We've Just Found Asteroids As Old As Our Solar System And Have No Idea Why They're Different

Astronomers have just discovered the oldest asteroid family ever known to man, and it’s likely even as old as our own solar system!

Researchers studying data on asteroids, including from the the WISE space telescope, have found an asteroid family (asteroids that originated from a common source) that’s over 4 billion years old.

Until now, astronomers hadn’t seen asteroid families in our system older than 3 billion years, a few shy of the 4.5 billion years of age our solar system is. According to Gizmodo, the team had to first eliminate asteroid families we already know about, and then look for a type of very old rock.
The team was focused on a handful of asteroids they couldn’t identify as part of any existing families, but had similar albedos (the proportion of light reflected off them). They realised these few were ‘dark’ asteroids, and their material composition and large size pointed to an origin around the time the solar system was born. At the time, huge collisions were a frequent occurrence, and the primitive materials contained in these asteroids seemed to suggest that.
The team’s findings have mixed results for astronomers. For one thing, it confirms a theory that the asteroid belt in our solar system used to be larger, with planets like Jupiter, Saturn, Uranus, and Neptune being closer to the Sun. On the other hand, why do these early asteroids look so different from ones formed later? There are still a lot of questions to be answered, but at least we’re started in the right direction.