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NASA's Pluto probe gets first look at Charon

Paul Sutherland, Feature writer
Jul 14, 2013, 7:00 UTC

Sen—NASA’s New Horizons mission has logged a key moment on its race to Pluto by catching its first glimpse of the former planet’s largest moon Charon.

The most powerful of its miniature cameras snapped a fuzzy image which nevertheless clearly shows the icy satellite as an object separate from the remote world that it orbits.

New Horizons was still 885 million km from Pluto, a distance that is greater than that of Jupiter from the Earth, when it took six images using its LOng Range Reconnaissance Imager (LORRI) on July 1 and 3.

Hal Weaver, New Horizons Project Scientist at the Johns Hopkins University Applied Physics Laboratory, in Maryland, said: “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! We’re very excited to see Pluto and Charon as separate objects for the first time from New Horizons.”

Charon, which was discovered in 1978, is the largest of five moons known to orbit Pluto. The fifth was only spotted last year in images taken in June and July 2012 by the Hubble Space Telescope.

New Horizons, the fastest probe ever fired into deep space, was launched in January 2006 and accelerated to Solar System escape velocity of 55,500 km per hour by a solid-fuelled engine. It is flying so fast that it was already passing Jupiter by February 2007.

Even so, it will not reach Pluto - which lost its planet status while the probe was already en route - until 2015 after a nine-year journey. When it gets there, it will not have time to hang around as it gathers data because its high speed will carry it on into the Kuiper Belt.

Pluto and Charon

Six images of Pluto taken from New Horizons were combined to produe this image which is shown plain and with the bodies circled. Credit: NASA/JHUAPL/SwRI

But as it approaches and zips past, New Horizons will study Pluto and its moons as much as it can using its cameras, a radio science experiment, ultraviolet and infrared spectrometers and space plasma experiments.

These will check out the global geology and geomorphology of Pluto and Charon, map their surface compositions and temperatures, and examine Pluto’s atmosphere in detail. The probe carries a large radio dish 2.1 metres in diameter to allow it to communicate with Earth from a distance of 7.5 billion km.

The discovery of such a relatively large number of moons around Pluto has led mission scientists to wonder what other rocky debris might litter its neighbourhood. Even a small object could pose a threat to New Horizons because of its incredible speed of 15.4 km per second.

New Horizons’ principal investigator Alan Stern, of the Southwest Research Institute, says that the team has a contingency plan, if the encounter looks too dangerous, in which they will send the probe at a greater distance than the 10,000 km currently planned for closest approach.

Of his probe’s first glimpse of Pluto with Charon, Stern said: “We’re excited to have our first pixel on Charon, 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!”