The closeups of Nix and Hydra were captured by the first ever flyby of Pluto and its moons by the New Horizons spacecraft last week and released by NASA today.
Nix is a jelly bean-shaped moon about 42 kilometres long and 36 kilometres wide. A new enhanced colour image shot by the spacecraft from 165,000 kilometres away shows a reddish region with "hints of a bull's eye pattern" that scientists suspect to be a crater.
"This observation is so tantalizing, I'm finding it hard to be patient for more Nix data to be downlinked," said mission scientist Carly Howett of Southwest Research Institute in a statement.
The data yet to be sent from the spacecraft includes chemical information about what Nix is made of that is expected to show why that region is so red.
Hydra is about 55 kilometres long and 40 kilometres wide. A new black and white image captured from about 231,000 kilometres away shows a variety of features, including two very large craters, including one that is mostly in shadow.
"Before last week, Hydra was just a faint point of light, so it's a surreal experience to see it become an actual place, as we see its shape and spot recognizable features on its surface for the first time," said Ted Stryk, a mission science collaborator at Roane State Community College in Tennessee.
'Spectacular' images coming Friday
Jim Green, director of NASA's planetary sciences division, said a bunch of new images from New Horizons will be released at a news conference that begins at 2 p.m. Friday.
"It'll be pretty spectacular," he told CBC News in a phone interview Tuesday.
During the historic flyby on July 14, New Horizons came within 12,392 kilometres of Pluto's surface, capturing plains and mountains on the surface of the dwarf planet.
Closeups of Pluto's largest moon Charon have shown huge canyons and a mysterious mountain growing out of a moat-like depression.
Pluto has five moons. Photos of the two remaining moons, Styx and Kerberos, are expected to be sent to Earth within the next few months.