 In December 2010 , a claimed methodological error was reported in the data analysis that led to the discovery of Gliese 581 f and g . The team around Steven Vogt inferred the number of exoplanets by using a reduced chi @-@ square , although the orbital models are nonlinear in the model parameters . Therefore , reduced chi @-@ square is not a trustworthy diagnostic . In fact , an investigation of the fit residuals showed that the data used by Vogt 's team actually prefers a model with four planets , not six , in agreement with the results of Francesco Pepe 's team . 
