The planet's atmosphere was analyzed when it passed in front of its host star as some of its infrared light passed through the planet's atmosphere. (members.nova.org)
The transit method works by waiting for a planet to pass in front of its host star. (spaceflightinsider.com)
Back in the day, we could only determine whether a planet had water by watching it pass in front of its host star during orbit, or by collecting imaging data from planets far enough away from their host stars [source: Caltech]. (science.howstuffworks.com)