By Lydia Amazouz Published on August 21, 2024
Collected at: https://dailygalaxy.com/2024/08/rocky-exoplanets-rich-water-molten-cores/
A groundbreaking new study has revealed that many rocky exoplanets, particularly larger ones known as “super-Earths,” may have massive reservoirs of water trapped deep within their molten cores.
This discovery is reshaping how scientists view the potential habitability of exoplanets and challenges previous assumptions about the nature of water-rich planets.
The research suggests that as much as 95% of a planet’s water could be confined to its interior, locked away inside its iron-rich core, and unavailable for life at the surface.
Water Trapped in the Core: A Hidden Reservoir
The study, led by Caroline Dorn, a professor of exoplanets at ETH Zurich, highlights that during a planet’s early formation, it is covered in a molten ocean of magma. As this magma cools, it forms a solid crust, while the denser materials, such as iron, sink to form the planet’s core.
According to Dorn, water, which is one of the materials present during a planet’s formation, becomes dissolved in the magma ocean. “Planets are much more water-abundant than previously assumed,” Dorn explained, indicating that early planets draw significant amounts of water into their interiors as the planet forms.
As the magma cools, the water binds to droplets of iron within the molten material. These iron droplets, behaving “like a raft,” are transported deeper into the planet’s core, taking the water with them. Dorn adds, “The iron droplets behave like a raft that is conveyed downwards by the water.” This process effectively traps the water within the planet’s core, rendering it inaccessible to the surface where life might exist. Instead of forming vast oceans, the water remains buried, bound to the planet’s iron core in a manner that could have profound implications for planetary habitability.
The Implications for Super-Earths
While this process is similar to what happened on Earth, the research focuses on larger rocky exoplanets known as super-Earths. These planets can have masses up to 10 times that of Earth, leading to extreme internal pressures and temperatures. Scientists had previously been unsure whether such large planets could retain water in the same way as smaller planets like Earth. However, the new study suggests that even these super-Earths can trap vast amounts of water in their cores.
“The larger the planet and the greater its mass, the more the water tends to go with the iron droplets and become integrated in the core,” said Dorn. According to the research, iron in the planet’s core can absorb up to 70 times more water than silicates, which are common in a planet’s crust.
However, under the extreme pressure found in the core, the water no longer takes the familiar form of H2O. Instead, it breaks down into its constituent elements, hydrogen and oxygen, which are stored deep within the planet, effectively preventing the water from ever reaching the surface again.
This means that although water may be abundant inside these planets, it is trapped and inaccessible to life that could potentially exist on or near the planet’s surface. These findings upend the previous assumptions about so-called “water worlds”—planets thought to have deep, global oceans. Instead of oceans, these planets may have most of their water hidden within their cores.
Rethinking Habitability: Water, Oceans, and Life
The discovery that much of the water on rocky exoplanets might be locked away in their cores has profound implications for the study of planetary habitability. Scientists have long assumed that planets with large amounts of water on their surfaces—often referred to as “ocean worlds”—were prime candidates for hosting life. However, this new research suggests that the presence of vast surface oceans might actually be rare, and planets previously thought to be water worlds might have much of their water hidden deep inside.
For life as we know it to thrive, a planet needs not only water but also land. Water on its own may not be enough, as nutrients necessary for life are often washed from the land into the oceans, supporting ecosystems. Furthermore, land plays a vital role in regulating a planet’s climate through processes like the carbon cycle. Planets with only water and no land might, therefore, struggle to maintain the conditions necessary for sustaining life.
“Although water is essential for life, a planet with only water on the surface might not be habitable,” Dorn noted. Planets that lack land might miss crucial components that allow life to thrive, such as nutrient runoff from land into oceans, which feeds marine ecosystems. Additionally, the presence of landmasses helps regulate planetary climates over long periods of time, which is necessary for maintaining stable conditions that support life.
Investigating Hycean Worlds and Water-Rich Planets
The study’s findings also raise questions about the nature of so-called Hycean worlds—a type of exoplanet that is thought to have a thick hydrogen atmosphere and potential surface oceans. These planets, named after the portmanteau of hydrogen and ocean, were previously considered prime candidates for hosting life due to their warm, ocean-covered surfaces.
However, Dorn’s research suggests that many of these worlds may also be hiding large amounts of water within their interiors, which could alter our understanding of their habitability.
As Dorn pointed out, “If we find water in a planet’s atmosphere, there is probably a great deal more in its interior.” This suggests that even if water is detected in the atmospheres of Hycean worlds, the majority of it might be trapped in the planet’s core, making it unavailable to support life on the surface.
One such exoplanet that is drawing particular interest is TOI-270d, a super-Earth orbiting a red dwarf star 73 light-years away. TOI-270d has been studied using the James Webb Space Telescope (JWST), revealing signs of methane, carbon dioxide, and water vapor in its atmosphere. Dorn, who was part of the team studying this planet, noted, “Evidence has been collected there of the actual existence of such interactions [of water] between the magma ocean in its interior and the atmosphere,” supporting the theory that water on these planets is being drawn into their cores.
A New Frontier in Exoplanet Exploration
The discovery that water could be locked deep within the cores of rocky exoplanets changes how scientists view the potential for life beyond Earth. Instead of vast, ocean-covered planets, many exoplanets may be much drier on the surface, with most of their water hidden far below.
This has significant implications for future studies of exoplanets and their atmospheres. Understanding how water behaves in the interiors of these planets could help scientists refine their search for potentially habitable worlds and guide future missions.
The research, published in the journal Nature Astronomy on August 20, 2024, is a significant breakthrough in the study of exoplanets and could reshape our approach to identifying which planets might harbor life. As technology improves and scientists continue to study the atmospheres and interiors of distant worlds, we may soon gain a clearer picture of the conditions that make a planet truly habitable.
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