Previous reports suggested that Pluto's iconic heart-shaped region was formed when it was hit by an asteroid about the size of Manhattan sometime in its troubled past. Now, astronomers theorized that the heavy nitrogen ice-filled and crater-free "heart" caused the entire dwarf planet to tip over to its side.

Astronomers called the iconic heart-shaped region Tombaugh Regio, and it is one of the biggest and most surprising discoveries that NASA's New Horizons probe beamed back last year.

Tombaugh Regio's west side is the crater-free region called Sputnik Planum. Researchers found that this area's central crater is very close to the planet's tidal axis or the imaginary line that links Pluto to its largest companion, Charon.

When a planet and its moon are tidally locked, they show each other the same face as they rotate. Romanticism aside, the incidence is too great to be just a coincidence.

During the Lunar and Planetary Science conference in Texas last month, two research teams provided a hypothesis. They theorized that if the ice-cold Sputnik Planum is denser than the rest of the planet on average, Charon's pull would be greater, causing the entire planet to tip on its side and towards it. And isn't that just darned romantic?

"Charon is going to try to pull it into the tidal axis - that just happens to be where you would minimize the energy," said James Keane from the University of Tuscon, Arizona and one of the team leaders.

The nitrogen ice that built on top of the Sputnik Planum's crater is believed to be a kilometer thick (0.62 miles). While the region is essentially a crater, the sheer mass of the nitrogen ice made up for its density.

The teams believed that in the span of millions of years, the heart shifted either hundreds or even thousands of kilometers from its original location.

While more research is needed to confirm this theory, one thing is for certain - we have more to learn about Pluto and its heart-shaped, crater-free and icy region. As astronomers delve deeper into Pluto's New Horizons images, we're excited to know more about its traumatic, romantic past.

Photo: NASA/APL/SwRI | Flickr

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