An artist made this image to show the different types of planets that have been detected circling stars in our galaxy. (AP)

Our Milky Way galaxy is home to at least 17 billion planets that are similar in size to Earth, a new estimate suggests. That’s more than two Earth-size planets for every person on the globe.

The estimate is the first reliable tally of the number of worlds outside the solar system that are the size of Earth, but the hunt for a real twin of our planet is far from over.

Despite a big increase in planet discoveries in recent years, scientists still are looking for one that’s not only the right size but also in the so-called Goldilocks zone, where it’s not too hot and not too cold for water to be in liquid form on the surface.

Scientist Francois Fressin and his team examined data collected by NASA’s Kepler spacecraft. The Kepler spacecraft continues to spot planets as they pass between Earth and the star they orbit.

Fressin said it’s clear that there are plenty of rocky planets outside the solar system.

“If you look up on a starry night, each star you’re looking at — almost each one of them — has a planetary system,” Fressin said.