Here we have two beakers both filled with coloured tap water.  To the beaker on the right, we add ordinary table salt, sodium chloride. The sample on the left is just water with food colouring. Next we add dry ice, solid carbon dioxide, to cool the two solutions. Carbon dioxide is solid at any temperature below minus 80 degrees Celsius. Now, we will compare the two samples. The sample on the left, with the salt, has formed a thick slush. The sample on the right without the salt has frozen completely solid.

When the salt dissolves in the water, it breaks into sodium and chlorine ions. The ions diffuse throughout the water and block the water molecules from getting close enough together and in the right orientation to organise into the solid form (ice). However, the water gets colder and the temperature can drop below the freezing point of pure water. Thus, although the ocean at Europa is very cold, it can be sustained as a liquid because it is salty and, thus, the freezing point of water is lowered.

The video supports the Europlanet Icy Moons Collection of Educational Resources - 1. Europa. https://www.europlanet-society.org/outreach/educational-resources/icy-moons-collection-1-europa/

Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149.