It is believed that in the early solar system, the terrestrial planets - Mercury, Venus, Earth and Mars - were formed from planetesimals, small young bodies. Young planets grew over time through collisions and mergers to become what they are today.
It is generally believed that material released from violent collisions escaped and revolved around the sun, bombarding growing planets and altering the composition of the asteroid belt. But there are no records of these debris in the asteroid belt, which remains a mystery that has baffled astronomers and astrophysicists for decades.
Two scientists at the University of Arizona's School of Earth and Space Exploration, former NewSpace researcher Travis Gabriel and doctoral student Harrison Allen-Sutter, became interested in this discrepancy and set about creating high-tech computer simulations of collisions with surprising results.
“Most researchers are focusing on the direct consequences of collisions, but the nature of the debris has not yet been studied,” said Allen-Sutter.
Simulations have shown that instead of generating rock debris, large planetary collisions turn rocks into gas. Unlike solid and molten debris, gas leaves the solar system more easily without leaving traces of destructive events.
Their work was published in the Astrophysical Journal Letters and offers a potential solution to a longstanding paradox called the Missing Mantle Problem.
“It has long been realized that numerous major collisions are needed to form Mercury, Venus, Earth, Moon and possibly Mars,” said Gabriel, the project's principal investigator. "But the huge amount of debris expected from this process is not observed in the asteroid belt, so there has always been a paradoxical situation."
Their results may also help to better understand how the Moon formed, which is believed to have been born from a collision that threw debris into the solar system.
“After being formed from debris tied to the Earth, the Moon would also be bombarded with ejected material that orbited the Sun during the first hundred million years of the Moon's existence,” Gabriel said. “If this debris were solid, it could jeopardize or greatly affect the early formation of the Moon, especially if the collision was violent. But if the material were in gaseous form, the debris would not affect the early moon at all.
Gabrielle and Allen-Sutter hope to continue this line of research to learn more not only about our planets, but also about the large number of planets observed outside the solar system.
“There is growing evidence that some observations with telescopes can directly display giant debris from impact objects around other stars,” Gabriel said. "Since we cannot go back in time to observe collisions in the solar system, these astrophysical observations of other worlds have become a natural laboratory for us to test and investigate our theory."