
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Since these hills are composed of water ice, which is less dense than nitrogen ice, scientists believe they are essentially adrift in a sea of frozen nitrogen. And since these ice floes behave much like glaciers here on Earth, it is believed that the hills are fragments from the rugged western portion of Tombaugh Regio. These would have then broken off, and are now being carried slowly along by the nitrogen glaciers into Sputnik Planum.
These hills eventually cluster into groups that reach up to 20 km across once they reach the central terrain of Sputnik Planum, where they become subject to the convective motions of the nitrogen ice. Along with the presence of youthful mountains in the heart-shaped region that are 3,500 meters (11,000 feet) in height, these hills are yet another example of Pluto’s abundant geological activity.
As Dr. Alan Stern – the Principal Investigator of the New Horizons Science Team and a Professor at the Southwest Research Institute – told Universe Today via email: “The floating hills of Pluto are unlike anything seen in the outer solar system before, and they remind us once again that small planets have seemed to created geologies as complex as on the terrestrial planets.”
The image of these hills (shown at top) was captured by New Horizons’ Multispectral Visible Imaging Camera (MVIC) instrument on July 14th, 2015, about 12 minutes before the spacecraft made its closest approach to Pluto. The image covers an area that measured about 500 long and 310 km wide (300 by 210 mi), with hill chains appearing at the southern end.
At the northern end of the image, a particularly large accumulation of hills composed of water ice was discerned. This formation has been named Challenger Colles (in honor of the crew of the space shuttle Challenger) and measures 60 by 30 km (37 by 22 mi). Scientists believe this formation may have become immobilized due to the nitrogen ice being particularly shallow in the area.
Geological activity was something NASA scientists were hoping to find on Pluto, but didn’t expect. Along with other findings, the discovery of these floating ice hills have led scientists to realize just how complex Pluto’s geology activity really is. All told, the planet shows signs of surface ice convection, wind streaks, volatile transport, glacial flow, and cryovolcanism.
One can only imagine what else they might find as the New Horizons team continues to pour over the data obtained from this historic encounter.
Further Reading: NASA