Ancient asteroid family is as old as the solar system

Ceaseless celestial collisions make it hard to keep a family together, but scientists think they’ve found a clan that has managed to stay intact in the violent vacuum of space for four billion years.

A new study published in Science, points to evidence that a family of asteroids has existed as one clump before the planets settled on their current orbits. A family in this sense is an assembly of asteroids that have come from a common ‘parent’ origin: i.e., a larger asteroid that collided with another. Astronomers have dated asteroid families dating three billion years, but this ancient batch are likely to reach back to the early days of the Solar System.   

So how do you date a family of asteroids? How do you even know if asteroids are related in the first place? As Gizmodo notes, asteroid drift is dependent on size, and this results in an identifiable pattern that can be detected, measured and analysed to make calculations about how long a particular asteroid has been travelling.  

Partnering with NASA’s NEOWISE team, the researchers were able to analyse and cross-check a vast amount of information about asteroids, then use a process of elimination to find a handful (big hands) of rocks that formed around four billion years ago – all of which shared a similar complexion, and measure over 35km in diameter.

“These are the most ancient ones, the originals, or the planetesimals, as we called them,” CNRS astronomer Marco Delbo’, one of the authors of the paper, told Gizmodo. “These are even older than four billion years. They must be as old at the Solar System itself, which is 4.567 billion years old.”

The findings offer a glimpse into what the Solar System was like during its early stages of development. For example, the presence of “planetesimal” asteroids supports the theory that a large asteroid belt once existed close to the sun, which including some of the giant planets before they migrated outwards. It also raises questions about what conditions in that belt led to the collisions that formed asteroids, and how this connects to the Solar System as it exists now.

Regardless, four billion years is quite a long time for fragments of rock to drift in the cold silence of space, but it’s probably less stilted than some family reunions.

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