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Racing toward Pluto, spacecraft spies tiny moon Hydra

The New Horizons spacecraft – due to encounter Pluto in July 2015 – has spotted Pluto’s small, faint, outermost known moon, called Hydra.

Detection of tiny Pluto moon Hydra in July 2014 by New Horizons spacecraft.  Image via NASA / JHU / APL / SRI. New Horizons spacecraft.

Detection of tiny Pluto moon Hydra in July 2014 by New Horizons spacecraft. Image via NASA / JHU / APL / SRI. New Horizons spacecraft.

Pluto’s moon Hydra was detected twice by the New Horizons spacecraft LORRI (LOng Range Reconnaisance Imager) camera. The detections were made on July 18, 2014 and a few days later on July 20, from a distance of 430 million kilometers / 267 million miles. Analysis of those July images came in September 2014 by New Horizons Science Team members John Spencer of the Southwest Research Institute and Hal Weaver of Johns Hopkins.

New Horizons spied Hydra while conducting long exposures to try a method of detecting any possible smaller moons and rings – and possibly hazardous debris – when the spacecraft starts long-range encounter sequences in January 2015.

Forty ten-second exposures were made and the outermost known Pluto moon Hydra – only 160 kilometers / 100 miles wide – was detected.

Read more about New Horizons and the detection of Hydra

This 2005 image shows Pluto and four of its five known moons, as seen by the Hubble Space Telescope.  Image via HubbleSite

This 2005 image shows Pluto and four of its five known moons. Image via HubbleSite

Pluto and its large moon Charon appear as a

Both Pluto and Charon are vastly overexposed in these July 2014 images and appear to merge into a bright “blob.” The little moon Hydra is marked by crosshairs in the lower image. Image via NASA / JHU / APL / SRI. New Horizons spacecraft

Bottom line: The New Horizons spacecraft has spotted Pluto’s small, faint, outermost known moon, Hydra, in July 2014. The photos were analyzed, and Hydra seen, in September. Hydra is one of five known moons for Pluto. New Horizons will begin its long-range encounter sequences in January 2015 and will sweep past Pluto in July 2015,.

Andrew R. Brown

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