tokens: of K2-140b in Livingston et al. ( 2018 ) was based on simple mass–radius relation. It was not the intention to give accurate mass determinations, rather to select appropriate targets for follow-up observations. This highlights the importance of RV measurements to determine precise planetary masses. The planet mass derived by G18 using RV measurements is in agreement with the presented results within 1σ. The main difference between the subsequent analysis and the parameters for K2-140b from G18 is the orbital eccentricity. An accurate estimate of this parameter is important since it affects the derived argument of pericentre, stellar mean density, semimajor axis, and thus the derived equilibrium temperature. G18 found a non-zero eccentricity for K2-140b of using 12 CORALIE and 6 HARPS RV measurements. The analysis presented in this paper favours in contrast a circular orbit solution. In order to check whether this is a direct result from the additional 13 RV measurements the relation for an expected eccentricity error σ( e ) (Zakamska et al 2011) is used: where K is the radial velocity amplitude, N is the number of RV observations, and σ obs is the average RV error of the observations. The G18 RV data with K = 111.2 m s −1 , σ obs = 23.6 m s −1 , and N = 18 do not constrain the orbit eccentricity better than σ( e ) = ±0.21. The KESPRINT RV data with K = 102 m s −1 , σ obs = 12.8 m s −1 , and N = 13 constrain the orbit eccentricity to σ( e ) = ±0.15. Combining both data sets ( K = 106 m s −1 , σ obs = 19.1 m s −1 , and N = 31), the orbit eccentricity is constrained to σ( e ) = ±0.14. Thus it was concluded that the more accurate KESPRINT RV measurements improved the eccentricity detection. Moreover, a combined fit using the light curve and the RV data achieves better accuracy in the eccentricity. The eccentricity found by G18 might be driven by the uncertainties of the individual RV measurements and their distribution along the RV curve. The significance of their result was here tested statistically by Monte Carlo simulations. One hundred thousand simulated RV data sets were created by sampling a best-fitting circular orbit solution at the timestamps of the CORALIE and HARPS observations. Gaussian noise at the same level of the G18 measurements was added. A least-squares fit to these simulated data also allowed an eccentric solution. There is a probability of ∼12 per cent that an eccentric solution with e ≥ 0.12 may be found if the true orbit is actually circular. The same analysis was repeated by combining the FIES RV data with those from G18 . Once again, simulated data created from the best-fitting circular orbit model can mimic an eccentric orbit with a probability of 6 per cent. The new analysis shows that the previously claimed eccentric orbit is not statistically significant. In contrast, the BIC that distinguishes between an eccentric or circular solution prefers the circular orbit. The results highlight the difficulty in distinguishing
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