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Spectrographs like HARPS can now reach a sub-m/s precision in radial-velocity(RV) (Pepe & Lovis 2008). At this level of accuracy, we start to be confrontedwith stellar noise produced by 3 different physical phenomena: oscillations,granulation phenomena (granulation, meso- and super-granulation) and activity.On solar type stars, these 3 types of perturbation can induce m/s RV variation,but on different time scales: 3 to 15 minutes for oscillations, 15 minutes to1.5 days for granulation phenomena and 10 to 50 days for activity. The highprecision observational strategy used on HARPS, 1 measure per night of 15minutes, on 10 consecutive days each month, is optimized, due to a longexposure time, to average out the noise coming from oscillations (Dumusque etal. 2010) but not to reduce the noise coming from granulation and activity. Thesmallest planets found with this strategy (Mayor et al. 2009) seems to be atthe limit of the actual observational strategy and not at the limit of theinstrumental precision. To be able to find Earth mass planets in the habitablezone of solar-type stars (200 days for a K0 dwarf), new observationalstrategies, averaging out simultaneously all type of stellar noise, arerequired.

Stellar noise and planet detection. I. Oscillations, granulation and sun-like spots