How Europa “Breathes”: Science Advances Publishes Article by Matfyz PhD Student

Together with his colleagues, the Czech PhD student with Congolese roots explains how Europa’s surface material is lost and shows that this process—through oxygen transport—may create favorable conditions for extraterrestrial life.

Expansion and contraction of the ice shell

Europa’s surface is covered by an ice shell beneath which lies a salty, liquid water ocean—an environment that may be suitable for life. As a result, Europa has become a primary focus for scientists and space missions such as NASA’s Europa Clipper and ESA’s JUICE.

Using numerical modeling, Martin Kihoulou investigated a process resembling the subduction of lithospheric plates on Earth (where one plate moves beneath another). Europa’s geologically young surface is crisscrossed by extensional bands similar to terrestrial rifts, revealing deeper layers of the ice shell. While areas where ice sinks below the surface cannot be directly observed, they have been partially detected through reconstructions of tectonic motions. For a long time, scientists believed that Europa’s extensional and compressional features balanced each other, conserving the moon’s total surface area—much like Earth’s mid-ocean ridges and subduction zones. However, the forces driving this tectonic deformation and the dominance of extensional features remained unclear.

Europa’s evolution is strongly influenced by its neighboring moons, Io and Ganymede, whose orbits are linked by the so-called Laplace resonance (for every orbit of Ganymede, Europa orbits twice, and Io four times). A classic study by German scientists showed that the eccentricity of these orbits can evolve over hundreds of millions of years, from nearly circular to elliptical. “The more eccentric Europa’s orbit becomes, the more heat is generated in its silicate mantle and ice shell. This heat melts the ice shell, increasing the ocean thickness,” explains Martin Kihoulou.

By modeling this phase transition, the authors found that a fivefold increase in orbital eccentricity could thin the ice shell from 35 km to only 5 km. As the ice melts, Europa’s radius shrinks by about 2 km, generating compressional stress that reaches the yield strength of the ice. This stress causes the shell to fracture, allowing surface layers to sink. When the eccentricity decreases again, the ocean freezes, and the ice shell expands—potentially explaining the current abundance of extensional features. The study suggests that Europa’s tectonic features on a global scale are not driven by internal ice shell dynamics, but rather by its alternating expansion and contraction.

Using a regional model of the ice shell, the researchers further explored the dynamics of this sinking process. They demonstrated that the efficiency of transporting oxygen-rich surface layers depends primarily on the ice shell’s thickness. If the shell is thinner than about 10 km during compression, the sunken ice can reach the subsurface ocean. Such conditions are likely when Europa’s orbital eccentricity increases for at least tens of millions of years.

Conditions suitable for life

This process could significantly enhance Europa’s astrobiological potential. Due to its proximity to Jupiter, Europa is exposed to intense ionizing radiation—harmful to both spacecraft and potential life on the surface. However, this radiation also causes gradual dissociation of ice into oxygen and hydrogen. While hydrogen escapes into space, oxygen molecules may become trapped in the porous upper ice layer. “If this oxygen-rich ice reaches the subsurface ocean—e.g., through subduction—it could alter the water composition and trigger redox reactions,” Martin Kihoulou explains. Given that Europa’s ocean likely contains other essential elements for life—carbon, hydrogen, nitrogen, phosphorus, and sulfur—these reactions, occurring over hundreds of millions of years, could lead to the formation of biomolecules. The seafloor of Europa may thus resemble Earth’s hydrothermal vents, or “black smokers,” which host diverse life forms despite high temperatures and the absence of sunlight.

Martin Kihoulou studied geophysics at the Faculty of Mathematics and Physics at Charles University and also attended the Jaroslav Ježek Conservatory. Since 2021, he has been pursuing a PhD in Physics of the Earth and Planets under a joint supervision program (en cotutelle) between the Department of Geophysics at MFF CU and the Laboratoire de Planétologie et Géosciences at Nantes Université in France.

Martin Kihoulou et al., Subduction-like process in Europa’s ice shell triggered by enhanced eccentricity periods. Sci. Adv. 11, eadq8719 (2025). DOI: 10.1126/sciadv.adq8719

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