New Horizons Spies Charon

Pluto’s Largest Moon, Ahoy!

There be another moon, Captain!!

In a couple of years we’ll all be goggling over images from the New Horizons spacecraft as it whizzes through the Pluto system. Right now, the spacecraft is about 880 million kilometers from Pluto and closing in fast at a speed of 16.26 kilometers per second (relative to Earth). On July 1-3, the New Horizons Long Range Imager (LORRI) trained its eye on the distant dwarf planet to grab a snapshot of the system. The image it sent back showed Pluto quite clearly, and right next to it, the largest moon, Charon. The two worlds are about 19,000 kilometers away from each other, so at such a great distance, this is a pretty big milestone for the spacecraft’s imaging system.

Charon was officially discovered in 1978 by astronomer James Christy, who was using a 1.55-meter telescope at the U.S. Naval Observatory facility in Arizona. It’s a smallish world, measuring only about 1,200 kilometers across (about half the size of Pluto). The surface appears to be covered with water ice, and may be getting “refreshed” through the action of cryo-geysers venting material up from beneath the surface. That makes it an interesting world to explore in its own right, next to Pluto.

In case you haven’t been keeping up with the Pluto news (and really, who HASN’T been thinking about Pluto and its planetary status, eh?), New Horizons is a robotic mission set to explore Pluto and its five moons. It will sweep past at about 12,000 kilometers from Pluto’s surface and study the moons before heading out to explore other parts of the Kuiper Belt region of our solar system where Pluto and other dwarf planets orbit.  In October this year it will be just 5 astronomical units from Pluto.  (An astronomical unit is the distance between Earth and the Sun, 149.5 million kilometers). To give you some perspective on that distance, Jupiter and the Sun are just over 5 AU apart.

New Horizons was launched on its headlong rush out to the solar system deep-freeze on January 19, 2006. After it does its look-see at Pluto, Charon, Nix, Hydra, Kerberos and Styx, then the spacecraft will proceed to check out various frozen worlds called Kuiper Belt Objects before the expected end of its mission in 2026. If all goes well, and New Horizons continues to function, it will begin exploring the outer reaches of the heliosphere (the farthest reaches of the solar wind), in late 2038. Right now, the only spacecraft we’re getting data from in THAT part of the solar system are the Voyager 1 and 2 missions. So, stay tuned for more Pluto system news as it happens!