According to astronomers from the Southwest Research Institute (SwRI), Pluto might have a slightly different formation history than previously thought. The dwarf planet might be the end product of a huge number of comets colliding and merging into a single object.
The idea comes from an analysis of the chemical composition of Pluto from NASA’s New Horizons, which visited the object in 2015, and ESA’s Rosetta mission that studied comet 67P/Churyumov-Gerasimenko. The team showed that the abundance of nitrogen in Sputnik Planitia, the heart-shaped glacier of Pluto, is consistent with a cometary origin. Their work is reported in Icarus.
“We’ve developed what we call ‘the giant comet’ cosmochemical model of Pluto formation,” co-author Dr Christopher Glein, from SwRI’s Space Science and Engineering Division, said in a statement. “We found an intriguing consistency between the estimated amount of nitrogen inside the glacier and the amount that would be expected if Pluto was formed by the agglomeration of roughly a billion comets or other Kuiper Belt objects similar in chemical composition to 67P, the comet explored by Rosetta.”
The team also investigated a different, more traditional model, where the formation of Pluto came from very cold ice that formed in the primordial Solar Nebula. The solar model can explain certain features of the dwarf planet that's not explained by the giant comet model, and vice-versa. The team believes that they have barely scratched the surface of the evolution of Pluto.
“This research builds upon the fantastic successes of the New Horizons and Rosetta missions to expand our understanding of the origin and evolution of Pluto,” explained Glein. “Using chemistry as a detective’s tool, we are able to trace certain features we see on Pluto today to formation processes from long ago. This leads to a new appreciation of the richness of Pluto’s ‘life story,’ which we are only starting to grasp.”
The models cannot explain the comparative abundance of nitrogen and other molecules, such as carbon monoxide. The planetary scientists think that it might have been buried deeper in the planet or maybe modified during the planet's evolution.
“Our research suggests that Pluto’s initial chemical makeup, inherited from cometary building blocks, was chemically modified by liquid water, perhaps even in a subsurface ocean,” Glein added.
This is just the beginning of this discussion. A lot more will need to be known about Pluto before we can tell how it came to be. On January 1, 2019, New Horizons will fly over MU69, another Kuiper Belt object, and that might help us understand how the further members of the Solar System formed.