Lava planets, those enigmatic celestial bodies that defy the norms of our solar system, have long intrigued scientists. These scorching-hot worlds, some no bigger than Earth, orbit their stars so closely that a full year lasts less than a day. With surfaces hot enough to melt and even vaporize rock, they present conditions unlike anything familiar on Earth, Mars, or Venus. Yet, it is precisely their extreme environments that make them ideal candidates for exploring how rocky planets evolve.
A groundbreaking study published in Nature Astronomy and led by Charles-Édouard Boukaré, a physics professor at York University, offers a new framework to understand how these exotic planets change over time. The research combines geophysics, atmospheric science, and mineral chemistry to examine the interactions between molten rock, vapor, and solid crust over billions of years. According to Boukaré,
“Lava planets are in such extreme orbital configurations that our knowledge of rocky planets in the solar system does not directly apply.”
A Tale of Two Interiors
The researchers employed complex numerical simulations to explore the evolution of these planets. Two extreme interior states emerged from the models. The first scenario pertains to younger lava planets with fully molten interiors, where the atmosphere mirrors the planet’s composition. Heat circulates efficiently beneath the surface, maintaining an active and hot nightside.
In contrast, older planets present a different picture. Their interiors have largely solidified, leaving only a shallow magma ocean on the dayside. The atmosphere in this case becomes chemically altered, with elements like sodium, potassium, and iron disappearing over time, either absorbed into the crust or lost to space. The nightside cools into a quiet, solid slab.
These two end-member states provide scientists with a method to infer a planet’s age and internal chemistry based on observations from afar. Due to their short orbits and locked rotations, lava planets always show one face to their star, allowing astronomers to clearly view both the fiery dayside and the frozen nightside.
The Chemistry of Melting Worlds
At the core of this new framework is the concept of chemical distillation. When rock melts or vaporizes, certain elements prefer specific phases. For instance, magnesium and silicon often remain in the liquid or solid, while lighter elements like sodium and potassium escape more easily into vapor. Over time, this cycle of melting, vaporizing, and solidifying continuously reshapes a planet’s outer layers.
Boukaré notes,
“These processes, though greatly amplified in lava planets, are fundamentally the same as those that shape rocky planets in our own solar system.”
The team discovered that chemical fractionation between solid and liquid rock could lead to significant changes in surface and atmospheric composition. While similar processes are evident in ancient lava flows and planetary crusts on Earth, on a lava planet, this mixing and separation occur continuously for billions of years due to constant exposure to extreme heat and vacuum.
Modeling with Fresh Eyes
The simulations did not start with bold claims. Boukaré admits the work began as a highly exploratory effort. His earlier studies with collaborators at Université Paris Cité had developed models of molten rocky planets, but they had not yet applied them to these unique exoplanets.
This time, the team incorporated a broader set of expertise. Co-authors include researchers from McGill University, University of St Andrews, University of Waterloo, and Université Paris Cité. Their combined effort created what Boukaré calls a “conceptual framework for interpreting evolution,” enabling scientists to link atmospheric data to internal processes.
To support the study, the team secured 100 hours of observation time with the James Webb Space Telescope (JWST). The JWST’s powerful infrared sensors will allow scientists to detect the chemical makeup of lava planet atmospheres, confirming or refuting predictions from the models. Lead observations will be conducted by Prof. Lisa Dang of the University of Waterloo.
Boukaré explains,
“If we can observe and distinguish old lava planets from young ones, it would mark an important step toward moving beyond the traditional snapshot view of exoplanets.”
Winds, Waves, and Magma Oceans
The planet’s tidally locked state creates an unusual surface dynamic. While the dayside remains molten, the nightside cools into solid crust. Winds generated by the stark temperature contrast sweep vapor and heat across the planet, influencing how materials move between hemispheres. Earlier studies had examined these supersonic winds and their effect on magma oceans, but they omitted a critical aspect—how the molten rock interacts with the solid mantle beneath.
This study takes that next step, focusing not just on surface behavior but also on how the entire silicate interior behaves. Rock-forming elements like magnesium, silicon, and iron behave differently in molten and solid states. Incompatible elements remain in the melt, accumulating over time and altering the chemical fingerprint of the magma ocean.
For a lava planet, the melt never fully disappears. Unlike magma oceans in our own solar system, which freeze within hundreds of millions of years, lava planets maintain their magma oceans for billions of years. This provides ample time for long-term chemical separation between vapor, liquid, and solid.
A Planet’s Life Story in Its Atmosphere
The ability to peer into the internal state of a planet by analyzing its atmosphere is a game-changer. JWST will allow astronomers to test whether elements like sodium and potassium appear in the vapor above lava planets. Their absence could indicate a more evolved, solidified interior, while their presence would suggest a younger, still-molten world.
These insights extend beyond lava planets, aiding scientists in understanding how rocky worlds evolve more generally, including Earth-like planets in other solar systems. While lava planets are too hot to host life, they serve as ideal laboratories for testing how rock and atmosphere interact over long timescales. With JWST’s observations on the horizon, these molten exoplanets are likely to become a focal point in the near future.
