This article was originally published at The Conversation. The publication contributed the article to Space.com's Expert Voices: Op-Ed & Insights.
When astronomers search for planets that could host liquid water on their surface, they start by looking at a star's habitable zone. Water is a key ingredient for life, and on a planet too close to its star, water on its surface may "boil"; too far, and it could freeze. This zone marks the region in between.
