In a surprise, first alien moon discovered is big and gaseous

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. "It's big and weird by solar system standards," Columbia University astronomy professor David Kipping said of the moon, known as an exomoon because it is outside our solar system. 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.