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Stellar activity produced by spots and plages affects the radial velocity(RV) signatures. Because even low activity stars would produce such a signal,it is crucial to determine how it influences our ability to detect smallplanetary signals such as those produced by Earth-mass planets in the habitablezone (HZ). In a recent paper, we investigated the impact of sunlike spots. Weaim here to investigate the additional impact of plages. We used the spot andplage properties over a solar cycle to derive the RV that would be observed ifthe Sun was seen edge-on. The RV signal comes from the photometric contributionof spots and plages and from the attenuation of the convective blueshift inplages. We compared the RV signal with the signal that would be produced by anEarth-mass planet in the HZ. We find that the photometric contributions ofspots and plages to the RV signal partially balance each other out, so that theresidual signal is comparable to the spot signal. However, the plagecontribution due to the convective blueshift attenuation dominates the totalsignal, with an amplitude over the solar cycle of about 8-10 m/s. Thiscontribution is very strongly correlated with the Ca index on the long term,which may be a way to distinguish between stellar activity and a planet.Providing a very good temporal sampling and signal-to-noise ratio, thephotometric contribution of plages and spots should not prevent detection ofEarth-mass planets in the HZ. However, the convection contribution makes such adirect detection impossible, unless its effect can be corrected for by methodsthat still need to be found. We show that it is possible to identify theconvection contribution if the sensitivity is good enough, for example, byusing activity indicators.

Using the Sun to estimate Earth-like planets detection capabilities II. Impact of plages