Comment on "Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581"

Robertson et al. (Reports, 25 July 2014, p. 440) claimed that activity-induced variability is responsible for the Doppler signal of the proposed planet candidate GJ 581d. We point out that their analysis using periodograms of residual data is inappropriate and promotes inadequate tools. Because the claim challenges the viability of the method to detect exo-Earths, we encourage reanalysis and a deliberation on what the field-standard methods should be.