While Pluto’s largest moon, Charon, is similar to the dwarf planet in size and in many other ways, it is vastly different from the four smaller satellites that also inhabit the system, according to one of five new studies published in the latest edition of the journal Science.
As Mark Showalter, Senior Scientist at the SETI Institute, and his colleagues explained, Styx, Nix, Kerberos, and Hydra are believed to have formed following the same impact that formed Charon. As such, they expected all of the moons to have similar properties.
What they actually found is the surfaces of the smaller moons are “much brighter and much older than that of their large sibling,” Showalter said in a statement. Furthermore, they found that these moons have unusual rotational characteristics, orbiting around sideways-tilted axes, despite the fact that Pluto’s gravitational tides should have corrected this by now, he added.
The study authors, whose research was based on observations collected by New Horizons during the spacecraft’s flyby of the system eight months ago, believe that collisions from outside objects may have been responsible for causing the odd rotation of Pluto’s four smallest moons.
Research has also led to new discoveries about Pluto, Charon
The dwarf planet’s largest moon was found to have surprises of its own, according to the SETI Institute scientists who published five separate studies based on New Horizons data in the latest issue of Science. For instance, they found evidence of ammonia ice on Charon’s surface.
Top: The surface of Pluto. Bottom: The surface of Charon
Furthermore, the northern regions of its water-rich, icy terrain has a distinctly red hue around the northern region of the moon. The scientists believe that this unusual color is due to tholin, a type of molecule produced by the irradiation of compounds such as methane. On the whole, Charon’s surface is older, more uniform and less geologically active than that of Pluto, they found.
As for the dwarf planet itself, New Horizons data has revealed that it is home to a craterless, ice-rich, 1000 kilometer-wide plain known as Sputnik Planum. The SETI Institute researchers report that this well-known feature is filled with volatile nitrogen and carbon monoxide ices, and based on the relatively smooth texture of the plain, it is likely the site of ongoing geologic activity.
“Among the more puzzling features are the two tall mounds with central depressions that look like volcanoes,” explained Ross Beyer, Senior Scientist at the SETI Institute. “Wright Mons is about 2 miles tall and 90 miles wide, and Piccard Mons is even larger, about 3.5 miles tall and 140 miles across. They could be ice volcanoes, but this will take more analysis to establish.”
The atmosphere of Pluto (Credit: Gladstone et al.)
The spacecraft also helped researchers learn more about the dwarf planet’s atmosphere, added SETI Institute scientist David Hinson. He said that he and his colleagues were “very surprised to observe that Pluto’s atmosphere has a multi-layered bluish haze that extends from the surface to altitudes above 200 km. The upper atmosphere is much colder than expected, which greatly reduces the rate at which it escapes from Pluto. We’ve also measured the surface pressure for the first time – about 11 microbars – and we’ve discovered that the temperature structure of the lower atmosphere varies with location.”
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Image credit: NASA
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