SCIENCE LAB SCENICS : CHARON'S JOURNEY

 

SOME 4.5 billion years ago - the dwarf planet Pluto was suddenly joined by a companion. For a very brief period - perhaps only hours - they danced as if arm in arm before gently separating, a grand do-si-do that resulted in Pluto and its quintet of moons orbiting the sun together today.

Astronomers have long wondered how Charon, the largest of those moons, came to orbit Pluto.

A paper in the journal. Nature Geoscience described a sequence of events that may resolve the question.

Charon is about 750 miles across, while Pluto is nearly 1,500 miles in diameter. That proportion in sizes suggest that a number of conventional scenarios explaining how moons form are unlikely, including theories that Charon formed from debris around Pluto or was captured by its gravitational pull.

Could Charon's existence instead be explained by the kind of collision that is believed to have formed Earth's moon?

The sizes of Pluto and Charon meant that it was difficult to workout they '' didn't just merge like two blobs of liquid,'' the most likely outcome of such an explosive scenario, said Erik Asphaug, a University of Arizona planetary scientist and co-author on the paper.

If Charon hit Pluto at a relatively sedate speed of about 2,000 miles [ 3,200 kilometers ] per hour, the two would have remained in contact for about 10 hours before gradually separating but remaining together.

This encounter was described as a ''kiss and capture.''

Pluto would then have been rotating once every three hours, so the two would have swung around three times while joined together.

The angular momentum of a spinning Pluto would have pushed Charon slowly away but, crucially, left it trapped in Pluto's orbit. [ Jonathan O'Callaghan ].