Pluto 'Totally Different' from Big Moon Charon, New Photos Show

Pluto and Charon in Color, July 8, 2015
This image of Pluto (right) and Charon, taken by NASA’s New Horizons spacecraft on July 8, 2015, combines a view captured by the probe’s long-range camera with color information obtained earlier in the mission from the Ralph instrument. (Image credit: NASA-JHUAPL-SWRI)

New photos by NASA's approaching New Horizons probe capture Pluto and its largest moon, Charon, in fascinating detail.

The new images —  which were taken late Wednesday (July 8) from a distance of 3.7 million miles (6 million kilometers) — show that Pluto and Charon are very different bodies, though they circle a common center of gravity and are separated by a mere 12,200 miles (19,640 km), NASA officials said.

"These two objects have been together for billions of years, in the same orbit, but they are totally different," New Horizons principal investigator Alan Stern, of the Southwest Research Institute (SwRI) in Boulder, Colorado, said in a statement. [New Horizons Probe's July 14 Pluto Flyby: Complete Coverage]

New Horizons’ Long Range Reconnaissance Imager (LORRI) captured Pluto on July 8, 2015. The bright edge below the dark “whale” is real, not the result of image processing. (Image credit: NASA-JHUAPL-SWRI)

At 750 miles (1,200 km) in diameter, Charon is about half was wide as Pluto itself. The two bodies' center of mass lies outside the dwarf planet, so many researchers regard Pluto-Charon as a binary system. (Pluto has four other moons — Nix, Hydra, Kerberos and Styx — all of which are tiny.)

Most scientists think the dwarf planet system was shaped long ago by a huge collision between a proto-Pluto and and proto-Charon. Those two objects were apparently quite different from each other, based on the characteristics of modern Pluto and modern Charon.

For example, Pluto sports a reddish-orange hue, while Charon is quite gray. And New Horizons' observations leading up to its epic July 14 Pluto flyby have already shown that the dwarf planet's surface is a complex blend of bright and dark features, including one marking that looks like a giant heart and another that mission team members have dubbed "the whale." Meanwhile, Charon is more uniform (with the notable exception of a mysterious dark polar cap).

The new photos reveal light patches on Charon that might be craters, mission team members said.

This image of Charon was obtained by New Horizons’ Long Range Reconnaissance Imager (LORRI) on July 8, 2015. (Image credit: NASA-JHUAPL-SWRI)

"If we see impact craters on Charon, it will help us see what's hidden beneath the surface," Jeff Moore, of NASA's Ames Research Center in Moffett Field, California, said in the same statement.

"Large craters can excavate material from several miles down and reveal the composition of the interior," added Moore, who leads New Horizons' geology, geophysics and imaging (GGI) team.

Indeed, the new images serve as a reminder that Pluto isn't the only game in town for New Horizons.

"Charon is now emerging as its own world," said GGI deputy team leader John Spencer, of SwRI. "Its personality is beginning to really reveal itself."

During the July 14 flyby, New Horizons will zoom past Pluto at a distance of 7,800 miles (12,500 km), capturing the first-ever close-up views of the dwarf planet and Charon.

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Mike Wall
Senior Space Writer

Michael Wall is a Senior Space Writer with and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.