Why are we so sure that life requires (liquid) water? Seems a little Earth-centric to me (ie all life we know needs water so all other life must too). Excursions have been made to places like Death Valley or the Atacama Desert to find life that doesn’t use water. The second reason that astronomers are looking for life by looking for water is that you can’t look for something if you don’t know anything about it. So, it’s not that we’re sure that life requires liquid water, we just don’t know what else to look for, and liquid water and life seem to always go hand in hand (here on Earth at least).