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|Charon(left) and Pluto. Credit: NASA/JHUAPL/SWRI via Getty Images|
| The Cthulhu region of Pluto is seen in this annotated view of the informally named regions of Pluto christened by scientists with NASA’s New Horizons mission.|
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
The scientists said that both Pluto and whatever struck it likely contained simple organic compounds typically found in comets, such as formaldehyde. They also reasoned that these molecules may have made their way into temporary pools of warm liquid water that would likely have existed after the impact melted a significant part of Pluto’s surface.
In lab experiments, the researchers heated soups of water and simple organic compounds such as formaldehyde for many hours. The concentrations of the organic molecules in these solutions were comparable to those found in comets.
The scientists found these soups became darker and redder over time as complex organic compounds formed. After heating for more than 1,000 hours at 122 degrees F (50 degrees Celsius) or greater, they resembled the material in Pluto’s mysterious equatorial dark spots.
In computer simulations, the researchers found that an impactor one-third Pluto’s mass colliding with a Pluto-size object could have generated a Charon-size moon and “warm, liquid-water pools near the equatorial regions of the Pluto-sized object,” said study lead author Yasuhito Sekine, a planetary scientist at the University of Tokyo. (The impact is strong enough to significantly tilt the Pluto-size object, such that the point of impact controls where the dwarf planet’s new equator lies, and the warm pools form along the equator.)
The researchers suggest that in the warm pools of liquid water that would have temporarily existed after the impact, simple organic molecules from either Pluto, the impactor or both could have formed more complex organic materials, such as tholins. Therefore, the Cthulhu region and the other dark reddish spots on Pluto may be “a smoking gun of the giant impact origin of Charon,” Sekine told.
The researchers suggest that high-speed giant impacts may have occurred frequently in the outer regions of the ancient solar system. These collisions may explain the mysterious variety of color, brightness and density seen in large objects in the Kuiper belt, Sekine said.