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Up to 95% of an exoplanet’s water could be trapped deep within its iron core forever, changing everything we know about water worlds and making them more habitable than we thought.
“Planets “It contains much more water than previously assumed,” he says, outer planets At ETH Zurich in Switzerland expression.
When Planets are born By accumulating debris and enduring collisions with other protoplanets, they become so hot that their entire surfaces are covered in an ocean of molten rock. This magma eventually cools, forming a silicate-rich mantle and solid crust above a deep core of molten iron that coalesces over time as heavier materials sink toward the planet’s center.
Water is among the materials that planets are built from, and in the early days of a planet, water is present and dissolved in the magma ocean. Previous research has shown that young planets with a similar structure Size and mass relative to Earth — and therefore with relatively moderate internal pressures and temperatures — they can draw dissolved water from the magma toward their cores. Indeed, one study found that: Soil includes at least dozens of times more water It occupies more space in its interior than on the surface in the form of oceans as we know them.
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“Most of the iron is initially present as droplets in the hot magma soup,” Dorn said. Water in the magma can combine with these iron droplets as they sink toward the core. “The iron droplets act like a raft carried down by the water.”
That’s fine for Earth-sized planets, but most of the rocky exoplanets discovered by astronomers are much larger than Earth. These are called super worlds These worlds could be up to 10 times the mass of our planet, but it is not yet clear whether such worlds, with more extreme interior conditions, could draw water from a magma ocean as on Earth.
Dorn, along with Princeton researchers Haiyang Luo and Jie Deng, used computer modeling to understand how water interacts with the molten magma surface of a young, hot rocky planet to answer this question, and found that even on super-Earths, most of a planet’s water can reach its interior.
“The larger the planet and the more massive it is, the more water tends to move with the iron droplets and integrate into the core,” Dorn said. “Under certain conditions, it can absorb 70 times more water than iron silicates. However, due to the enormous pressure in the core, water no longer takes the form of H20 molecules, but instead exists in hydrogen and oxygen.”
This water is so deep that it is trapped in the core forever, with no way to reach it, so it is of no use to life on or near a planet’s surface. However, it could aid habitability in other ways.
Using radial velocity Doppler measurements, measuring the mass and radius of exoplanets transitions—respectively—we can calculate the density of these worlds (by dividing the planet’s mass by its volume calculated from its radius). The density of some exoplanets means that a significant portion of their mass, perhaps a quarter, is water.
The assumption was that this water existed in the form of an ocean tens of kilometers deep on the surface, but if this new research is correct, then most of the water would actually be within the planet, and water worlds with deep global oceans may be rare. While water is essential for life, a planet with only water on its surface (and no land) may not be habitable. For example, nutrients that sustain life flow from the land to the sea, and this same flow process is a vital part of the carbon cycle that maintains planetary climates over long timescales.
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The so-called “HyceanDorn believes the “worlds,” derived from the words hydrogen and ocean, deserve further study to test the theory that water was brought into a planet’s interior. Hycean planets have a rich hydrogen atmosphere, but they are also thought to be capable of hosting deep oceans at habitable temperatures.
As a planet’s mantle cools and before oceans form, some of the water dissolved in the rock may degas and rise to the surface, where it is released into the atmosphere.
“So if we find water in the atmosphere of a planet, there’s probably a lot more in its interior,” Dorn said.
Specifically, exoplanets TOI-270dorbiting red dwarf Located 73 light-years from Earth and 4.78 times more massive than our planet, the star intrigued Dorn, who was part of a team studying its atmosphere. James Webb Space Telescope and methane, carbon dioxide, and water vapor were found.
“There is evidence out there that these kinds of interactions do indeed exist. [of water] “It’s between the magma ocean inside and the atmosphere,” Dorn said.
The ability for water to seep into a planet’s surface rather than pool at great depths means there is greater potential for more habitable planets with shallower oceans in the galaxy.
The research was published today (August 20) in the journal Nature Astronomy.