Production: Jesús Nicolás
The Earth has been described as ‘that pale blue point of light’, due to the appearance of the abundant water on its surface. But water on the surface of the Earth is an unusual feature in the rest of the rocky planets studied. Due to the importance of water to sustain life, the question of the origin of water on Earth is paramount. A great challenge in investigating this question is that the Earth has lost all traces of its formation, as it is an active planet.
On the origin of water on Earth, some scientists believe that our planet lacked water before the catastrophic event that caused the Moon: just over four billion years ago, a planet similar in size to Mars would have just collided with Earth born, combining its materials and whose remains shaped the natural satellite of our planet. This impact would have hopelessly evaporated the Earth’s water.
For this reason, it is often believed that water reached Earth aboard asteroids , a product of the remnants of the formation of the solar system. Presumably, these droplets were falling on the Earth in an incessant bombardment that lasted 20 million years until they formed the oceans.
A team of numerical and geochemical modelers led by Cédric Gillmann, from the Free University of Brussels, ULB, has decided to look far beyond Earth, to Venus, to investigate the origin of terrestrial water. This team has discovered, thanks to a simulation, that water-rich asteroids that collide with Venus and release their water in the form of vapor cannot explain the composition of Venus’s atmosphere as we measure it today. So the other possibility is that water has been a part of the Earth since its inception and has remained hidden below the surface for millions of years. That would explain why the catastrophic events and hellish weather of an early Earth did not evaporate it.
Furthermore, this hypothesis implies that the planets likely formed on a ‘water budget’ including Mars and Venus. Since Mars is much smaller, it probably lost all of its water as life developed on Earth. For Venus, those results shed complementary light on recent work arguing that oceans of water existed on the planet’s surface and help limit the maximum amount of water that can be expected to be found on Venus. They will also help prepare for the next generation of space missions to Venus.
