New type of rocky planet with global magma ocean identified by telescope
Astronomers have identified surprising features on the exoplanet L 98-59 d, located 35 light-years from Terra. The celestial body, about 1.6 times the size of our planet, has a density much lower than expected for a purely rocky and metallic composition. Dados obtained by Telescópio Espacial James Webb allowed us to conclude that the interior of the planet is home to a permanent global ocean of magma. Essa structure explains the retention of volatiles such as sulfur and hydrogen over billions of years.
- The planet orbits a small red star in the L 98-59 system
- Spectroscopic observations indicate presence of hydrogen sulfide in the atmosphere
- Computational models confirm fusion fraction of around 45% in the mantle
The discovery was detailed in a study published in the journal Nature Astronomy on March 16, 2026. The low density recorded, close to 2.2 g/cm³ in some estimates, does not fit into conventional models of rocky planets. Instead, it points to an interior rich in molten material that acts as a reservoir for volatile elements.
Internal composition surprises researchers
The planet’s mantle consists of molten silicate, material similar to the lava seen in volcanic eruptions on Terra. Esse magma ocean extends thousands of kilometers deep and remains in a liquid state due to tidal heating and other internal processes. The structure allows sulfur to remain dissolved inside for long geological periods.
The researchers noted that L 98-59 d’s reduced density contrasts with what would be expected for a body of its size. Enquanto to Terra has an average density of approximately 5.5 g/cm³, the exoplanet records significantly lower values. Essa discrepancy led the team to reject water world or gas dwarf scenarios. The best-fitting model indicates a molten mantle capable of retaining volatiles.
The atmosphere rich in hydrogen and hydrogen sulfide complements the internal picture. Radiação ultraviolet radiation from the host star triggers photochemical reactions that produce sulfur dioxide in the upper layers. Esse process resembles the formation of ozone in Terra, but occurs in a chemically reducing and scorching environment.
Imagine a world covered by a permanent ocean of magma that has lasted 5 billion years.
—Galaxies (@Galaxies4k)March 20, 2026
That is L 98-59 d.pic.twitter.com/FGpMgnBmvc
Atmosphere reveals active photochemical processes
Transit spectra captured by James Webb indicate that hydrogen sulfide predominates in the atmospheric composition. The star’s light transforms part of this gas into sulfur dioxide through reactions activated by ultraviolet radiation. The phenomenon confirms the interaction between the molten interior and the outer layers of the planet.
The magma ocean acts as a continuous source of degassing, releasing volatiles that maintain the thickness of the atmosphere. Essa dynamics differ from planets that quickly lose their gases to space. In the case of L 98-59 d, the internal reservoir supports the retention of hydrogen and sulfur for billions of years.
Evolutionary models show that the planet has undergone secular cooling combined with atmospheric erosion. Apesar Furthermore, the molten mantle remains active and preserves a significant fraction of molten material. The configuration explains why the celestial body does not fit into the traditional categories of exoplanets.
Low density points to a reservoir of volatiles
Previous measurements indicated a mass equivalent to 1.64 times that of Terra and a radius of 1.627 times that of Earth. The combination of these values results in a density incompatible with a pure iron core and solid rock mantle. International Equipes adjusted simulations to include high initial sulfur and hydrogen content.
The result reveals that more than 1.8% of the planet’s initial mass may be stored in the form of volatiles. Parte of the hydrogen and carbon migrated into the atmosphere, while the sulfur remains mostly dissolved in the magma. Essa distribution differentiates L 98-59 d from other worlds observed to date.
Astronomers highlight that the planet is close to the so-called “radius ditch”, a region where super-Earths and mini-Neptunes separate into distinct populations. The presence of a permanent magma ocean offers new insight into the mechanisms that shape this division.
Observations from James Webb boost new category
Spectroscopic transit data obtained by the space telescope was combined with observations from ground-based telescopes. The integration allowed refining the exoplanet’s physical parameters and testing multiple composition scenarios. Nenhum dry or water-dominated planet model adequately explained the detected signals.
The team led by Universidade and Oxford researchers concluded that the molten interior represents an alternative evolutionary path for rocky planets. The process involves prolonged retention of volatiles in the mantle, followed by gradual degassing that feeds into the atmosphere. Essa trajectory aligns with trends observed in surveys such as the California-Kepler Survey.
Tidal heating caused by the proximity to the red star contributes to keeping the mantle in a partially molten state. The estimated melting fraction of 45% indicates that a large portion of the silicate remains liquid even after billions of years of planetary evolution.
Implications for understanding rocky exoplanets
The study establishes L 98-59 d as an early example of a previously unidentified class of superheated worlds. Esses bodies combine a scorching surface, a global mantle of magma and an atmosphere enriched by sulfur compounds. The configuration challenges previous classifications based solely on size and density.
Researchers emphasize that internal and environmental processes work together to generate the diversity observed between super-Earths and sub-Neptunes. In the specific case of L 98-59 d, the magma ocean functions as a chemical buffer that regulates the release of gases over geological time.
Future observations with James Webb and other instruments could map variations in the atmosphere and confirm the exact extent of the melt reservoir. For now, the available data already demonstrates that planets with similar characteristics may be more common than previously imagined.
System L 98-59 offers natural laboratory
The exoplanet is part of a system with multiple bodies orbiting the same red dwarf star. The configuration allows direct comparisons between planets of different sizes and compositions within the same stellar environment. L 98-59 d stands out as the outermost of the confirmed planets in the system.
The host star, with less mass and temperature than Sol, radiates energy in a way that keeps the planet in an intense heating zone. Essa orbital proximity favors tidal heating that helps preserve the molten state of the mantle. Astrônomos plan additional observations to refine understanding of entire system dynamics.
The discovery reinforces the role of James Webb as a tool capable of probing the atmospheres and interiors of distant exoplanets with unprecedented precision. Cada new data contributes to reconstructing the processes that form and evolve worlds beyond Sistema Solar.
