1. Liquid Water
To some, this should have been the first thing on our list. However, you’ll forgive us if we felt it needed to be number one. In order for human life to be possible, liquid water is needed.
This means we do not need planets made of complete ice nor do we need to go to incredibly dry places. We need water we can drink and use long-term. While it does not have to be capable of drinking right out of the ground, it still needs to eventually be possible to drink without bad bacteria in it.