A group of scientists from the Paris Observatory has proposed a new theory about how water arrived on Earth, a key question for understanding the emergence of life on our planet. The study, published in the journal Astronomy and Astrophysics, suggests an innovative mechanism that could change our view of Earth’s past and that of other worlds.

Although today the oceans cover more than 70% of Earth’s surface, researchers believe that the newly formed Earth was a dry and hot place, incapable of retaining water due to its proximity to the Sun. This means that water had to arrive later, from space.

The traditional theory holds that water arrived via comets or icy asteroids that collided with Earth during the first 100 million years of its history. However, this scenario depends on extremely random cosmic events, like a celestial “game of billiards,” where these icy objects had to be deflected toward Earth in sufficient quantities.

Earth water solar system
Step-by-step demonstration of a new model for water distribution on the inner planets of the Solar System, including Earth. Five million years after the birth of the Sun, the asteroids of the main belt release water vapour under the effect of solar energy. This vapour bath gradually diffused into the inner Solar System, eventually enveloping the planets, which captured some of it to form oceans between 10 and 100 million years later. Credit: Sylvain Cnudde / Observatoire de Paris – PSL/LESIA

The new study proposes a different idea, based on recent observations of asteroids and debris disks in distant stellar systems, captured by the ALMA radio telescope. According to the scientists, when the Solar System was young, asteroids formed in a cold, ice-covered region. As the primordial gas and dust disk surrounding the Sun dissipated, the asteroids began to warm up, slowly releasing their ice as water vapor.

This vapor formed a disk around the Sun, composed mainly of water. Over time, the gravitational and dynamic forces of the Solar System caused this disk to expand, reaching the orbits of the inner planets, including Earth. In this process, our planet captured part of that vapor, which eventually condensed and contributed to the formation of the oceans.

The most exciting aspect of this theory is that it not only explains the origin of water on Earth but also on other planets in the Solar System. Furthermore, it suggests that this process could be repeated in distant stellar systems, opening new possibilities for identifying exoplanets with water and, potentially, life.

According to the researchers, this discovery could be of universal significance and offers a promising pathway to identify exoplanets capable of harboring water and, potentially, life.

SOURCES

CNRS

Quentin Kral, Paul Huet, et al., An impact-free mechanism to deliver water to terrestrial planets and exoplanets. A&A, 692 (2024) A70. DOI:doi.org/10.1051/0004-6361/202451263

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