Earth and Mars may have formed through different mixtures of planetary building processes, despite developing side by side.
Earth and Mars formed near each other about 4.5 billion years ago, yet new research suggests they grew through very different processes.
“The most surprising result was that Earth and Mars appear to have formed in different ways. You might have expected that two planets formed side by side in the same solar system would share a more similar formation history,” says Professor Anders Johansen, who studies planet formation at the Globe Institute, University of Copenhagen. He co-led the new study with Assistant Professor Haiyang Wang.
Two Different Paths to Planet Formation
Rocky planets can grow through collisions between large bodies called planetesimals, through pebble accretion, in which smaller particles are swept up, or through a combination of both.
The new study supports that hybrid picture, but also indicates Earth and Mars relied on those processes in very different proportions.
“At least 75 percent 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 percent. In contrast, roughly three-quarters of Mars’ mass appears to come from planetesimals, with the remaining quarter originating from pebble accretion,” says Haiyang Wang.
Chemical Clues From the Early Solar System
To reconstruct the planets’ histories, the researchers analyzed volatile elements such as sodium, zinc, and potassium in their crusts and mantles. Because these elements can evaporate at high temperatures, their present-day abundances preserve clues about the conditions each planet experienced while forming.
The team combined those chemical fingerprints with computer models to test which formation scenarios best matched the planets seen today.
“It is a major detective job to figure out what happened back then when most of the evidence disappeared long ago. 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,” says Anders Johansen.
The models still depend on assumptions because the exact composition of the Solar System’s original building materials is unknown. Even so, the researchers say the contrast between Earth and Mars remained consistent when those assumptions were changed.
“The exact percentages may vary somewhat, but our analyses consistently indicate that Earth and Mars formed in two different ways. Our method provides a more precise and direct way of understanding planet formation than the more widely used isotope-based approach, which can often be interpreted in multiple ways,” says Haiyang Wang.
Implications for Habitable Worlds
The same approach could eventually help researchers study rocky planets beyond the Solar System. Formation conditions influence how much volatile material a planet retains, including water and other substances linked to habitability.
“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,” says Anders Johansen.
Reference: “Volatile depletion in rocky planets as a chemical fingerprint of hybrid accretion” by Haiyang S. Wang, Anders Johansen, Ziyan Xu, Marie-Luise Steinmeyer, Michiel Lambrechts, Elishevah van Kooten, Chao-Chin Yang, Zhaohuan Zhu, Dante S. Lauretta and Martin Bizzarro, 25 September 2026, Nature Astronomy.
DOI: 10.1038/s41550-026-02984-6
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3 Comments
I do not believe that Earth and Mars formed this way. Most of science has it wrong on or solar system. Let me break this down a little bit. Our solar system is the perfect example of perpetual motion. Our Sun is actually responsible for planet creation. The planets in our solar system rides through space on a conveyor belt. Every planet is slowly moving closer to the Sun. You can literally break the rock planets down like this, lets say Earth for example. Look at the layers of the planet, each layer represents where the planet used to be in the solar system. The planet core, used to be where Pluto is right now when it was just a core. As this core started being pulled inward, it started to interact with the Sun, heating up slightly. This slight heating along with the gradual pull started a rotation on the core. This rotation in turn starts pulling in silica dust and gasses from space as it travels through. As it pulls in more and more, it compounds and starts acting like a thermal blanket. Now we are at the next phase, Uranus. In this phase it starts building the outer core of the newly forming planet. About out of room, to be continued.
You can literally line up each layer of the planet to the position of the planets up to Mars, the first rock planet. In order to understand the position of each of the rock planets, you have to see the bigger picture and understand the end result. How does the Sun keep burning without exhausting it’s fuel source? Simply put, it doesn’t. The Sun creates its own fuel source in the shape of a giant compacted fuel pellet. This pellet being the planets. The Sun creates the planets just to eat them and refuel, also adding girth to the Sun each time. Think about it like this, if you throw a handful of saw dust into a blast furnace, it will turn to ash within a inch or two. If you take that same handful of saw dust and compact it into a pellet, then throw it into that same blast furnace, it will reach the center and keep burning for awhile. Same concept with our planets and Sun, just on a much larger scale.
You can literally line up each layer of the planet to the position of the planets up to Mars, the first rock planet. In order to understand the position of each of the rock planets, you have to see the bigger picture and understand the end result. How does the Sun keep burning without exhausting it’s fuel source? Simply put, it doesn’t. The Sun creates its own fuel source in the shape of a giant compacted fuel pellet. This pellet being the planets. The Sun creates the planets just to eat them and refuel, also adding girth to the Sun each time. Think about it like this, if you throw a handful of saw dust into a blast furnace, it will turn to ash within a inch or two. If you take that same handful of saw dust and compact it into a pellet, then throw it into that same blast furnace, it will reach the center and keep burning for awhile. Same concept with our planets and Sun, just on a much larger scale.