A team of scientists has highlighted a new potential mechanism for the delivery of water to Earth, offering a promising perspective compared to previous theories.
Based on numerous observations of the Solar System, as well as others made using the ALMA radio telescope of extrasolar debris disks, the study was published in the journal *Astronomy and Astrophysics* on December 3, 2024.
Water is an essential element for life on Earth; however, scientists believe that the early Earth was devoid of it at the time of its formation. Located too close to the Sun, our planet would have been too hot to retain water initially. Current theories therefore suggest an external supply of water occurring during the first 100 million years of Earth's history.
Until now, the prevailing theory posited that icy bodies, similar to comets, collided with Earth, thus bringing water. However, this scenario requires a cosmic "billiard game," where complex dynamic mechanisms send these icy objects toward Earth at a specific time and in sufficient quantities. Being somewhat random, this scenario has been questioned for its robustness and its universality across all extrasolar systems.
Based on precise isotopic measurements taken in Earth's atmosphere, as well as recent observations of asteroids (notably the results from space missions that approached asteroids like Hayabusa 2 and OSIRIS-REx), a new evolutionary model of the asteroid belt has been developed and tested against terrestrial data.
Additionally, observations of extrasolar disks, akin to our asteroid belt, were conducted using the ALMA radio telescope to test the universality of this new water delivery mechanism. It could potentially apply successfully to a variety of extrasolar systems.
The new study proposes an alternative, less random mechanism
If, as currently believed, asteroids formed as icy bodies within a cold primordial disk, then as this young disk dissipated, the asteroids, warming up, gradually released their ice as water vapor. This water vapor then formed a new disk, primarily composed of water, surrounding the asteroid belt and orbiting the Sun.
Step-by-step depiction of a new model for the distribution of water on the inner planets of the Solar System, including Earth. Five million years after the Sun's birth, asteroids in the main belt release water vapor under the influence of solar energy.
This vapor bath gradually diffuses into the inner Solar System, eventually enveloping the planets, which capture part of it, contributing to ocean formation between 10 and 100 million years later. © Sylvain Cnudde/Observatoire de Paris - PSL/LESIA
Through dynamic forces, this water vapor disk gradually expanded, eventually reaching the inner planets of the Solar System, including Earth. When these planets found themselves within this water vapor bath, they were able to capture part of it, thereby contributing to the formation of oceans.
This mechanism also helps explain the presence of water on other planets in the Solar System. With the potential to have universal applicability, it offers a promising route for identifying exoplanets capable of hosting water and, potentially, life.
References:
Quentin Kral et al, "
An impact-free mechanism to deliver water to terrestrial planets and exoplanets", *A&A*, December 3, 2024.