The official number of exoplanets—planets outside our solar system—tracked by NASA has reached 6,000. Confirmed planets are added to the count on a rolling basis by scientists from around the world, so no single planet is considered the 6,000th entry.

Planetary systems in the Milky Way galaxy tend to follow a particular pattern: rocky planets toward the center, closest to the host star, and gas planets toward the exterior. That’s how planets are organized around our sun, with rocky Mercury, Venus, Earth and Mars first in the lineup, followed by the gaseous Jupiter, Saturn, Uranus and Neptune.