Researchers on the New Horizons team have released a set of five scientific papers describing results from the July 2015 flyby of the Pluto system.
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.
“These five detailed papers completely transform our view of Pluto – revealing the former ‘astronomer’s planet’ to be a real world with diverse and active geology, exotic surface chemistry, a complex atmosphere, puzzling interaction with the Sun and an intriguing system of small moons,” said New Horizons principal investigator Dr. Alan Stern, from the Southwest Research Institute.
In the first of the five papers, published this week in the journal Science, Dr. Jeffrey Moore from NASA’s Ames Research Center and co-authors offer some of the first descriptions of the wide array of geological features on Pluto and its largest moon, Charon.
The scientists report evidence of tectonics, glacial flow, transport of large water-ice blocks, and broad mounds on the dwarf planet – possibly a result of cryovolcanoes.
Data on the variability of terrain suggests the dwarf planet has been frequently resurfaced by processes like erosion, pointing to active geomorphic processes within the last few hundred million years.
Such processes have not been active so recently on Charon; divided into a rugged north and a smooth south, the moon is marked with older craters and troughs, contrasting with Pluto.
“Observing Pluto and Charon up close has caused us to completely reassess thinking on what sort of geological activity can be sustained on isolated planetary bodies in this distant region of the Solar System, worlds that formerly had been thought to be relics little changed since the Kuiper Belt’s formation,” Dr. Moore said.
In a second study, Dr. Will Grundy of the Lowell Observatory and his colleagues analyze the colors and chemical compositions of the icy surfaces of Pluto and Charon.
The volatile ices, including water ice and solid nitrogen, that dominate Pluto’s surface are distributed in a complicated way — a result of geomorphic processes acting on the surface over different seasonal and geological timescales. Broad expanses of reddish-brown molecules called tholins accumulated in some parts of Pluto.
“We see variations in the distribution of Pluto’s volatile ices that point to fascinating cycles of evaporation and condensation,” Dr. Grundy said. “These cycles are a lot richer than those on Earth, where there’s really only one material that condenses and evaporates – water.”
“On Pluto, there are at least three materials, and while they interact in ways we don’t yet fully understand, we definitely see their effects all across Pluto’s surface.”
In a third study, Dr. Fran Bagenal from the University of Colorado, Boulder, and co-authors report how Pluto modifies its space environment, including interactions with the solar wind and a lack of dust in the system.
“We’ve discovered that pre-New Horizons estimates wildly overestimated the loss of material from Pluto’s atmosphere,” Dr. Bagenal said.
“The thought was that Pluto’s atmosphere was escaping like a comet, but it is actually escaping at a rate much more like Earth’s atmosphere.”
“We’ve discovered that methane, rather than nitrogen, is Pluto’s primary escaping gas,” added Dr. Randall Gladstone of the Southwest Research Institute, lead author of the fourth study. “This is pretty surprising, since near Pluto’s surface the atmosphere is more than 99% nitrogen.”
In their study, Dr. Gladstone and co-authors investigate the atmosphere of Pluto, which is colder and more compact than expected and hosts numerous extensive layers of haze.
Finally, Dr. Hal Weaver from the Johns Hopkins University Applied Physics Laboratory and co-authors examine Pluto’s small moons — Styx, Nix, Kerberos and Hydra.
According to the scientists, the four moons range in diameter from about 25 miles (40 km) for Nix and Hydra to about 6 miles (10 km) for Styx and Kerberos.
They observed that the moons have highly anomalous rotation rates and uniformly unusual pole orientations, as well as icy surfaces with brightness and colors distinctly different from those of Pluto and Charon.
They’ve found evidence that some of the moons resulted from mergers of even smaller bodies, and that their surface ages date back at least 4 billion years.
“These latter two results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary system,” Dr. Weaver said.
Taken together, these results from the flyby of the Pluto system pave the way for scientists’ better understanding of processes of planetary evolution.
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Jeffrey M. Moore et al. 2016. The geology of Pluto and Charon through the eyes of New Horizons. Science, vol. 351, no. 6279; doi: 10.1126/science.aad7055
W.M. Grundy et al. 2016. Surface compositions across Pluto and Charon. Science, vol. 351, no. 6279; doi: 10.1126/science.aad9189
F. Bagenal et al. 2016. Pluto’s interaction with its space environment: Solar wind, energetic particles, and dust. Science, vol. 351, no. 6279; doi: 10.1126/science.aad9045
G. Randall Gladstone et al. 2016. The atmosphere of Pluto as observed by New Horizons. Science, vol. 351, no. 6279; doi: 10.1126/science.aad8866
H.A. Weaver et al. 2016. The small satellites of Pluto as observed by New Horizons. Science, vol. 351, no. 6279; doi: 10.1126/science.aae0030
