Debris of Giant Impacts

During the end of terrestrial planet formation, growing planetary embryos collided with each other during a period known as the giant impact phase. This is a widely hypothesized phase; however, the details vary in several ways. Some theories suggest that the single Moon-forming impact was the only one to occur. Others propose a powerful perturbation brought about by the giant planets resulted in numerous collisions. Despite these disagreements, many conflicting scenarios can accurately reproduce the correct masses and orbits of the planets, but a consensus as to which is correct has yet to be determined.

One thing all scenarios have in common is that impact debris is produced. The ejected debris may fly into the Sun or another planet, be launched out of the Solar System entirely, or may find a home in dynamically stable regions of the Solar System, such as the asteroid belt. The theoretical values of total debris mass in the asteroid belt can be compared to observations from the asteroid belt. This comparison will give another indication of how accurate a scenario may be.

One formation scenario that reproduces many astrophysical constraints is the early giant planet instability model. This theory suggests that the giant planets underwent a period of orbital instability caused by the dispersal of the Sun’s gaseous disk. This instability would greatly perturb the planetary embryos and incite a relatively violent era of collisions. We will begin our search for the true terrestrial planet formation scenario by first looking at the early instability scenario. Unlike past work, we will simulate so-called imperfect accretion quantifying the amount of debris created and tracking it to its final location. From our simulations, we can compare the amount of debris that ends up in the asteroid belt to an observationally obtained upper mass limit. This limit sums the amount of mass in the asteroid belt that could have come from the forming planets. In doing this, we can assess how likely it is for this scenario to have occurred.

We expect to retrieve a few different possible results from this work. The most promising of results would be finding that the simulation produces a total debris mass in the asteroid belt that is close to the observed upper limit but does not exceed it. Our simulation may produce a total debris mass in the asteroid belt that greatly exceeds the limit. This result would support a conclusion that the scenario is not the one that formed the terrestrial planets. We may also find that the amount of debris is significantly less than the limit. This would warrant further investigation since a lower bound has not been determined.