A comprehensive review of life as we know it—and may not know it.

In a new paper just published in the journal Universe, Louis Irwin and I attempt to sum up scientists’ current understanding of life “as we know it,” and speculate how life may look and function on alien planets and moons. That includes potential biospheres very different from our own, such as a rocky planet with an ice-covered global ocean. Or it might be a barren planet devoid of surface liquids, or a frigid world with abundant liquid hydrocarbons. It could even be a rogue planet with no “host” star, a tidally locked planet, or a so-called Super-Earth. Maybe the biosphere exists only in the planet’s atmosphere.