Earth, Mars born from same cloud of gas and dust, yet formed differently: Study

Co-lead researcher Haiyang Wang, assistant professor at the Globe Institute, University of Copenhagen, said, “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.”

While both protoplanets and planetesimals serve as building blocks for planets, the two differ in sizes —planetesimals are solid, kilometre-sized building blocks formed from cosmic dust and protoplanets are larger, moon- to Mars-sized planetary embryos.

The study, published in the journal Nature Astronomy, investigates how Earth and Mars formed 4.5 billion years ago by analysing specific elements in the crust and mantle of the two planets.

Scientists broadly agree that planets are formed primarily in one of two ways, or through a hybrid of two processes. Planets either emerge when giant space rocks, known as planetesimals, collide, or when the large rocks accumulate smaller particles, a process known as pebble accretion.

Planetary scientists have not settled on which of the two processes or a combination thereof would best explain how rocky planets such as Earth and Mars formed.

The researchers said their findings support the hybrid model and that the study goes one step further, offering a more explicit explanation of how Earth and Mars formed 4.5 billion years ago. They focused particularly on volatile elements, which evaporate relatively easily at high temperatures, such as sodium, zinc and potassium.

According to the researchers, the presence or absence of volatile elements acts as a chemical fingerprint revealing the processes planets underwent during their formation.

Using computer models, they can then determine which formation scenarios are the most likely explanations for the origins of Earth and Mars.

“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,” Johansen said.