NASA's New Horizons mission has revealed that Pluto's largest moon, Charon, is full of surprises, including a strange feature that scientists are calling "a mountain in a moat."
You can see it in the upper left corner of the inset in the image above.
"This is a feature that has geologists stunned and stumped," Jeff Moore, who leads New Horizons' Geology, Geophysics and Imaging team, said in a statement.
A deep gash that scientists say is longer and deeper than the Grand Canyon is visible at the top right of Charon's globe.
The spacecraft took the image early Tuesday morning, just 1.5 hours before its closest approach to Pluto. The craft was about 49,000 miles from the surface of Charon at the time.
The picture shows an area of the moon about 200 miles from top to bottom, or about the distance between Los Angeles and San Luis Obispo.
The first batch of observations from New Horizons' close brush with the Pluto system was sent down Wednesday morning, and planetary scientists are still poring over the data.
These early images were sent in a compressed state to ensure the highest priority data gets down safely. Sharper versions will be sent down over the next 16 months as the spacecraft slowly beams all of its raw data across the solar system. There will be hundreds more images of the dwarf planet and its largest moon to view.
But even these early glimpses of Charon have defied scientists' expectations.
"We originally thought Charon would be an ancient terrain covered in craters," said New Horizons team member Cathy Olkin. "So when we saw the pictures this morning, it just blew our socks off."
Although there are craters visible on Charon's surface, there are not nearly as many as scientists had thought, and that suggests that Charon has been geologically active in the relatively recent past.
"We've been saying Pluto didn't disappoint, and now I can say Charon didn't disappoint either," Olkin said Wednesday.
Measurements made by New Horizons reveal that Charon is 750 miles across. That's slightly more than half of the diameter of Pluto, which is only 1,473 miles across.
The two bodies make up the only binary planet in our solar system. Instead of the moon orbiting around the dwarf planet, Charon and Pluto orbit around a center of gravity between the two bodies.
New images of Pluto are expected to be released Friday.