Earth and Mars formed side by side from the same cloud of gas and dust some 4.5 billion years ago, yet chemical analyses of their mantles reveal the two neighboring rocky planets grew through fundamentally different proportions of cosmic building blocks, according to a study published on September 25, 2026, in Nature Astronomy.
Chemical Fingerprints in Volatile Elements
To uncover how the solar system’s rocky worlds came together, researchers from the Globe Institute at the University of Copenhagen and their international collaborators turned to volatile elements like sodium, zinc, and potassium found in the planets’ crusts and mantles. Because these specific substances evaporate readily under high temperatures, their presence or absence serves as a chemical record of the intense heat and violence each world experienced during its infancy.
The research was conducted by a scientific team including Haiyang Wang, Anders Johansen, Ziyan Xu, Marie-Luise Steinmeyer, Michiel Lambrechts, Elishevah van Kooten, Chao-Chin Yang, Zhaohuan Zhu, Dante S. Lauretta, and Martin Bizzarro.
It is a major detective job to figure out what happened back then when most of the evidence disappeared long ago,
said Anders Johansen, a professor of planetary sciences at the University of Copenhagen who co-led the study, in a statement released by the Globe Institute. But even after 4.5 billion years, the compositions of Earth’s and Mars’ mantles remain the same. You can think of them as an imprint of the formation process.
Protoplanet Accretion Versus Planetesimal Collisions
Scientists have long debated the exact mechanics that shaped the early solar system. Nebula theory holds that the sun was surrounded by a massive accretion disk of gas and dust that gave rise to planetary bodies through two main pathways: the gathering of smaller particles known as pebbles, or repeated collisions between kilometer-wide rocky bodies called planetesimals. The new research supports a hybrid model combining both processes, but demonstrates that Earth and Mars relied on them in strikingly different measures according to findings published in Nature Astronomy.
“At least 75 per cent of Earth’s mass appears to originate from two young planets, known as protoplanets, that grew large by accreting pebbles, while planetesimals contributed up to 25 per cent.”
Haiyang Wang, assistant professor at the Globe Institute, University of Copenhagen
In contrast, Mars followed a nearly reversed trajectory. Roughly three-quarters of the Red Planet’s mass appears to stem from colliding planetesimals, with the remaining quarter contributed through pebble accretion as detailed by the research team. The team notes that the exact chemical makeup of the raw material that became Earth and Mars is unknown, meaning the calculations depend on assumptions, though adjusting those assumptions did not change the main conclusion.
Implications for Exoplanet Habitability
Understanding how volatile elements are lost or retained during planetary accretion does more than clarify our own solar neighborhood.
If we understand how planets lose volatile elements during their formation, we can also become better at predicting how much water and other life-supporting substances they ultimately retain,
Johansen concluded in comments distributed by the Globe Institute.
