Mar 3, 2020 - Science

The Earth's gentle start

Illustration of gentle hands holding Earth
Illustration: Aïda Amer/Axios

The early Earth and other rocky planets may have formed quickly and gently, not violently through collapse and collision, as previously thought.

Why it matters: The details of Earth's formation are a long-standing mystery tied to how life may have arisen.

  • Specifics about planet formation are also key as scientists look out to other solar systems with worlds that might be habitable.

What's happening: A study published in Science Advances last week suggests that the proto-Earth may have hosted water before the Moon-forming impact occurred.

  • Other studies from NASA's New Horizons team found that Arrokoth — a world 1 billion miles past Pluto — also seems to have formed gently over time instead of quickly through collisions.

The big picture: Scientists think they have a pretty good understanding of how the giant planets like Jupiter and Saturn formed, but these new studies and years of research before them are forcing scientists to re-examine how rocky worlds like Earth, Mars and Mercury grew.

  • The gas giants likely formed by gobbling up pebbles, quickly becoming the dominant forces in their parts of the solar system.
  • Scientists are now trying to suss out the role this kind of growth may have played in the way that Earth and other small inner solar system worlds grew.

The intrigue: If Earth and other rocky worlds did grow through pebble accretion, it might have implications for when our planet was habitable.

  • "In principle, if we didn't have the Moon-forming impact, life could have formed much earlier on the Earth, probably," Martin Schiller, co-author of the Science Advances study, told Axios.

What's next: Scientists creating models of planetary formation are focusing on building our solar system from the ground up to test the various theories around how the inner planets — Mercury, Venus, Earth and Mars — formed.

  • Even if these rocky planets grew by pebble accretion, it's possible that dozens of protoplanets and asteroids that grew from that process collided in a violent cascade much in the same way that classical models show.
  • However, it's also possible that pebble accretion would have left the early inner solar system with just five objects — early Mercury, Venus, Earth, the Moon and Mars — with only one huge collision between the early Moon and Earth in the early solar system.
  • "It's really fun because we're reinvestigating all of the things that we had taken for granted and modeled in the past," planetary scientist Kevin Walsh told Axios.

Go deeper: A fingerprint of Earth from space

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