by Amy Lynn
When the world laid eyes on Pluto for the first time back in July, everyone expected to see a “lifeless” icy world. So you can imagine the surprise when we saw evidence instead that indicated Pluto and Charon were geologically active. Four months later, we are just beginning to comprehend this enigmatic, icy world.
One of the greatest accomplishments so far for New Horizons’ geology team is the creation of high-quality 3-D topographical maps. After analyzing the maps, the team discovered two very distinctive mountains near Pluto’s south pole. Further analysis indicates these two mountains may have been active in the recent geological past and could be cryovolcanoes — volcanoes that spew ice instead of lava.
Newly released NASA images show the two mountains, informally named Wright Mons and Piccard Mons, are very broad. They measure up to 160 kilometers across. Piccard Mons towers as high as 6 kilometers (3.5 miles) above the surface and is located just beyond the day/night boundary, so the only images we have of it are taken in twilight. Wright Mons is only 3-5 kilometers high (2 miles), and both mountains are roughly circular in shape with a deep depression at their summit — much like the shield volcanoes we see here on Earth.
These mountains are very similar to volcanic features we see on the inner terrestrial planets. However, unlike their terrestrial analogs, these volcanoes would spew a melted slurry of water ice, ammonia and methane instead of molten rock. If these prove to be the icy volcanoes scientists believe them to be, this would be one of the most significant discoveries made by New Horizons as nothing like this has ever been observed in the outer Solar System. Sure Enceladus has icy plumes, but the ejected material is coming from cracks in the moon’s surface, not from active volcanoes.
The team is not officially calling them cryovolcanoes just yet, as further research is needed. However, Oliver White New Horizons postdoctoral researcher at NASA’s Ames Research Center in California said during a press conference, “ When you see a mountain with a big hole in the top, you think only one thing. And as someone who did their PhD research in volcanic morphology, I can’t unsee volcanoes.”
Alan Stern expanded upon the volcano talk by saying, “The nearest neighbor analogy to these constructs is on Mars. There’s nothing like them on any body in between. It’s truly amazing.” The team doesn’t know what they are made out of just yet, but if they are volcanic then the summit depressions would have formed after material beneath the surface drained away.
Along with the presence of potential cryovolcanoes, scientists were surprised to find that Pluto has a very long history of geologic activity with varying surface ages — ranging from ancient to middle-aged to geologically young.
In order to determine the age of a particular region, the team counted the number of crater impacts. A larger number of impacts signals an older region. Pluto has over 1,000 craters on its surface, indicating that some areas date back to a time just after the planets formed some four billion years ago. At the same time, other areas like the smooth icy plains of Sputnik Planum are only about 10 million years old, meaning geologically speaking it was “born yesterday”. The absence of craters in this region suggest that Pluto has been active throughout much of its four billion year history. Dr. Kelsi Singer of the Southwest Research Institute explained during the session, “Pluto is giving us a new view of how small planets evolve.”
Singer went on to say, “We’ve mapped more than a thousand craters on Pluto, which vary in size and appearance. Among other things, I expect cratering studies like these to give us important new insights into how this part of the Solar System formed.”
So, what is driving all this activity? Scientists believe that the activity we see is a result of an internal heat source — like the radioactive decay of elements left over from the formation of Pluto over 4.5 billion years ago are keeping the interior warm enough for ice to flow. With a surface covered in volatile ices, it doesn’t take as much heat as it would for molten rock. Due to the nature of exotic ices, you get more bang your buck with less heat.
So far New Horizons and Pluto have put on quite a show for us, but this is only the beginning. With only 20 percent of the data downloaded so far, we have many more months of exciting data to look forward to.
