The Spitzer search for the transits of HARPS low-mass planets

Radial velocity, microlensing and transit surveys have revealed the existence of a large population of low-mass planets in our Galaxy, the so-called `Super-Earths' and `Neptunes'. The understanding of these objects would greatly benefit from the detection of a few of them transiting bright nearby stars, making possible their thorough characterization with high signal-to-noise follow-up measurements. Our HARPS Doppler survey has now detected dozens of low-mass planets in close orbit around bright nearby stars, and it is highly probable that a few of them do transit their host star. In this context, we have set up an ambitious Spitzer program devoted to the search for the transits of the short period low-mass planets detected by HARPS. We present here this program and some of its first results.