Lake Stars: From Frozen Lake Patterns to Europa's Hidden Water

In this Short Wave episode, Regina Barber talks with geophysicist Victor Tsai about lake stars—star-shaped melt patterns that form on frozen lakes as warm water seeps through a thin ice layer and slushy snow. The conversation covers how Tsai and colleagues recreated lake stars in a cold lab using a blender to simulate natural slush, and how these patterns relate to spider-like features observed on Europa, one of Jupiter’s icy moons. The discussion also touches on ice safety for people living around frozen lakes and how understanding lake stars could inform future missions to drill into Europa’s possibly accessible water. The episode highlights the interconnectedness of Earth ice physics, planetary science, and space exploration.

Lake Stars: A Window into Ice Physics

This episode introduces lake stars, which are star-shaped melt patterns that emerge when a thin layer of ice is covered by snow and warm lake water seeps up through a small underside hole to melt the slushy snow layer. Regina Barber sits down with Victor Tsai, a geophysicist at Brown University, to unpack the basic physics. Tsai explains that the melt starts with a small circular pattern and, as heat diffuses, arms radiate outward, producing the characteristic star shapes. This is not just a curiosity of winter scenery; lake stars provide a tangible demonstration of heat transfer, diffusion, and channelization of water through ice. The host and guest work through the sequence of events that create these patterns and why the patterns form as a balance of heat input and structural resistance in the ice-snow system.

"The basic idea is just that there's a thin layer of ice with some snow on top of it." - Victor Tsai, geophysicist, Brown University

Lab Experiments: Recreating Lake Stars in a Cold Room

When fieldwork isn’t possible, Tsai describes how he and a collaborator simulated lake stars in a laboratory setting. They created slushy ice on a cold surface using a blender to mimic the natural snow-water-ice interactions, then slowly dripped water slightly above freezing through the slush. This slow drip is crucial; it maintains a constant flow that avoids catastrophically disrupting the slushy layer. Through careful control of temperature and flow, the team observed a progression from a circular melt pattern to branched arms forming a star-like structure as heat diffuses through the ice. The discussion offers practical details for lay listeners who might want to experiment at home, such as using room-temperature water and a gentle drip, and emphasizes that the rate matters to preserve the delicate layered ice structure.

"I purchased a blender." - Victor Tsai, geophysicist, Brown University

Earth and Space: Linking Lake Stars to Europa’s Spider Patterns

The conversation then bridges Earth science and planetary science, focusing on Europa’s surface features. Tsai explains that Europa hosts a spider-like formation on a kilometer-scale that resembles the lake-star patterns seen on Earth. Through lab simulations and modeling, researchers can test whether the same physics could generate such features on Europa, which would imply liquid water being close to the moon’s icy crust at some point in its history. The potential proximity of subsurface water has profound implications for future missions—if water is near the surface, drilling or probing could be more feasible, increasing the likelihood of detecting potential life. The host and guest discuss how these patterns help constrain models of Europa’s interior and inform mission design for probing the near-surface environment.

"If this star pattern really was formed by melted liquid water, then it really suggests that at least at some time in Europa's history you had to have water close to the surface." - Victor Tsai, geophysicist, Brown University

Safety and Public Engagement: What Lake Stars Tell Us About Ice

Finally, the host returns to practical, real-world concerns. Observing lake stars can indicate that nearby ice may be unsafe, especially if lake stars are newly formed, signaling thin ice. Tsai notes that thicker ice forms over time and can preserve lake stars, but wet, newly melted zones may not support weight. The episode closes with a reminder to avoid unsafe ice and to allow conditions to stabilize before stepping onto any lake where lake stars are visible. The show also promotes outreach by pointing listeners to the broader series on lake ice loss and its cultural and ecological impacts.

"If you see one, wait a couple days, then don't go over there until it's been a couple of days." - Regina Barber