Pluto And Charon: 99.5% of The Way There

A guest post by Joseph Friedlander

The New Horizons Probe is rapidly approaching the Pluto/Charon system.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Notice that this is a double world system, orbiting an exposed barycenter.  

 The fainter one is Charon, the brighter more massive one Pluto.
 The two are tidally locked,  with a period of 6 days, 9 hours and 17.6 minutes.

 Those are not just little rocks, either.
(No actual menace to the North American Continent should be inferred from this picture 🙂 )

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Because of density differences Charon weighs only 12% of what Pluto does. Charon would appear 7 times the diameter of Earth’s Moon from Pluto’s sky.  Pluto’s system is thought to be  made of less than half rock with water and other ices mixed in, including the very useful nitrogen and carbon ices.
A link explaining the concept of  the barycenter.

Here is something most familiar in binary asteroids– a space station in the exposed barycenter would literally (and accurately) perceive that the system was revolving around it.  One imagines that self-centered people who like to think the world (or better yet multiple worlds)  revolves around them might be drawn to that particular duty station.

The Moon and Earth’s center of gravity is within the Earth.
 The Solar System’s center of gravity is within the sun.

But Pluto and Charon have that exposed barycenter between them. Besides the obvious to a teenage mind Death Star like applications for battlestations that could rake (up to half) the surface of both worlds, there are also theoretical space station applications.

For example, you could melt essentially unlimited amounts of raw material and it would stay put, ideally sorted by density, without need to maintain the orbit. All the mass in the Pluto system would be shepherding it for you.  It would be a fantastic place for a shipyard– glossing over the yet more fantastic difficulties of getting out there and colonizing the place.

 ( If you had engines that could withstand 5 million Kelvin nozzle temperature (yes, 5 million) you could routinely reach the place in 6 months.  Yet I do someday expect Pluto colonization because as Poul Anderson pointed out long ago, a heat sink is a valuable resource on a big enough scale)

I imagine an exposed barycenter in the asteroids at the Jovian-Solar L5 point

would have far more immediate engineering uses— it might be interesting to write an article on the uses of such an exposed barycenter someday.  You could build a space colony around an exposed asteroid (or moon) moved to the barycenter and domed over.  But we digress from the mission.


January 19, 2006 Launch
February 28, 2007 Jupiter flyby/gravity assist
July 14, 2015 Closest approach to Pluto 
7:49:57 a.m. EDT (11:49:57 UTC) on July 14, 2015

July 15, 2015 First post-flyby data returned (P+1) Departure Phase 1 begins
Details at

Note that this July marks 50 years of detailed space probe results from the planets that include pictures. Before the summer of 1965, it was possible to fantasize about civilizations on Mars, lost cities on less survivable planets, and so on.
50 years ago that changed forever. Craters everywhere, and a solar system empty and awaiting Man’s colonization.  (NASA image).

Details at

General details of Pluto’s system