The Oort cloud (/ˈɔrt/ or /ˈʊərt/) or Öpik–Oort cloud, named after Dutch astronomer Jan Oort and Estonian astronomer Ernst Öpik, is a theoretical spherical cloud of predominantly icy planetesimals believed to surround the Sun at a distance of up to around 100,000 AU (2 ly). This places it at almost half of the distance to Proxima Centauri, the nearest star to the Sun, and in interstellar space.