A recent study published in Nature sheds light on the formation of water on exoplanets and its implications for the search for life beyond Earth. An international team of researchers has explored the mechanisms that enable exoplanets to generate liquid water, a critical factor for habitability.
The study involved high-pressure laboratory experiments using a diamond anvil cell, where scientists utilized lasers to examine interactions between atmospheric hydrogen and a magma ocean beneath exoplanet surfaces. The experiments simulated extreme conditions, reaching temperatures of 4000 K and pressures between 16 to 60 gigapascals, which are far beyond those found on Earth, where average surface conditions are approximately 288 K and 0.0001 GPa.
The findings indicate that a magma ocean rich in hydrogen, combined with reduced iron oxide, leads to significant water production. According to Laurence Tognetti, a Staff Scientist and Deputy for Research Advancement at the Carnegie Institution for Science, this research supports long-standing theories regarding planetary formation and evolution, demonstrating that substantial water generation is a natural outcome of these processes. Tognetti stated, “This work demonstrates that large quantities of water are created as a natural consequence of planet formation. It represents a major step forward in how we think about the search for distant worlds capable of hosting life.”
The study primarily focuses on sub-Neptune exoplanets, which have masses between Earth and Neptune, featuring rocky interiors similar to Earth and hydrogen-rich atmospheres akin to Neptune. Although this combination is not found in our solar system, astronomers have identified nearly 1,000 sub-Neptunes among over 6,000 confirmed exoplanets. Some of these exoplanets are classified as super-Earths if their mass and radius are closer to Earth than Neptune.
Notable examples of sub-Neptunes with hydrogen-dominated atmospheres and rocky interiors include exoplanets located approximately 124 light-years, 218 light-years, and 73 light-years from Earth. All of these orbit M-dwarf stars, which are smaller and cooler than our Sun, resulting in smaller habitable zones. However, M-dwarf stars have significantly longer lifespans than larger stars, with estimates reaching trillions of years compared to the Sun”s approximately 10 billion years.
This research underscores the possibility that planets differing from those in our solar system might still cultivate the necessary conditions for life, whether as we understand it or in forms yet to be discovered. It also suggests that water could be more abundant on exoplanets than previously assumed, particularly in relation to established models of planetary formation and evolution. Future studies will likely continue to unravel the complexities of water production on exoplanets, which remains a central question in astrobiology.
