The asteroid belt could just as easily be the wreckage of the solar system. Asteroids, comets and other objects floating in it are mostly junk from eons ago.
So if so much garbage exists in the asteroid belt, then where is the impact debris from the violent collisions that occurred when the solar system was still in its wayward youth? There is nothing on file. This was the same question Arizona State University researchers Travis Gabirel and Harrison Allen-Sutter were asking when they decided to find out through computer simulations. It turns out that the debris really did disappear into the air.
“The final assembly of the planets involves mutual collisions of large protoplanets of similar size (‘giant impacts’), paving the way for modern geological and atmospheric processes,” they said in a study recently published in Letters from the Astrophysical Journal. “However, the thermodynamic consequences of [these] the impacts are… poorly understood.
Billions of years before Earth saw a dinosaur, the collisions that would have created the missing debris actually vaporized it before it ever had a chance to drift toward the asteroid belt. Forming planets means that the protoplanets have to crash into each other. Gas giants and other huge planets affected impact velocities, causing supersonic collisions between protoplanets that were at least the size of Mars, helpless in the face of monster gravity. Some of these protoplanets were destroyed and ended up in the asteroid belt.
It was the intense heat generated by these huge collisions that eventually turned the rock into vapor. This was more likely to happen on Martian-sized or larger planets (which might explain why smaller protoplanets from this era are still found in the asteroid belt) that experienced additional gravitational push from the gas giants or several immense impacts. Earth has also taken its share of hits. The gaseous debris easily left the solar system, taking with it evidence of the impacts, and the effects of solar radiation wiped out whatever was left.
Embryonic planets would form fairly quickly – 1 to 10 million years, that’s pretty fast in cosmic terms – from pebbles that have accumulated in larger and larger bodies. Impacts were something that was inevitable at the start of the solar system. When protoplanets got large enough, whether they were future rocky planets or gas giants, so did their gravity, which became the authors of gravitational disturbances. They continued to collide at higher speeds as they continued to grow. This means that the impact speed was proportional to their mass, but it gets worse.
Collisions between larger planets meant that the shock heating caused the released debris to escape faster than the speed of sound. Post-impact heating, or the heat generated by the impact itself depending on the speed and force with which one object crashed into another, made sure to vaporize the debris that was already collapsing at such high speeds. Wandering gas giants that were still figuring out their orbits would miss smaller objects and increase the rate at which their debris escaped, which is why accretion wasn’t quite as effective.
The evidence may not have been completely erased. There are pristine or near-pristine moons and asteroids that have remained intact and may still have traces of debris sprayed onto their surfaces. Another possibility is the Moon. Research may help us better understand how the Moon was formed, as it is believed to have originated as a result of a collision that released this debris. Still, things are missing.
“The ultimate fate of the debris in our simulations, however, is subject to processes that we do not solve (condensation, collisional grinding, chemistry, radiative transfer, etc.) and deserves further study,” the researchers said.
This breakthrough could further help us better understand star systems outside our own. Similar phenomena probably occurred among exoplanets, and there could be an Earth among them.