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When NASA’s New Horizons space probe, after traveling all the way out to Pluto, sent back photos of that former planet, the most striking feature was a heart-shaped region that covers a large portion of the body. (The feature is approximately 1200 km by 2000 km, approximately one quarter of the area of the United States.) Popular culture responded to the image of the heart on Pluto with all sorts of romantic memes, but for scientists, the significant question was: What is this heart-shaped feature, and how did it form? A new report provides an answer to these questions.
After performing simulations, the researchers assert that the most likely origin of the heart (it’s formal name is the Tombaugh Regio) is it was produced by a collision with another body, but the relative velocity of the collision was low, and the angle of collision was oblique. The elongated shape of the feature is consistent with an oblique impact. Further, the speeds of moving bodies at the edge of the Solar System are much lower than planets or other bodies that are close to the Sun (such as Earth). As such, a low-speed impact is probable. It is thought that the body Pluto collided with was perhaps 700 km in diameter. The heart is covered by nitrogen ice, which is why the heart has a lighter color than the rest of the dwarf planet; solid nitrogen reflect light more efficiently than other substances found on the surface of Pluto.
However, researchers were puzzled as to why the feature hadn’t migrated to one of Pluto’s poles rather than hanging out near the equator. Tombaugh Regio is a depression on the surface of Pluto, and on a rotating body with a liquid subsurface, equatorial regions will tend to bulge out. Under these assumptions, the poles are a much more stable location for a surface depression. However, this study demonstrated that Pluto does not have a liquid subsurface, and the event of the collision that made the heart didn’t even melt much of Pluto’s surface. Pluto is so cold that everything on it, and in it, is frozen solid. So as a result, the heart is perfectly stable on the equator.
So now we know a little bit more about Pluto and its most identifiable feature.
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