How to Search for Extra-Solar Planets with the VLT/VISA?

Abstract

We review the motivation for searching for Extra-Solar planets, and point out that we really do not know if the Solar System is a common place or a rare stellar system. A weak version of the Anthropic Principle prevents us from applying the Copernicus Principle to deduce that there are many other planetary systems similar to ours. We consider the different possibilities to search for exo-planets: (i) direct methods, where one has to beat the huge contrast between the stellar flux and that of the planet (10¹⁰ in the visible for the Sun/Earth system); (ii) indirect ones, where the stellar motion or photometry are studied, looking for perturbations due to possible planets. The indirect methods can be of different types: differential astrometry, radial velocimetry, (pulsar) timing and precise photometry. We show that the VLT and VLTI have remarkable astrometric and velocimetric potential for searching for Jovian planets around a large sample of stars of many types, including solar-like ones. We conclude that Europe should not miss the start of a key field for 21^st century Astrophysics and should begin to build the appropriate instruments.