Short Wave

An icy mystery: What are lake stars?

March 13, 2026

Key Takeaways Copied to clipboard!

  • Lake stars are star-shaped, dark, branching patterns in ice formed when warm lake water seeps through a hole in the ice layer, melts a slushy snow layer, and spreads out. 
  • Geophysicist Victor Tsai scientifically proved the formation of lake stars by recreating them in a lab using a blender to make slush and carefully dripping slightly warm water through it. 
  • Studying lake stars on Earth provides a potential model for understanding star-like (or spider) patterns observed on Jupiter's icy moon Europa, which could offer clues about the historical proximity of liquid water to Europa's surface. 

Segments

Producer’s Icy Observation
Copied to clipboard!
(00:00:00)
  • Key Takeaway: Producer Berly McCoy observed unsettling, dark, spidery, star-shaped patterns in the ice on a frozen lake.
  • Summary: Producer Berly McCoy was alarmed by dark, spidery, star-shaped patterns she saw in the ice on a frozen lake during a weird winter. She had never encountered this phenomenon before, despite spending significant time on the ice. The podcast brought in an expert to identify this icy feature.
Lake Star Identification and Expert Introduction
Copied to clipboard!
(00:00:42)
  • Key Takeaway: Geophysicist Victor Tsai identified the phenomenon as a lake star and is the first to scientifically prove its formation mechanism.
  • Summary: The phenomenon observed by the producer is called a lake star, according to geophysicist Victor Tsai of Brown University. Tsai studied lake stars as a visiting graduate student at Woods Hole Oceanographic Institution. He successfully figured out the science behind their formation by creating them in a laboratory setting.
Lake Star Formation Explained
Copied to clipboard!
(00:01:40)
  • Key Takeaway: Lake stars form when snow depresses thin ice, allowing warm lake water to seep up through a small hole, melt the snow layer, and create branching melt patterns.
  • Summary: Lake stars require a thin layer of ice with snow on top, which pushes down on the ice. A small hole in the underside of the ice allows warm lake water to seep upward. This water melts through the slushy snow layer, eventually forming the characteristic star patterns.
Lab Recreation of Lake Stars
Copied to clipboard!
(00:02:17)
  • Key Takeaway: Victor Tsai recreated lake stars in a cold lab by using a blender to make slushy snow and dripping slightly warm, near-freezing water through it slowly.
  • Summary: Since fieldwork was impossible in the summer, Tsai created miniature lake stars in a cold lab. He purchased a blender to create a slushy snow layer similar to those found in nature. The water must be dripped slowly, like a leaky faucet, to prevent the slush layer from catastrophically breaking up.
Home Experiment Instructions
Copied to clipboard!
(00:04:16)
  • Key Takeaway: Individuals can replicate lake stars at home using a kitchen blender for slush and pouring slightly warm (ideally below room temperature) water through it slowly.
  • Summary: To make lake stars at home, one should use a kitchen blender to form slush and place it on a flat surface. Slightly warm water, preferably below room temperature, should be poured through the slush pattern. The water must drip slowly to allow circular melt patterns to expand and form branching star shapes within a few minutes.
Europa’s Spider Feature Connection
Copied to clipboard!
(00:06:12)
  • Key Takeaway: A mile-wide, star-like ‘spider pattern’ on Europa’s icy surface may have formed via the same physics that create terrestrial lake stars.
  • Summary: A formation on Europa, previously called a spider pattern, is very similar to the lake stars discussed. This feature is massive, measuring one to two kilometers wide, far larger than the 30-foot maximum size seen on Earth. The theory explaining Earth’s lake stars can approximately explain the formation observed on Europa.
Implications for Europa Water Search
Copied to clipboard!
(00:08:32)
  • Key Takeaway: If Europa’s star pattern formed from melted liquid water, it suggests water was once close to the surface, which is critical for planning future drilling missions.
  • Summary: The presence of such a feature suggests that, at some point in Europa’s history, liquid water had to be close to the surface. This matters for future missions because drilling success depends on the depth of the water layer; if it is 40 kilometers thick, drilling is unlikely, but if it is near the surface, sampling becomes feasible.
Lake Star Safety Implications
Copied to clipboard!
(00:10:15)
  • Key Takeaway: Recently formed lake stars indicate unsafe ice conditions because they form when the ice is thin and covered in slush, though older, preserved stars may exist under thicker, safer ice.
  • Summary: If a lake star has recently formed, the ice is very unsafe because it is thin and covered mostly by snow and slush, unable to support weight. However, many observed lake stars are preserved under thicker ice that formed later. If one sees a lake star, waiting a couple of days for thicker ice to form is advised before walking over the area.