Sara Seager speaks of the habitable zone, the area around a given star where scientists expect to find exoplanets with appropriate conditions to harbor life. A habitable planet is defined by the possibility of finding liquid water at its surface. Planets too far away from their stars are too cold, planets too close are too hot. Historically, the habitable zone has been estimated using several models, according to the limits where liquid water is a possibility. Seager suggests some of these models may be inaccurate, and too narrow-minded. The existence of hydrogen-atmosphere planets, rogue planets, and dry planets suggests that the habitable zone may be larger than predicted. The controversial role of water in planet formation provides further evidence for this theory.

The process of finding “earth-like planets” is no small task. Exoplanet detection techniques are numerous, and the future is full of promise. Seager introduces TESS, the upcoming satellite mission that seeks to track the entire sky for exoplanets in a period of two years. The James Webb telescope will help astronomers track atmospheres for TESS’s yield. The external coronagraph, a deployable starshade that will block-out star light to clear visibility, will reveal new habitable bodies. With exciting new possibilities, the quest for habitable “earth-twins” continues.

For an overview of exoplanet detection techniques, see: Exoplanet Detection: Techniques I and Exoplanet Detection: Techniques II.