Earth-sized

Kepler has found that smaller planets (Earth-sized rather than Jupiter-sized) are likely to be the most common in the Milky Way galaxy.

Source: tatoeba (6285296)

Even if a planet is rocky, Earth-sized, and just the right distance from its star, it also must have an atmosphere that contains the correct ingredients to foster and sustain life.

Source: tatoeba (6285305)

Basic physics tells us that smaller planets must be rocky and larger ones gaseous, but for planets ranging from Earth-sized to about twice that radius, astronomers can't tell a large rocky planet from a small gaseous planet.

Source: tatoeba (6547954)

Scientists at the Harvard-Smithsonian Center for Astrophysics, after analyzing data from NASA's Kepler space telescope, calculated that six percent of the galaxy's 75 billion red dwarf stars have potentially habitable, Earth-sized planets. Red dwarfs — which are smaller, cooler and much dimmer than our own Sun — are the most common stars in the galaxy, so the closest Earth-like planet could be just 13 light years away, the astronomers conclude in their new study.

Source: tatoeba (12158646)