Planetary researchers working with data from NASA’s New Horizons and ESA’s Rosetta missions have developed a new theory for the formation of the dwarf planet Pluto. Their paper will be published in the October 2018 issue of the journal Icarus (arXiv.org preprint).
This high-resolution image of Pluto was taken by New Horizons on July 14. Pluto’s surface sports a remarkable range of subtle colors, enhanced in this view to a rainbow of pale blues, yellows, oranges, and deep reds. Many landforms have their own distinct colors, telling a complex geological and climatological story that scientists have only just begun to decode. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
“We’ve developed what we call ‘the giant comet’ cosmochemical model of Pluto formation,” said Dr. Christopher Glein, of the Space Science and Engineering Division at Southwest Research Institute.
At the heart of the research is a nitrogen-rich ice sheet in a near-equatorial region called Sputnik Planitia, which constitutes the western lobe of Pluto’s heart’ (Tombaugh Regio).
“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/Churyumov-Gerasimenko, the comet explored by the Rosetta orbiter,” Dr. Glein said.
In addition to the comet model, he and his colleague, Southwest Research Institute program director Dr. J. Hunter Waite Jr., also investigated a solar model, with Pluto forming from very cold ices that would have had a chemical composition that more closely matches that of the Sun.
The duo needed to understand not only the nitrogen present at Pluto now — in its atmosphere and in glaciers — but also how much of the volatile element potentially could have leaked out of the atmosphere and into space over the eons.
They then needed to reconcile the proportion of carbon monoxide to nitrogen to get a more complete picture.
Ultimately, the low abundance of carbon monoxide at Pluto points to burial in surface ices or to destruction from liquid water.
Sputnik Planitia basin: this scene, which is about 250 miles (400 km) across, uses data from New Horizons’ Ralph/MVIC instrument. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
“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,” Dr. Glein said.
“However, the solar model also satisfies some constraints.”
While the research pointed to some interesting possibilities, many questions remain to be answered.
“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,” Dr. Glein said.
“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.”
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Christopher R. Glein & J. Hunter Waite Jr. 2018. Primordial N2 provides a cosmochemical explanation for the existence of Sputnik Planitia, Pluto. Icarus 313: 79-92; doi: 10.1016/j.icarus.2018.05.007
