Pluto's major moon Charon has a bizarre red patch (similar to a bloodstain) on one of its polar regions. In a new study, scientists have finally been able to explain this mysterious dark patch.

This reddish colored patch was first observed by NASA's New Horizons mission scientists last year, who named it Mordor Macula. Mordor Macula is a sinister region in the fantasy fiction of J.R.R. Tolkien's Lord of the Rings.

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During the first-ever mission to Pluto which included a flyby of the dwarf planet, scientists observed a persistent dark spot on top of Charon, the co-author of the study, Will Grundy from Arizona's Lowell Observatory, said.

Mordor was apparently caused by a special material originating from the icy, dwarf planet. Since Pluto's atmosphere has become tenuous and Charon is so close to its binary planet, some molecules escaped and transformed into dark reddish hued chemicals, according to astronomer Laurence Trafton of the University of Texas. This phenomenon has not been seen elsewhere in the solar system.

Scientists initially thought that this dark patch originated from geological events that also formed the ridges and canyons of Charon or some chemicals trapped within Charon's icy surface.

In this new study, scientists calculated temperatures on Charon, especially during its long, dark winter period. Charon's northern pole is so frigid, and it has been that way for decades, plummeting to way below -415 degrees Fahrenheit starting from the 1800s to the late 1980s.

Scientists have suggested that this kind of temperatures along with molecules escaping from Pluto's atmosphere--transferring and freezing onto Charon's north pole--are the most likely culprits for this distinct red hue.

This new study has been published in the journal, Nature.