Research by CLEVER Planets investigators Damanveer Grewal and Rajdeep Dasgupta reveals that the prospects for life on a given planet depend not only on where the planet forms, but also how, linking Earth’s nitrogen budget to the rapid growth of moon- to Mars-sized bodies.
In a study published in Nature Geoscience, Grewal and Dasgupta show the competition between the time it takes for material to accrete into a protoplanet and the time the protoplanet takes to separate into its distinct layers — a metallic core, a shell of silicate mantle and an atmospheric envelope in a process called planetary differentiation — is critical in determining what volatile elements the rocky planet retains.
Conducting high-pressure, high-temperature experiments using nitrogen as a proxy for volatiles, the researchers captured protoplanetary differentiation in action. They found that most of the nitrogen escapes into the atmosphere of protoplanets during differentiation, and is subsequently lost to space as the protoplanet either cools down or collides with other protoplanets or cosmic bodies during the next stage of its growth.
This process depletes nitrogen in the atmosphere and mantle of rocky planets, but if the metallic core retains enough, it could still be a significant source of nitrogen during the formation of Earth-like planets.
Grewal and Dasgupta estimate that feedstock materials for Earth grew quickly to around moon- and Mars-sized planetary embryos within 1-2 million years of the beginning of the solar system, far sooner than the time it took for them to completely differentiate, allowing sufficient volatile retention to satisfy Earth’s current nitrogen budget.
The study follows earlier works, one showing how the impact by a moon-forming body could have given Earth much of its volatile content, and another suggesting that the planet gained more of its nitrogen from local sources in the solar system than once believed.
Dasgupta says: “We are making a big claim that will go beyond just the topic of the origin of volatile elements and nitrogen, and will impact a cross-section of the scientific community interested in planet formation and growth.”
Read more about the study in the official Rice University press release, or check out the full paper here.