Albedo

Albedo measures how much incoming light a surface reflects, on a scale from 0 (absorbs everything) to 1 (reflects everything).

Earth's overall albedo is about 0.3, meaning it reflects roughly 30% of the sunlight that reaches it. Fresh snow and ice can reflect 80% or more; open ocean reflects less than 10%. Venus, covered in bright clouds, has a very high albedo, yet is still the hottest planet because of its greenhouse atmosphere.

Albedo matters for climate: more ice means more reflected sunlight and further cooling, a feedback that can drive a planet toward a “snowball” state.

Read more in Step 2: Choosing the orbit.