Imagining Other Earths

Imagining Other Earths is David Spergel's Princeton course on the question of whether we are alone. It introduces core concepts from astronomy, biology and planetary science so that you can speculate scientifically about life elsewhere and invent your own solar systems. Its twenty-five short modules move from the size of the universe and the definition of life through the planets, moons and small bodies of our solar system and their atmospheres, to the search for extrasolar planets using Kepler's laws, transits, microlensing and imaging, the properties and evolution of stars, the formation of the Earth and the origin of water, the biochemistry and origin of life, extremophiles and extinctions, and finally what makes a planet habitable, the habitable zone, the Fermi paradox and SETI.

Coursera lists a flexible schedule and estimates three weeks at ten hours a week; no level is given. The page states that all the features of the course are available for free and that it does not offer a certificate upon completion.