New Study Rekindles Contested Question: Earth and Mars Had Different Origins

hubie writes:

Surprising discovery suggests that Mars and Earth formed through different processes. The finding could help scientists understand whether planets in other galaxies are habitable:

Four and a half billion years ago, Earth and Mars were born in the rotating cloud of gas and dust that would eventually become our Solar System.

Yet exactly how the planets formed remains one of the most disputed questions in planetary science.

Now, researchers at the University of Copenhagen are adding new evidence to the debate. Using a novel approach, they have reconstructed the earliest stages of the planets' formation by analysing their chemical composition.

And the results surprised them.

"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.

Today, researchers broadly agree that planets are formed primarily in one of two ways, or through a hybrid of both processes:

Planets either emerge when giant space rocks, known as planetesimals, collide, or when these 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 behind the new study believe that their findings support the so-called hybrid model. However, the study takes one step further and offers a more explicit explanation of how Earth and Mars formed 4.5 billion years ago.

"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.
Planetary chemistry reveals the past

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