Vaca “pebbles” are thought to be supporting evidence of the idea that mesosiderites were formed when two different kinds of asteroids crashed into each other. For example, if an asteroid with a nickel-iron core were to collide with another asteroid made up of eucritic material, like Vesta, experts believe one would get “injected” into the other. A collision of this type could potentially result in fascinating pieces like Vaca “pebbles”, which are composed of material you’d expect to see on the surface of an asteroid mixed with molten material you’d expect to see in the core of a nickel-iron asteroid!
It has been presumed that analyzing these eucritic pebbles and Vaca could have made scientists reconsider the formation of mesosiderites. Mesosiderites and pallasites are grouped together, because it was originally thought they’d formed in the same way, but now it is believed that mesosiderites formed by asteroidal collisions rather than by cooling.