Thursday, August 25, 2011

The 5 Strangest Facts About Pluto

Pluto is so far away from Earth that everything we know about it can be written down on a couple of 3 x 5 inch index cards. But Pluto will come into clearer focus in a few years' time, though, as NASA's New Horizons probe is due to make a close flyby of the dwarf planet in July 2015, marking the first time a spacecraft has ever visited the frigid, faraway world.

For now, though, here are the five strangest facts about Pluto, the former ninth planet in our solar system:

1. Pluto used to be giant

When Pluto was discovered (by American Clyde Tombaugh in 1930), it was initially believed to be larger than Mercury, and possibly bigger than Earth. Now astronomers know that it's about 1,455 miles (2,352 kilometers) across — less than 20 percent as big as our planet. And Pluto is just 0.2 percent as massive as Earth. [Photos of Pluto and Its Moons]

2. It doesn't fall in line

Pluto has an extremely elliptical orbit that's not in the same plane as the eight official planets' orbits. On average, the dwarf planet cruises around the sun at a distance of 3.65 billion miles (5.87 billion km), taking 248 years to complete one circuit.

It's strange orbit means that, for a few years at a time, Pluto's orbit overlaps with Neptune's. This brings Pluto closer to Earth than Neptune, the eighth planet from the sun. Don't worry, though, Pluto and Neptune won't collide. more