Ceres and other forgotten worlds

Most people know that our solar system has eight planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.  Controversy surrounds Pluto, from it’s discovery in 1930 until it’s relegation from the premier planet league to more lowly the status of dwarf planet in 2006 it was our ninth planet. Its new lowly status restores the planetary numbers back to what we had between the (mid nineteenth century) discovery of Neptune and Pluto.

So it is rather odd to see in the London Science museum a model solar system (an Orrery) built in 1813 for the British astronomer William Pearson, It has not, as you might expect, seven, but eleven planets. No he wasn’t guessing or predicting what would be discovered, he was representing the orthodox view of the solar system at the time. There amongst the familiar innermost seven planets between the orbits of Mars and Jupiter are four we’ve almost forgotten Ceres, Vesta, Pallas and Juno. These are real worlds, although like Pluto they would by the mid nineteenth century be relegated, and their relegation was more severe than that meted out to Pluto condemned to virtually non-league status as asteroids.

Yet these four worlds are no mere fragments of rock. Ceres is a spherical world nearly 600 miles across with a light atmosphere and probably a substantial quantity of water. With a good eye and a dark night you can even see it from Earth without a telescope. It has been ignored by space exploration and barely mentioned in text books on our solar system for century and a half. It’s sisters have fared no better, although they are rather more potato shaped than spherical and look a bit more like what you might expect an asteroid to look like nobody much talks about Vesta, Pallas and Juno either.

In fact there are many many more. Hygiea an ovoid world the size of Belgium, Eunomia a rock world the size of Wales, and bizarrely a binary asteroid Antiope that is made up of two equal sized parts orbiting around each other. There are over two hundred more asteroids known to measure more than 70 miles across. In total there is thought to be over a million asteroids forming the asteroid belt.