PLATO mission: how many Earth-like planets could an autoregressive method detect?

Thousands of simulated light curves show that an autoregressive detection method would identify at least half of the short-period, Earth-sized planets after just three months of observation.

The European PLATO mission, which has to track down small rocky planets around bright stars, will have to deal with the magnetic activity of these stars, a source of parasitic signals. A study published on arXiv evaluates its sensitivity to planets of 0.5 to 2 terrestrial rays using the ARPS method (AutoRegressive Planet Search), which filters non-global variations by self-regressive modelling and then searches for transits with a dedicated periodogram.

Contrasting results

Several thousand simulated light curves were analyzed for the LOPS2 field in which transits were injected. In the first three months of observation of bright stars, at least 50% of Earth-sized planets are found for periods of less than 40 days. Over two years, 25% are for periods of less than 240 days.

Researchers recognize that the method is not perfectly suited to PLATO, but their results shed light on the compromises between sensitivity and false alarms, and offer a positive predictive value card to judge the reliability of detections after verification.