USA TODAY US Edition
Scientists learn why Mordor mars Pluto moon
On the outskirts of the solar system lies an icy little moon called Charon with a mysterious blemish: a great dark blotch the color of a dried bloodstain.
The blotch, nicknamed Mordor after J.R.R. Tolkien’s forbidding “dark land” in The Lord of the
Rings, is the subject of much speculation. Now scientists think they know why it’s there. Researchers say in this week’s
Nature that Mordor was born of material purloined from the nearby dwarf planet Pluto. As Pluto’s atmosphere drifts into space, some of the escaping molecules are captured by Charon and eventually transformed into dark-red chemicals — a phenomenon seen nowhere else in the solar system, says Laurence Trafton, an astronomer at the University of Texas-Austin who was not involved with the study.
The mystery of Mordor began last year, when the New Horizons spacecraft became humanity’s first ambassador to Pluto.
As the spacecraft approached its target, scientists saw “this persistent dark spot at the top of Charon … (that) never went away,” says Will Grundy, study co-author and a scientist at Arizona’s Lowell Observatory. “We were all scratching our heads.”
Perhaps the dark blotch stemmed from the same geological events that carved out Charon’s ridges and canyons. Or perhaps Mordor formed from chemicals from Pluto that got trapped on Charon’s icy surface.
Grundy and his colleagues calculated the temperature on Charon during its winter. They found Charon’s north pole stays “ridiculously cold” for decades, Grundy says — about -415 degrees Fahrenheit or below from the mid-1800s to the late 1980s.
That’s cold enough, and long enough, for molecules that drift away from Pluto’s atmosphere to freeze onto Charon’s north pole.