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May 19, 2011

In the middle of the 19th century, European astronomers were racing to discover new "planetoids" -- small bodies orbiting the Sun between the orbits of Mars and Jupiter. The race was run not just from observatories, but from back yards and apartment balconies in London, Paris, and many other cities.

On the night of May 19th, 1851, for example, John Russell Hind discovered one from a private observatory in London. It was the 14th planetoid discovered, and the fourth by Hind alone. He named it Irene, after a daughter of Zeus who was a Greek symbol of peace. The name honored London's Great Industrial Exhibition, which celebrated the peaceful pursuits of arts and sciences.

The first planetoid had been discovered 50 years earlier, and astronomers originally described it as a planet. Over the next few years, though, they found three more objects in similar orbits. They were much smaller than Venus, Mars, and the other major planets, so they were described as minor planets or "planetoids."

German astronomer Heinrich Olbers suggested they were the remains of a fractured planet. The idea picked up steam a few decades later, as many more planetoids were discovered.

Today, these objects are known as asteroids. More than a hundred thousand have been discovered in the same zone as the first ones, the asteroid belt. Instead of a fractured planet, though, they're probably the building blocks of a planet that never was -- kept apart by the gravity of nearby Jupiter.


Script by Damond Benningfield, Copyright 2011


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