Since the first object in what is now commonly known as the ‘Asteroid Belt’ was observed in 1801, over 100,000 asteroids have been found in the same region. More than 90 per cent of these have been discovered in the last decade and there are suspected millions more too small to be of note. So what are they all doing there and why aren’t these bands of space rock more common?
When the dwarf planet Ceres was first spotted, quickly followed by the large asteroids Juno and Vesta, it was proposed that they were the remains of a larger planet that had succumbed to a catastrophic event such as a massive impact with another celestial body. The theory stuck for decades but today most scientists consider this origin of the Asteroid Belt an unlikely scenario. The energy required to shatter a progenitor planet even of this small size would have been enormous and, besides, the range of elements and chemicals present in the various asteroids suggest they originated from something other than a single body.
It’s generally accepted that the Asteroid Belt is a vestige of our early Solar System. Though we still don’t know exactly how our planetary system evolved, it’s believed that a collapsing nebula created the Sun and then each planet – both rocky and gaseous – developed out of accreting particles orbiting in discs similar to today’s Asteroid Belt. However, the millions of particles between Mars and Jupiter were unable to form a planet in this way because they were perturbed by the mighty influence of Jupiter’s gravity. So instead they have remained as a disc of orbiting material to this day.