Locations of more than 1,000 craters mapped on Pluto by NASA’s New Horizons mission indicate a wide range of surface ages, which likely means that Pluto has been geologically active throughout its history. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
NASA’s New Horizons science team is discussing >50 exciting discoveries about Pluto at this week’s 47th Annual Meeting of the American Astronomical Society’s Division for Planetary Sciences in National Harbor, Maryland. “The New Horizons mission has taken what we thought we knew about Pluto and turned it upside down,” said Jim Green, director of planetary science at NASA Headquarters, Washington.
Eg NH geologists combined images of Pluto’s surface to make 3D maps that indicate two of Pluto’s most distinctive mountains could be cryovolcanoes—ice volcanoes that may have been active in the recent geological past (10s of miles across and several miles high). Ice volcanoes on Pluto are expected to emit a somewhat melted slurry of substances such as water ice, nitrogen, ammonia, or methane. If Pluto proves to have volcanoes, it will provide an important new clue to itsgeologic and atmospheric evolution. Nothing like this has been seen in the deep outer solar system.
Using New Horizons images of Pluto’s surface to make 3-D topographic maps, scientists discovered that two of Pluto’s mountains, informally named Wright Mons and Piccard Mons, could be ice volcanoes. The color depicts changes in elevation, blue indicating lower terrain and brown showing higher elevation. Green terrains are at intermediate heights. Credit: NASA/JHUAPL/SwRI
Pluto’s surface varies in age—from ancient, to intermediate, to relatively young. To determine the age of a surface area of the planet, scientists count crater impacts. The more crater impacts, the older the region likely is. Crater counts of surface areas indicate it has surface regions dating to just after the formation of the planets of our solar system, 4B yrs ago. But there also is a vast younger area formed in the past 10 million years ie Sputnik Planum, on the left side of Pluto’s “heart” and is completely crater-free in all images received, so far.
The informally named feature Wright Mons, located south of Sputnik Planum on Pluto, is an unusual feature that’s about 100 miles (160 kilometers) wide and 13,000 feet (4 kilometers) high. It displays a summit depression (visible in the center of the image) that’s approximately 35 miles (56 kilometers) across, with a distinctive hummocky texture on its sides. The rim of the summit depression also shows concentric fracturing. New Horizons scientists believe that this mountain and another, Piccard Mons, could have been formed by the ‘cryovolcanic’ eruption of ices from beneath Pluto’s surface. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
New data from crater counts reveal the presence of intermediate, or “middle-aged,” terrains on Pluto, as well. This suggests Sputnik Planum is not an anomaly—Pluto has been geologically active throughout its >4B-year history.
“We’ve mapped more than a thousand craters on Pluto, which vary greatly in size and appearance,” said postdoc researcher Kelsi Singer, SwRI, CO. ” I expect cratering studies like these to give us important new insights into how this part of the solar system formed.”
Crater counts are giving the New Horizons team insight into the structure of the Kuiper Belt itself. The dearth of smaller craters across Pluto and its large moon Charon indicate the Kuiper Belt likely had fewer smaller objects than some models had predicted. So there’s doubt of a longstanding model that all Kuiper Belt objects formed by accumulating much smaller objects —less than a mile wide. The absence of small craters on Pluto and Charon support other models theorizing KBO’s tens of miles across may have formed directly, at current—or close to current—size.
In fact, the evidence that many Kuiper Belt objects could have been “born large” has scientists excited that New Horizons’ next potential target—the 30-mile-wide KBO named 2014 MU69—which may offer the first detailed look at just such a pristine, ancient building block of the solar system.
Pluto’s fascinating system of moons is also revealed. Eg. nearly every other moon in the solar system—including Earth’s moon—is in synchronous rotation, keeping one face toward the planet. This is not the case for Pluto’s small moons.
New Horizons data indicates that at least two (and possibly all four) of Pluto’s small moons may be the result of mergers between still smaller moons. If this discovery is borne out with further analysis, it could provide important new clues to the formation of the Pluto system. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Pluto’s small lunar satellites are spinning much faster, with Hydra—its most distant moon—rotating an unprecedented 89 times during a single lap around the planet. Scientists believe thesespin rates may be variable because Charon exerts a strong torque that prevents each small moon from settling down into synchronous rotation. Pluto’s moons were expected they would wobble, but not to such a degree.
Pluto’s moons behave like spinning tops. Images of Pluto’s 4 smallest satellites also indicate several of them could be the results of mergers of two or more moons. “We suspect from this that Pluto had more moons in the past, in the aftermath of the big impact that also created Charon,” said Showalter.
http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20151109
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