For the first time, astronomers have discovered an exoplanet outside our Milky Way galaxy.

This world, the size of Earth’s moon, orbits a sun-like star in our local Milky Way galaxy, and this galactic group may be home to alien life.

There are billions of stars in our galaxy, but only when a star crosses our solar system can we detect life on its planet.

Why did we find this exoplanet?

Researchers identified this exoplanet by studying the light from a star that is only 2.6 billion miles away, but which is similar to our Sun.

They were watching for a change in the dimming of a star’s light as a planet passed between Earth and the star – when the planet disappeared from view.

Their observations from 2015 to 2016 show that the planet is 1.6 times the diameter of Earth and orbits its star at a distance of 40 million miles from it.

How big is the exoplanet?

The exoplanet is 750 million kilometers from its star – roughly the distance from Earth to Jupiter. The moon is 160 million kilometers from our planet.

I wondered how planets in this system might become habitable.

While it is possible for this planet to be tidally locked to its star, an old joke in astronomy is that you can choose your sun based on how well your left eye talks to your right eye.

It turns out that this planet would actually be a great home for possible life outside the Milky Way. The properties of exoplanets allow for extensive exploration through telescopes and other higher precision instruments.

Why look for exoplanets?

All planets outside our solar system are potentially habitable, but their presence is usually detected only when a massive planet passes in front of its star, blocking more stellar light than the star’s natural brightness varies.

The researchers speculate that the exoplanet may be a rocky planet with a thick atmosphere and may be in the process of growing, as it spins in an elliptical orbit rather than the circular orbit of our own solar system.

Sarah Pierce, principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said, “What’s surprising about this discovery is how similar its features are to our sun.”

Planets of this size are likely to be common only in the Milky Way’s Local Group of galaxies, a cluster of nearly 100 Sun-like stars in the Perseus cluster.

The Exoplanet Hunters project is funded by NASA’s Exoplanet Exploration Program.