Zackrisson’s work suggests an alternative to the commonly held assumption that planets similar to Earth must exist, based on the sheer number of planets out there. Ever since Copernicus put forth the theory that Earth is not the center of the universe, scientists have expanded the map of the cosmos and diminished our planet’s relative uniqueness. Current estimates hold that there are some 100 billion galaxies in the universe containing about 10^18 stars, or a billion trillion.

One of the most fundamental requirements for a planet to sustain life is to orbit in the “habitable zone” of a star — the “Goldilocks” region where the temperature is just right and liquid water can exist. Astronomers have, to this point, discovered around 30 exoplanets in the habitable zones of stars. Simply extrapolating that figure based on the known number of stars suggests that there should be about 50 billion such planets in the Milky Way alone. Probability seems to dictate that Earth-twins are out there somewhere.

But according to Zackrisson, most planets in the universe shouldn’t look like Earth. His model indicates that Earth’s existence presents a mild statistical anomaly in the multiplicity of planets. Most of the worlds predicted by his model exist in galaxies larger than the Milky Way and orbit stars with different compositions — an important factor in determining a planet’s characteristics. His research indicates that, from a purely statistical standpoint, Earth perhaps shouldn’t exist.