About half the total mass of the Milky Way 's galactic ISM is found in molecular clouds and the galaxy includes an estimated 6,000 molecular clouds, each with more than 100,000 M ☉. The nebula nearest to the Sun where massive stars are being formed is the Orion Nebula, 1,300 light-years (1.2 × 10 km) away. However, lower mass star formation is occurring about 400–450 light-years distant in the ρ Ophiuchi cloud complex.