Dwarf Planet Ahoy! Spacecraft Spies Pluto and Charon


As NASA’s New Horizons probe powers through interplanetary space, it’s keeping a careful eye forward watching its target gradually loom larger on the proverbial celestial horizon. But earlier this month the spacecraft spotted something right next to Pluto — a pixelated Charon, the dwarf planet’s largest moon.

“The image itself might not look very impressive to the untrained eye, but compared to the discovery images of Charon from Earth, these ‘discovery’ images from New Horizons look great!” said New Horizons Project Scientist Hal Weaver, of the Johns Hopkins University Applied Physics Laboratory, Laurel, MD. “We’re very excited to see Pluto and Charon as separate objects for the first time from New Horizons.”

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New Horizons is still 550 million miles from Pluto, a little over two years from its historic flyby (scheduled for July 14, 2015), but through the mission’s highest-resolution camera, the LOng Range Reconnaissance Imager (LORRI), two distinct objects could be resolved.

Charon, which orbits Pluto at a distance of 12,000 miles (19,000 kilometers), was the first Plutonian moon to be discovered in 1978. There are known to be 5 natural satellites orbiting Pluto: Charon, Nix, Hydra, and two newly-named additions, Styx and Kerberos. During flyby, New Horizons will come within 7,750 miles (12,500 kilometers) of Pluto’s surface.

“In addition to being a nice technical achievement, these new LORRI images of Charon and Pluto should provide some interesting science too,” said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute. It is hoped that through these types of early observations of the Pluto system information about Pluto and Charon’s surface composition may be revealed.

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“We’re excited to have our first pixel on Charon,” added Stern, “but two years from now, near closest approach, we’ll have almost a million pixels on Charon — and I expect we’ll be about a million times happier too!”

This is indeed a superb technical achievement — New Horizons is proving itself to be a perfectly-engineered outer solar system emissary, providing us with a spaceship-eye view of the looming Kuiper Belt the little spacecraft will soon be exploring. Also, these long-range reconnaissance observations will soon outclass the best observatories on, and orbiting, Earth. This attribute may be of critical importance should Pluto be surrounded by more sub-resolution moons or dangerous debris clouds.

Image: New Horizons LOng Range Reconnaissance Imager (LORRI) composite image showing the detection of Pluto’s largest moon, Charon, cleanly separated from Pluto itself. The frame on the left is an average of six different LORRI images, each taken with an exposure time of 0.1 second. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

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