For Earth-like Planets, You Need the Right Galactic Environment

Editor's Note: As a series at ENV, we are pleased to present "Exoplanets." Daniel Bakken is anengineer who teachesastronomy at the college level, and an entrepreneur in compound semiconductor crystal growth. In a series of articles he critically examines recent claims about exoplanets beyond our solar system, asking whether our own planet Earth is a rarity, or common, in the cosmos. For previous articles in the series, see here.

The galactic environment contributes to habitability in several...