Final answer:
The environmental factor needed to support life on another planet is liquid water due to its role as a solvent for biomolecules and biochemical interactions.
Step-by-step explanation:
One of the environmental factors that is needed to support life on another planet is liquid water. Life as we know it requires a solvent, a liquid where chemicals can dissolve, which is essential for the formation of biomolecules and the interactions between them. Water has unique properties that our biochemistry relies on, and while it is abundant in the universe, it must be in liquid form to support life. This is only possible within a specific range of temperatures and pressures. Therefore, the search for extraterrestrial life often involves a strategy to "follow the water" which has been applied in assessing habitability on planets like Mars and beyond in our solar system.