Starts With A Bang

Finding Earth’s Twin In Space May Be Impossible (Synopsis)

This artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of a star that is similar to our sun. Image credit: NASA / JPL-Caltech / T. Pyle.

“You can spend too much time wondering which of identical twins is the more alike.” -Robert Brault

When we think of the idea of “Earth’s twin,” we inevitably think of a planet like ours orbiting a star like ours at the same distance and speed. Most planets are not rocky and Earth-sized; most stars are not like the Sun; most planetary orbits don’t have Earth’s orbital parameters. Yet the idea that a twin of our planet is out there, and that’s the most likely place to look for life, persists.

Although many of the Earth-like candidates from Kepler are close to Earth in physical size, they may be more like Neptune than Earth if they have a thick H/He envelope around them. Additionally, they predominantly orbit dwarf stars. Image credit: NASA Ames / N. Batalha and W. Stenzel.

Why would that be the case? Of the billions and billions of Earth-sized planets in our galaxy alone, only a very small percentage meet our naive “Earth twin” criteria. Yet there are billions meeting other criteria that may well be habitable, meaning that unless complex life is heavily restricted to worlds around Sun-like stars for hitherto undiscovered reasons, we may be looking for all the wrong things by seeking a twin to our world.

While the brightest stars dominate any astronomical image, they are far outnumbered by the fainter, lower-mass, cooler stars out there. Image credit: NASA/ESA/Hubble/F. Ferraro.

Finding a twin of our world may be practically impossible, and far less useful that we generally assume. The best place to look for life may not be around an Earth-twin at all.