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New Horizons captures early image of Hydra

NASA's New Horizon spacecraft has images Pluto's moon, Hydra. Photo Credit: NASA

Almost exactly a year before its scheduled Pluto flyby, the New Horizons spacecraft, using its Long Range Reconnaissance Imager, photographed Hydra, one of the planet’s four tiny moons. The mission team did not expect to detect the tiny moon until January 2015, at which point the spacecraft will be twice as close to the Pluto system as it was this past July.

Using processing tools that will search for even smaller moons, as well as rings during next year’s flyby, the New Horizons team took 48 ten-second images of the Pluto system this past July 18 and 20.

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The early detection of Hydra was unplanned. Team members were using LORRI to practice taking the long exposure images that will look for even smaller moons, rings, and debris that could pose a hazard to the spacecraft as it approaches Pluto next spring.

Upon analyzing the July images, taken 267 million miles (430 million km) from Pluto, mission team members John Spencer, of the Southwest Research Institute, and Hal Weaver, of the Johns Hopkins University Applied Physics Lab, recognized they had captured an image of Pluto’s most distant moon.

“Hydra popped right out of the data, though it’s still very faint – several times fainter than the faintest objects the New Horizons camera was designed to detect – and still very close to Pluto,” Spencer said.

New Horizons Principal Investigator Dr. Alan Stern said he is excited by the view of Hydra, which he described as “a bonus from this summer’s spacecraft activities.”

The images from each day that showed the best views of Hydra were combined, and the stars in the background were removed digitally to illustrate Hydra’s movement around Pluto over the two-day period. The resulting processed images show Hydra as a faint overlapping pair of bright and dark spots above Pluto. Red and green crosshairs show Hydra’s positions on both dates. Pluto itself is over-exposed, and looks like a white blob in the center of the picture. A dark streak on the right of the image is a camera effect resulting from overexposure.

Nix, Pluto’s next brightest small moon, cannot be seen at this distance because it is closer to Pluto and cannot be separated from the planet’s glare.

The surprise of being able to image faint Hydra from this distance is especially welcome because it shows that the LORRI camera is functioning well and that the techniques planned for detecting possible hazards on approach to Pluto are working just as well, Spencer said.

Hydra is believed to be around 100 miles (160 km) wide. It was discovered by the Hubble Space Telescope, along with Nix, in 2005.



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Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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