A groundbreaking discovery by an Israeli-American research team challenges our understanding of how water forms on distant planets. The study reveals that many sub-Neptune planets, which are among the most common in our galaxy, may possess substantial amounts of water internally, rather than acquiring it from icy material formed far from their stars. This finding contradicts long-held assumptions about the formation of water-rich planets.
The research, led by Prof. Dan Shim of Arizona State University and Prof. Alona Vazan of the Open University of Israel, utilized advanced techniques to recreate the extreme conditions inside sub-Neptune planets. By employing a diamond anvil cell and pulsed laser heating, they were able to simulate the high-pressure and high-temperature environment at the boundary between the rocky interior and the hydrogen-rich atmosphere of these planets. Under these conditions, dense hydrogen reacts with molten rock, resulting in the formation of water.
The team's findings, published in the prestigious journal Nature, indicate that hydrogen-magma reactions alone can produce water in quantities reaching tens of weight percent, far exceeding previous estimates. This discovery challenges the notion that water-rich planets must have formed beyond the 'snow line,' where temperatures are low enough for water ice to condense. Instead, it suggests that hydrogen-rich sub-Neptunes can naturally evolve into water-rich planets, eliminating the need for large-scale migration to explain the presence of water-rich sub-Neptunes orbiting close to their stars.
Furthermore, the study reveals that even sub-Neptunes formed from dry materials can contain significant amounts of water. If these planets lose a portion of their hydrogen atmospheres due to stellar radiation, they could transform into super-Earths with substantial interior water. This water may eventually reach the surface or atmosphere as the planet's interior cools.
Prof. Shim and Prof. Vazan emphasize that this research reshapes our expectations about which planets can become water-rich. It also challenges the long-assumed link between a planet's orbital position and its water content. The study concludes that detecting large amounts of water in an exoplanet's atmosphere should not be taken as definitive evidence of its formation distance from its star, opening up new avenues for exploration and understanding of these fascinating celestial bodies.
