Where Did Earth’s Water Originate From?
The Solar Nebula: A New Source of Earth’s Water
For decades, scientists have believed that Earth’s water came from ice-filled comets and asteroids. However, new research suggests that the solar nebula, clouds of gas and dust that formed after the sun’s誕生, may have also played a role.
The chemical composition of water is simple: two parts hydrogen and one part oxygen. Hydrogen is abundant in the universe, so any source of hydrogen could have contributed to Earth’s water.
Hydrogen from the Solar Nebula
Hydrogen gas within the solar nebula was incorporated into planets during their formation. Most of this hydrogen remains trapped in Earth’s core, but some escaped and contributed to the building blocks of water molecules. This hydrogen has a lower ratio of deuterium, a heavy hydrogen isotope, to normal hydrogen than water from asteroids or comets.
Water-Logged Asteroids and Solar Nebula Interactions
Early in Earth’s history, water-logged asteroids crashed into each other, forming planetary embryos with an outer layer of magma. Hydrogen-heavy solar nebula gas encountered this magma, creating an atmosphere and sending dissolved hydrogen into the embryos’ interiors.
Isotopic Fractionation and Earth’s Water Distribution
Isotopic fractionation caused normal hydrogen to move deeper into the core, while deuterium isotopes remained in the mantle. As Earth merged with other celestial bodies, it gained enough water and mass to reach its final size.
The Importance of Solar Nebula Hydrogen
Asteroid impacts generated most of Earth’s water, but a small portion near the core appears to originate from the solar nebula. This finding suggests that even planets far from water-rich asteroids may have water.
Implications for Exoplanet Habitability
The team’s findings could help scientists better understand the habitability of other planets. They indicate that planets may have a “floor” of water regardless of their distance from water sources. This supports the idea of rapid planetary growth and the potential for life on other worlds.
Additional Insights
- Water found deep within Earth’s interior has a different ratio of heavy hydrogen isotopes and normal hydrogen, indicating a separate point of origin from asteroids and comets.
- The solar nebula gas contributed to the formation of one out of every 100 water molecules on Earth.
- Earth’s water is likely a combination of sources, including asteroids, comets, and the solar nebula.
- The presence of solar nebula hydrogen in Earth’s water has implications for understanding the habitability of other planets.
