For decades, astronomers have pondered the origin of Earth’s water. Did icy comets and asteroids deliver it long after our planet formed? Or was the water already present within Earth itself when it coalesced from a swirling disk of dust and gas? While the delivery-by-ice theory held sway for years, new research suggests that planets may create their own water as they take shape — potentially making life-sustaining oceans far more common in the universe.
This groundbreaking discovery stems from a series of experiments designed to recreate the extreme conditions prevailing during a young planet’s fiery birth. Scientists focused on sub-Neptunes, a common type of exoplanet larger than Earth but smaller than Neptune. These worlds are thought to have rocky cores enveloped by thick atmospheres rich in hydrogen gas — an ideal recipe for testing water formation within a planetary embryo.
To simulate this process, researchers created miniature versions of these planets using a specialized device called a diamond anvil cell. Molten rock rich in iron was compressed to pressures nearly 600,000 times greater than Earth’s atmospheric pressure and heated to temperatures exceeding 7,200 degrees Fahrenheit (4,000 degrees Celsius). This intense environment mirrors the conditions within a molten young planet shrouded by a thick hydrogen-rich atmosphere.
Under these simulated planetary crucible conditions, hydrogen dissolved readily into the molten rock. Importantly, this hydrogen reacted with iron oxides present in the molten material, producing substantial quantities of water. Crucially, these experiments demonstrated that water could arise directly from the chemical interaction between a planet’s nascent interior and its surrounding hydrogen-rich atmosphere – without any external contributions from comets or asteroids.
This finding dramatically alters our understanding of how planets acquire water. It suggests that creating vast oceans might be an inevitable consequence of planetary formation itself, making water a far more widespread ingredient in planetary systems across the cosmos than previously envisioned. The implications are profound: if water is so readily formed during planet birth, it increases the likelihood that potentially habitable worlds exist throughout our galaxy, brimming with the essential ingredient for life as we know it.
