Andrew W. Howard; John Asher Johnson; Geoffrey W. Marcy; Debra A. Fischer; Jason T. Wright; Gregory W. Henry; Howard Isaacson; Jeff A. Valenti; Jay Anderson; Nikolai E. Piskunov (2010). "The NASA-UC Eta-Earth Program: II. A Planet Orbiting HD 156668 with a Minimum Mass of Four Earth Masses". The Astrophysical Journal. 726 (2): 73. arXiv:1003.3444v1. Bibcode:2011ApJ...726...73H. doi:10.1088/0004-637X/726/2/73. S2CID15559379.
Andrew W. Howard; John Asher Johnson; Geoffrey W. Marcy; Debra A. Fischer; Jason T. Wright; Gregory W. Henry; Howard Isaacson; Jeff A. Valenti; Jay Anderson; Nikolai E. Piskunov (2010). "The NASA-UC Eta-Earth Program: II. A Planet Orbiting HD 156668 with a Minimum Mass of Four Earth Masses". The Astrophysical Journal. 726 (2): 73. arXiv:1003.3444v1. Bibcode:2011ApJ...726...73H. doi:10.1088/0004-637X/726/2/73. S2CID15559379.
Andrew W. Howard; John Asher Johnson; Geoffrey W. Marcy; Debra A. Fischer; Jason T. Wright; Gregory W. Henry; Howard Isaacson; Jeff A. Valenti; Jay Anderson; Nikolai E. Piskunov (2010). "The NASA-UC Eta-Earth Program: II. A Planet Orbiting HD 156668 with a Minimum Mass of Four Earth Masses". The Astrophysical Journal. 726 (2): 73. arXiv:1003.3444v1. Bibcode:2011ApJ...726...73H. doi:10.1088/0004-637X/726/2/73. S2CID15559379.
Andrew W. Howard; John Asher Johnson; Geoffrey W. Marcy; Debra A. Fischer; Jason T. Wright; Gregory W. Henry; Howard Isaacson; Jeff A. Valenti; Jay Anderson; Nikolai E. Piskunov (2010). "The NASA-UC Eta-Earth Program: II. A Planet Orbiting HD 156668 with a Minimum Mass of Four Earth Masses". The Astrophysical Journal. 726 (2): 73. arXiv:1003.3444v1. Bibcode:2011ApJ...726...73H. doi:10.1088/0004-637X/726/2/73. S2CID15559379.