Encyclopedia ofthesolarsystem By Lucy-Ann Adams McFadden, Paul Robert Weissman, Torrence V. Johnson Atreya, S.; Egeler, P.; Baines, K. Water-ammonia ionic
Queloz, N. C. Santos. The HARPS search for southern extra-solarplanets,XVIII. An Earth-mass planet in the GJ 581 planetary system. 2009. arXiv:0906.2780
Mayor, M.; et al, The HARPS search for southern extra-solarplanets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass