First moon outside our solar system discovered


  • Astronomers have pinpointed what appears to be the first moon detected outside our solar system, a large gaseous world the size of Neptune that is unlike any other known moon and orbits a gas planet much more massive than Jupiter.


  • Known as an exomoon because it is outside our solar system.
  • Our solar system’s moons all are rocky or icy objects. The newly discovered exomoon and the planet it orbits, estimated to be several times the mass of our solar system’s largest planet Jupiter, are both gaseous, an unexpected pairing. They are located 8,000 light years from Earth.
  • The exomoon is exponentially larger than our solar system’s biggest moon. Jupiter’s moon Ganymede has a diameter of about 5,260 km. The exomoon is estimated to be roughly the size of Neptune, the smallest of our solar system’s four gas planets, with a diameter of about 49,000 km.
  • The exomoon and its planet orbit Kepler-1625, a star similar in temperature to our sun but about 70% larger. The exomoon orbits roughly 3 million km from its planet and its mass is about 1.5% that of its planet.


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