The long-term goal of project area B is to understand the genetic relationships among late-accreted materials and the main planetary building blocks, and to quantify the importance of the final stages of accretion for the volatile accretion history of the terrestrial planets. Results obtained during the first funding period demonstrate that this goal can be reached through a combination of isotopic and chemical analyses of meteoritic and planetary samples. The results, together with results from various other studies, also reveal, however, that core formation and presumably also degassing on planetary precursor bodies may have obscured the chemical and isotopic signatures of planetary building blocks. As a consequence, specific chemical or isotopic signatures may provide seemingly contradictory constraints on the provenance and composition of late-accreted materials. Understanding the nature and origin of late-accreted materials, therefore, requires a multifaceted approach that combines different chemical and isotopic observations in a mutually consistent way. A major focus of the second funding period will, therefore, be on obtaining a more holistic picture on how the compositions of planetary building blocks evolved in space and time, and to identify the processes that shaped these compositions. As such, the overarching goal of project area B will remain, but it will be extended towards a more process-oriented focus, including differentiation processes that may control moderately volatile element abundances in the terrestrial planets.
Major research objectives and questions
- What was the composition of Earth, Moon, and Mars before late accretion, and was it volatile rich or volatile poor? (subprojects B1, B3, B6, B7, B8)
- How does the late accretion history on Mars compare with Earth? (subprojects B3, B6)
- How did the provenance and composition of the planetesimal population in the terrestrial planet region and the asteroid belt change over time? (subprojects B3, B5, B6)
- Were volatile element depletions in (building materials of) terrestrial planets caused by planetary degassing or inherited from thermal processing in the solar nebula? (subprojects B1, B7, B8)