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Pluto and moon Charon not cut from the same cloth

New Horizons The pictures coming back from NASA's Pluto-bound New Horizons spacecraft are still fuzzy, but they reveal a startling fact about the unexplored icy world: it has a different colour than its co-orbiting partner, Charon.

Images from New Horizons, currently within 24 million kilometres of its target, show Pluto is an orangey beige colour and Charon is grey

"The scientists are mulling over that one," says Lisa Hardaway, a manager with New Horizons camera-builder Ball Aerospace.

"They were expecting the two objects to be of the same material, but they're obviously not."

Even before the difference in colour was known, some scientists theorised that Charon coalesced from debris jettisoned into space after an object smashed into Pluto. A similar event is believed to be responsible for forming Earth's moon.

Charon, which was discovered in 1978, is nearly half the size of Pluto and it has enough mass to be a co-orbiting partner, the only known binary pair in the solar system.

Like Earth's moon, one side of Charon permanently faces its parent body, a configuration known as tidal locking. But Charon never rises or sets in Pluto's skies, appearing pinned over the same patch of real estate.

Like the gas giant Uranus, Pluto and Charon rotate the sun tipped on their sides, possible evidence of a massive impact.

Among the mysteries New Horizons should be able to solve is whether any of Pluto's atmosphere is winding up at Charon.

Computer models dating back to the late 1980s show that particles escaping from Pluto's atmosphere have to pass Charon's orbit, says New Horizons lead researcher Alan Stern, with the Southwest Research Institute.

"Charon's gravity can pull some of that atmospheric gas into orbit around itself or even onto the surface of Charon and create a secondary atmosphere," Stern says. "We're on the lookout for that.

"This would be fantastic if we discovered something like this," he adds. "Never in the history of planetary exploration have we seen two bodies with a shared atmosphere like we may see at the Pluto system. It could be quite a wonderland."

Images released on Monday show a distinct, and unexplained, dark region on Charon's north pole.

Both bodies have distinct dark and light patches on their surfaces, evidence of diverse landscapes. A bright fringe on Pluto, for example, may be a region where frost has formed from a polar cap that is evaporating during what is now Pluto's summer, says New Horizons scientist and imaging lead Jeff Moore, with NASA's Ames Research Center.

This week, New Horizon scientists will get their first look at Pluto and Charon in infrared light.

The spacecraft, which has been flying through the solar system for more than nine years, is slated to make a close pass by Pluto and its entourage of moons on July 14.

This article originally appeared on DiscoveryNews.com