It's a depression with a peak in the middle, and it looks to be about 50 metres across. NASA calls the strange feature "captivating."
The U.S. space agency is set to release more close-ups of Pluto and its moons at a media briefing at 1 p.m. ET Friday. It will be live streamed on CBCNews.ca.
The first images from the flyby, released yesterday, already revealed some surprises, including mountains on Pluto and canyons on Charon.
The newest image was captured by New Horizons when it was about 79,000 kilometres from Charon, about 1½ hours before its closest approach to Pluto this past Tuesday.
That was the day New Horizons became the first spacecraft to make a flyby of Pluto and its moons, capturing 1,600 images in the process.
It will take 16 months for the spacecraft, which is currently about 4.8 billion kilometres from Earth, to send all its images and data back to Earth.