Tokyo: Materials that formed the Earth may have been formed very far out in the early solar system and then been brought in during the turbulent early history of the solar system, suggests a study.
Earth is believed to have formed partly from carbonaceous meteorites, which are thought to come from outer main-belt asteroids.
The new study led by researchers at Tokyo Institute of Technology suggests these asteroidal materials may have formed very far out in the early solar system and then been transported into the inner solar system by chaotic mixing processes.
The findings, published in the journal AGU Advances, suggest that the surface minerals present on outer main-belt asteroids, especially ammonia (NH3)-bearing clays, form from starting materials containing NH3 and carbon dioxide (CO2) ice that are stable only at very low temperature, and under water-rich conditions.
Based on these results, the study proposes that outer main-belt asteroids formed in distant orbits and differentiated to form different minerals in water-rich mantles and rock-dominated cores.
To understand the source of the discrepancies in the measured spectra of carbonaceous meteorites and asteroids, using computer simulations, the team modelled the chemical evolution of several plausible primitive mixtures designed to simulate primitive asteroidal materials. They then used these computer models to produce simulated reflectance spectra for comparison to the telescopically obtained ones.
Their models indicated that in order to match the asteroid spectra, the starting material had to contain a significant amount of water and ammonia, a relatively low abundance of carbon dioxide (CO2), and react at temperatures below 70 degrees Celsius, suggesting the asteroids formed much further out than their present locations in the early solar system.
If true, this study suggests that Earth’s formation and unique properties result from peculiar aspects of the solar system’s formation.
“Whether our solar system’s formation is a typical outcome remains to be determined, but numerous measurements suggest we may be able to place our cosmic history in context soon,” said lead author Hiroyuki Kurokawa from the Institute’s Earth-Life Science Institute (ELSI).
There will be several opportunities to test this model, for example, this study provides predictions for what the analysis of Hayabusa 2 returned samples will find. Hayabusa is the Japanese state space agency JAXA’s asteroid sample-return mission.
This distant origin of asteroids, if correct, predicts that there will be ammoniated salts and minerals in Hayabusa 2’s returned samples. A further check on this model will be provided by the analyses of returned materials from NASA’s OSIRIS-Rex mission.
