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The most recognizable feature on Pluto is its \u201cheart,\u201d a relatively bright valentine-shaped area known as Tombaugh Regio. How that heart got started is one of the dwarf planet\u2019s deepest mysteries \u2014 but now researchers say they\u2019ve come up with the most likely scenario, involving a primordial collision with a planetary body that was a little more than 400 miles wide.<\/p>\n
The scientific term for what happened, according to a study published today in Nature Astronomy, is \u201csplat.\u201d <\/p>\n
Astronomers from the University of Bern in Switzerland and the University of Arizona looked for computer simulations that produced dynamical results similar to what\u2019s seen in data from NASA\u2019s New Horizons probe. They found a set of simulations that made for a close match, but also ran counter to previous suggestions that Pluto harbors a deep subsurface ocean. They said their scenario doesn\u2019t depend on the existence of a deep ocean \u2014 which could lead scientists to rewrite the history of Pluto\u2019s geological evolution.<\/p>\n
<\/p>\n University of Arizona astronomer Adeene Denton, one of the study\u2019s co-authors, said the formation of the heart \u201cprovides a critical window into the earliest periods of Pluto\u2019s history.\u201d<\/p>\n \u201cBy expanding our investigation to include more unusual formation scenarios, we\u2019ve learned some totally new possibilities for Pluto\u2019s evolution,\u201d Denton said in a news release. Similar scenarios could apply to other objects in the Kuiper Belt, the ring of icy worlds on the edge of our solar system.<\/p>\n The study focuses on the left half of the heart, a 1,250-mile-long, teardrop-shaped region called Sputnik Planitia. That region contains an assortment of ices and is roughly 2.5 miles lower in elevation than the rest of Pluto. It\u2019s clearly the result of a massive impact.<\/p>\n \u201cWhile the vast majority of Pluto\u2019s surface consists of methane ice and its derivatives, covering a water-ice crust, the Planitia is predominantly filled with nitrogen ice which most likely accumulated quickly after the impact due to the lower altitude,\u201d said study lead author Harry Ballantyne, a research associate at the University of Bern. <\/p>\n The eastern half of the heart is covered by a similar but much thinner layer of nitrogen ice. The origins of that part of Tombaugh Regio are still unclear, but it\u2019s probably related to the processes that shaped Sputnik Planitia.<\/p>\n Ballantyne and his colleagues ran a wide assortment of computer simulations for the ancient impact. Those simulations reflected a range of sizes and compositions for the impacting body, at different velocities and angles of approach. The best fit for Sputnik Planitia\u2019s shape involved a 400-mile-wide object, composed of 15% rock, coming in at an angle of 30 degrees and hitting Pluto at a relatively low velocity.<\/p>\n Based on those parameters, the object would have plowed through Pluto\u2019s surface with a splat. The resulting shape wouldn\u2019t look like your typical impact crater. Instead, it would look like a bright, icy teardrop, with the rocky core of the impacting body ending up at the tail of the teardrop.<\/p>\n \u201cPluto\u2019s core is so cold that the rocks remained very hard and did not melt despite the heat of the impact, and thanks to the angle of impact and the low velocity, the core of the impactor did not sink into Pluto\u2019s core, but remained intact as a splat on it,\u201d Ballantyne explained.<\/p>\n \n