Researchers investigate origin of water on Earth

Results from a deep investigation led by a team of researchers have recently demonstrated that the water we are enjoying on the Earth has been there since its formation.

Water is no doubt one of the essentials to sustain life, and hence the question of the origin of water on Earth is primordial. A major challenge faced while investigating this question is that Earth has lost all the traces of its formation since it is an active planet.

A team of numerical modellers and geochemists led by Cedric Gillmann - Universite libre de Bruxelles, ULB, funded by the EoS project ET-HoME - has decided to look far beyond Earth -- up to Venus -- to investigate the origin of terrestrial water.

While Earth and Venus could be considered as twin sisters, their respective geological and climatic evolutions diverged dramatically in the past, leading to Venus' present-day 92 bar atmosphere heated by an infernal greenhouse up to 470°C, opposed to the mild conditions and only 1 bar pressure at the surface of Earth.

In comparison to Earth, Venus' volcanic activity and outgassing are reduced because it has no plate tectonics, but has a stagnant lid instead. The evolution of the atmosphere of Venus is much easier to understand and model over geological times. Also, because of their proximity, the Earth and Venus should have received the same type of material during their history.

All these aspects combine to make Venus a perfect place to study the primitive evolution of terrestrial planets.

Using numerical simulations of impacts of different types of asteroids containing various amounts of water, the team has discovered that water-rich asteroids colliding with Venus and releasing their water as vapour cannot explain the composition of Venus's atmosphere as we measure it today.

It means that the asteroidal material that came to Venus, and thus to Earth, after the giant impact must have been dry, therefore preventing the replenishment of the Earth in water.

Because water can obviously be found on our planet today, it means that the water we are now enjoying on Earth has been there since its formation, likely buried deep in the Earth so it could survive the giant impact.

This idea has very deep implications in terms of habitability of ancient Earth, Venus, and Mars, as it suggests that planets likely formed with their near-full budget in water, and slowly lost it with time.

Because Mars is much smaller, it likely lost all its water while life developed on Earth. For Venus, those results shine a complimentary light on recent work advocating that water oceans existed at the surface of the planet and help constrain the maximum amount of water that can be expected on Venus. They will also help prepare the next generation of space missions to Venus.