Earliest Inner Solar System Planetesimals Shaped the Inventory of Moderately Volatile Elements in Terrestrial Planets

Scientists have long been intrigued by the origins of Earth’s fundamental elements and the reasons why some are absent. A new study uncovers an unexpected development in the narrative of our planet’s creation.

A recent study, spearheaded by Assistant Professor Damanveer Grewal from Arizona State University’s School of Molecular Sciences and School of Earth and Space Exploration, along with collaborators from Caltech, Rice University, and MIT, contests conventional beliefs regarding why Earth and Mars lack moderately volatile elements (MVEs). Essential for planetary chemistry, elements like copper and zinc are often found alongside vital components for life, including water, carbon, and nitrogen. Knowing their sources offers crucial insights into how Earth achieved its habitability. Compared to primitive meteorites (chondrites), Earth and Mars show a significant deficiency in MVEs, prompting critical inquiries into the processes of planetary formation.

The research was published in Science Advances and adopts an innovative perspective by examining iron meteorites — the remnants of metallic cores from the solar system’s earliest building blocks — to gain new understandings.

“We discovered clear evidence that the first-generation planetesimals in the inner solar system possessed a surprising abundance of these elements,” Grewal stated. “This finding alters our perspective on how planets gathered their essential materials.”

Previously, it was thought that MVEs were either never fully formed in the early solar system or that they were lost during the differentiation of planetesimals. However, this research tells a different story: many of the initial planetesimals retained their MVEs, implying that the ancestors of Earth and Mars lost these elements later due to violent cosmic encounters that shaped their development.

Interestingly, the researchers found that many inner solar system planetesimals maintained chondrite-like levels of MVEs, indicating they collected and kept MVEs even after differentiation occurred. This implies that the precursors of Earth and Mars did not originally lack these elements; rather, their depletion happened over an extended timeline of collisional growth, rather than through incomplete condensation in the solar nebula or the differentiation of planetesimals.

“Our research reframes how we perceive the chemical evolution of planets,” Grewal clarified. “It indicates that the foundational materials for Earth and Mars were initially rich in essential life elements, but their depletion was a result of intense collisions during the planets’ development.”