On September 29, 2010, astronomers using the Keck Observatory proposed two additional planets, Gliese 581f and Gliese 581g, both in nearly circular orbits based on analysis of a combination of data sets from the HARPS and HIRES instruments.
Using the assumption that the noise present in the data was correlated (red noise rather than white noise), Roman Baluev called into question not only the existence of planet g, but Gliese 581d as well, suggesting there were only three planets (Gliese 581b, c, and e) present [REF].