Of course, like the biggest mountain, the size of asteroids and the limitation of current observational technology mean that the biggest asteroids we know of are restricted to those in our own Solar System. There’s also a technicality in their definition: with a diameter of 950 kilometres (590 miles) and containing around one third of the total mass of the asteroid belt, Ceres used to be the biggest asteroid but was upgraded to ‘dwarf planet’ in 2006, handing fellow asteroid belt object Pallas the accolade of biggest known asteroid by default.
However, with an average diameter of 544 kilometres (338 miles) it’s still a whopper. Its closest contender for the top spot is Vesta, which has less volume but greater mass than Pallas. Between them, they make up around 16 per cent of the total mass of the asteroid belt and along with several other big asteroids, they were once believed to be part of a much larger ‘missing’ planet that was thought to orbit the space between Mars and Jupiter before being destroyed. That theory has since been debunked and it’s now known that Ceres, Pallas and their companions, along with the rest of the asteroid belt are the vestiges of a protoplanetary disc that was perturbed by the gravity of Jupiter and failed to accrete into a planet.
Pallas would easily fill the Vredefort crater in South Africa, the largest impact crater on Earth (at around 300 kilometres/186 miles in diameter), and is more than 30 times bigger than the meteorite that created the Sudbury Basin in Canada over 1.8 billion years ago. It’s 100 times bigger than asteroid 1998 QE2 that flew by Earth in March 2013, which could have caused wide devastation if it had impacted.