So rather than continually harp on about Pluto and how is has annoyed me that they ‘demoted it’, I thought it might be advisable to focus on one of the god things that has come out of the IAU’s recent meeting. Ceres, the largest member of the asteroid belt, has been promoted to the status of dwarf planet.
Ceres satisfies the three defining factors of that category which are that is orbits the sun and isn’t a star, that its own gravity has forced it into a roughly spherical shape and that it hasn’t cleared the area around its orbit (i.e. there are lots of other bodies in the same region as Ceres: the other asteroids). Above is the best image that has been taken of Ceres. It comes from the Hubble Space Telescope.
Ceres accounts for one third of al the mass in the asteroid belt and orbits between Mars and Jupiter with a period of about 4.6 years. Ceres was discovered on January 1st 1801 by the Italian Giuseppe Piazzi by accident (he was looking for something else altogether). Its official name is 1 Ceres because it was the first object of its kind to be discovered, the next objects being the asteroids 2 Palla, 3 Juno and 4 Vesta. However only a month after its discovery, Ceres moved behind the Sun, from Earth’s perspective and the astronomers effectively lost it. Only three observations had been made and they were unable to predict where it would now be.
It took the mathematician Carl Friedrich Gauss several months to develop a method whereby an orbit could be determined from just three observations and on December 31st of 1801, exactly a year after its initial discovery, Ceres was rediscovered and located once again.
At that time no asteroid belt as we know it was even thought to exist and Ceres was thusly labeled a planet. But, as would be the case with Pluto 130 years later, Ceres just wasn’t enough like a planet for most people’s liking. It was too small and so William Herschel (the man who discovered Uranus amongst other things) coined the term asteroid, meaning star-like. It wasn’t long before more objects were discovered in the same region and 50 years later Ceres was no longer a planet but simple the largest member of the asteroid belt. It held that status until last week when it became a dwarf planet along with Pluto and 2003 UB313.
Ceres remains very much a mystery even today. The first mission to actually study it up close is NASA’s Dawn project and that will arrive at Ceres 2014 or 2015. It was a mysterious white spot on its surface, which no one has identified formally. In 1995 someone spotted a dark object, thought to be a crater, and named it Piazzi after Ceres’ discoverer but Piazzi was no longer detectable next time anyone looked!
I have included an image here from Wikipedia’s Ceres article showing the size of the first ten asteroids laid over our Moon. It shows very well how small Ceres really is at a diameter of 950 km. Ceres is now the closest Dwarf planet to the Earth at at time of writing was only twice as far from our us the Sun. However it is not generally visible to the naked eye. I welcome Ceres to the new club of dwarf planets and wish it well in future endeavours.
