Searches of extrasolar planets towards M31 by gravitational pixel-lensing

The discovery of extrasolar planets (EPs) is certainly one of the most exciting developments in astrophysics during the past decade. The unex- pected variety of giant EPs, many very close to their parent stars and with high orbital eccentricity, has sparked a new generation of astrophysicists to address the question of how planets form and evolve and we are beginning to understand how our solar system fits into a broad community of planetary systems. Among the four main techniques for detecting EPs, microlensing-based searches play a critical role especially for detecting Earth-like planets in the habitable zone. Gravitational pixel-lensing is so powerful that it may allow to detect planets also in other galax- ies. In the present paper we concentrate on the possibility of detecting EPs towards M31 by pixel-lensing using ground-based telescopes and in particular we investigate which is the best suited number of observations per day to maximize the number of planets detectable.