New Experiments Reveal How Planets Naturally Make Water During Their Formation

A groundbreaking study published in Nature has shown that water can form naturally during the birth of planets—no comets, asteroids, or external delivery needed. This research, led by Francesca Miozzi and Anat Shahar from the Carnegie Institution for Science, along with scientists from IPGP (Institut de Physique du Globe de Paris) and UCLA, provides the first experimental evidence that the process of planet formation itself produces large quantities of water.

How Planets Make Their Own Water

To understand how planets “get wet,” the team recreated the intense conditions of early planetary formation in the lab. Using a laser-heated diamond anvil cell, they compressed planetary analog materials to nearly 600,000 times Earth’s atmospheric pressure (about 60 gigapascals) and heated them to over 4,000 degrees Celsius (7,200°F). These extreme conditions are similar to what would exist inside a young, molten planet surrounded by a thick hydrogen-rich atmosphere.

The researchers found that hydrogen gas (H₂)—common in the atmospheres of newborn planets—reacts with iron oxide (FeO) in molten silicate (the building material of magma oceans). This reaction not only creates water (H₂O) but also causes hydrogen to dissolve deeply into the magma. Essentially, planets can make their own water as their fiery surfaces interact with their early atmospheres.

Why This Is a Big Deal

Until now, most theories about planetary water suggested it came from external sources—mainly comets or asteroids rich in ice that bombarded planets after they formed. But these new results suggest that water generation is a built-in feature of planet formation, not a lucky cosmic accident.

The experiments confirm two critical processes that happen during a young planet’s development:

1. Hydrogen dissolves into the molten rock (magma ocean), storing huge amounts of it within the planet.
2. Water forms directly when hydrogen reacts with iron oxide in that molten material.

This means planets can hold massive hydrogen reserves in their interiors while forming water at the same time. Both processes have major implications for how a planet’s core, mantle, and atmosphere evolve—and for whether that planet might eventually support life.

Sub-Neptunes and the Search for Habitable Worlds

Of the more than 6,000 known exoplanets, a type called sub-Neptunes is the most common in our galaxy. These worlds are larger than Earth but smaller than Neptune and are believed to have rocky interiors with thick hydrogen atmospheres. Because their early conditions are similar to what Miozzi and Shahar simulated, it’s likely that many of these planets naturally produce water through the same mechanism.

That discovery expands the definition of what might make a planet habitable. Worlds once thought too dry or too hydrogen-heavy could actually be rich in water. In other words, our galaxy could be teeming with planets that have oceans—or at least enough water to influence their surface and atmosphere chemistry.

Simulating Planet Birth in the Lab

The team’s setup involved creating miniature versions of young planets by compressing and heating materials representing magma oceans and primitive hydrogen atmospheres. These experiments produced measurable amounts of water and showed how hydrogen interacts with iron and silicon under extreme conditions.

The high-pressure environment, similar to what occurs deep inside a forming planet, allowed scientists to observe how molecular hydrogen acts as both a reactant and a heat trap. Hydrogen envelopes can behave like a thermal blanket, keeping magma oceans hot for millions (or even billions) of years—long enough for water production to occur on a massive scale.

Why Hydrogen Is So Important

Hydrogen is the universe’s most abundant element, and it plays a vital role in determining a planet’s chemistry. When a young planet is surrounded by a thick hydrogen atmosphere, it can influence everything from core formation to surface temperature.

In this experiment, hydrogen did more than just dissolve—it actively transformed iron oxides into metallic iron and released water. This is crucial because it helps explain why terrestrial planets like Earth have both metallic cores and volatile-rich mantles.

The researchers also discovered that the temperature of the magma was more important than pressure in determining how much hydrogen dissolved into the melt. This finding may help explain why planets closer to their stars, where surface temperatures are higher, could still retain significant amounts of hydrogen and water deep within.

Changing Our Understanding of Planetary Water

For decades, scientists have debated where Earth’s water came from. The leading theory was that asteroidal or cometary impacts delivered it after the planet cooled. But this new experimental evidence shows that water could have originated internally, from reactions between molten rock and hydrogen in the early atmosphere.

This also provides a missing piece of the puzzle for why so many planets in the galaxy might have water, even those that didn’t experience heavy bombardment from icy bodies.

If water formation happens naturally during the earliest stages of planet building, then it’s not unique to Earth—it’s universal. The conditions that produce water are the same ones that govern the formation of most rocky planets.

What This Means for Habitability

Water is one of the key ingredients for life as we know it. Understanding how it forms helps scientists determine which planets could be habitable. This discovery implies that liquid water might exist on far more planets than we ever thought possible.

Even if a planet loses its early hydrogen atmosphere later on, the water it formed could stay locked within the mantle or get released later through volcanic activity. This could lead to surface oceans or water vapor-rich atmospheres—both critical for life-supporting environments.

Limitations and Next Steps

While the findings are groundbreaking, there are still open questions. For example:

• How much of the generated water actually makes it to the surface?
• What happens when the hydrogen atmosphere is stripped away by stellar radiation?
• How do these chemical processes differ for planets of different sizes and compositions?

Researchers plan to combine experimental results like these with computer simulations to model how much water different types of planets can create and retain. Observations from telescopes like JWST (James Webb Space Telescope) may soon provide data to confirm whether such water-rich worlds truly exist.

A Broader View: What This Means for Earth

This research also invites us to reconsider Earth’s early history. It’s possible that part of our planet’s water didn’t come from space at all—it could have been born right here, from the same reactions between hydrogen and molten rock that the Carnegie team replicated in the lab. That idea connects our planet’s watery surface directly to its fiery origins.

If true, it means that planetary water formation is a universal chemical process—a natural byproduct of making planets themselves. That’s a profound shift in how we understand not only Earth but the thousands of worlds beyond it.

Final Thoughts

This discovery doesn’t just solve a long-standing mystery—it opens a new chapter in planetary science. The idea that planets can create their own water changes how we think about habitability, planetary evolution, and the origins of life. Instead of being a rare cosmic gift, water may be a common outcome of how the universe builds worlds.

Research Reference:
Experiments reveal extreme water generation during planet formation – Nature (2025)