Final answer:
Water is the element that is liquid on Triton, and its freezing temperatures have significant effects on the planet's surface features.
Step-by-step explanation:
The element that is liquid on the planet Triton is water. The surface material of Triton is made up of frozen water, nitrogen, methane, and carbon monoxide. Water, which is usually a liquid on Earth, is frozen on Triton due to its extremely cold temperatures.
This affects surface features on Triton in various ways. For example, the frozen water contributes to the formation of a polar cap in the southern hemisphere, which evaporates along the northern edge. The freezing of water and other compounds also impacts the geological evolution of Triton, leading to regions of flooded terrain and mountainous areas.
In summary, water is the element that is liquid on Triton, and its freezing temperatures have significant effects on the planet's surface features.