The latest and greatest views from NASA's New Horizons probe reveal what could be dimpled terrain on dwarf planet Pluto — and bright craters on Charon, its biggest moon.
The new imagery was captured Wednesday from a distance of about 3.7 million miles (6 million kilometers). It shows Pluto's heart-shaped bright area passing out of view on the right edge of its disk, a dark equatorial streak known as "the whale" stretching across the bottom, and a mysterious sliver of light material peeking from beneath the whale.
This picture also shows subtle surface variations above the whale — variations that suggest the dimpled "cantaloupe terrain" of Neptune's largest moon, Triton. Scientists say Triton could have been a world from Pluto's cosmic neighborhood that was snared by Neptune's gravitational field as it was passing by. Sharper images should reveal whether there's truly a family resemblance.
Meanwhile, New Horizons' view of Charon continues to show a dark circular area at one of its poles — plus bright areas that may be impact craters. That's a welcome sight for geologists.
"It will help us see what's hidden beneath the surface," Jeff Moore of NASA's Ames Research Center, leader of the mission's geology, geophysics and imaging team, said Thursday in a news release. "Large craters can excavate material from several miles down and reveal the composition of the interior."
The color imagery shows that Pluto's surface has a reddish cast, due to the presence of organic compounds known as tholins, while Charon is a wan gray color because it's covered with frozen water and ammonia compounds.
"These two objects have been together for billions of years, in the same orbit, but they are totally different," said the mission's principal investigator, Alan Stern of the Southwest Research Institute.
Every hour brings New Horizons another 30,000 miles (50,000 kilometers) nearer to next Tuesday's flyby. To keep track of the mission, follow @NASANewHorizons and @NewHorizons2015 on Twitter, visit the websites maintained by NASA and the New Horizons science team, and keep tabs on DailyPluto.com on Facebook.