As our Solar System took shape about 4 billion years ago, it was likely a hotbed of formation with asteroids, comets, and ultimately planets coming into existence as they built up material.
Now, scientists have found evidence for at least one ancient mini-planet that also formed in the early Solar System, before being broken apart possibly by a violent collision. The findings are published in the Monthly Notices of the Royal Astronomical Society.
In the study, researchers led by Apostolos Christou and Galin Borisov at the Armagh Observatory and Planetarium in Northern Ireland, UK, looked at a number of Trojan asteroids that orbit in the same plane as Mars. Trojans are objects that follow or lead a planet in its orbit, staying in pockets of gravitational stability known as Lagrange points.
The most famous Trojan asteroids orbit Jupiter, which is thought to have about 6,000. But Mars has some too – nine have been found at the moment – and some may have the same origin. This suggests they came from the same body, before being split apart.
To reach this conclusion, the study authors used the Very Large Telescope (VLT) in Chile to examine the light coming off two, called (385250) 2001 DH47 and (311999) 2007 NS2. They compared this to another Mars Trojan, 5261 Eureka, which is about 2 kilometers (1.2 miles) across.
Seven Trojans are grouped up around Eureka at the L5 Lagrange point with the sole other Trojan orbiting on the other side of Mars in the orbital plane. This already hinted that they came from the same place.
Most of the Mars Trojans orbit at L5. Apostolos Christou
But it wasn’t until this study that we got a good look at what they’re made of. Studying the aforementioned Trojans, the researchers found that they had an extremely similar composition to Eureka. What’s more, they were also mostly composed of olivine, which is a mineral that normally forms under high pressure and temperature associated with a large body.
This points to the idea that these asteroids all came from a mini-planet, or a planetesimal, in the inner regions of the early Solar System. "The simplest explanation is that they originated from the same parent body," Christou told IFLScience.
Eventually, it’s thought that a collision likely destroyed this object, although the exact specifics of such an event aren’t clear. Christou noted that this likely happened before Mars had fully formed.
Nonetheless, it’s a cool find. And the authors note in their paper that these asteroids “might well be samples of the original building blocks that came together to form Mars and of the other terrestrial planets.” So it gives us a little glimpse into our past, too.