Extrasolar Planets - the question whether there are other worlds like the Earth, and whether such planets may harbor life, forms the basis of one of the most fascinating research topics today. In 1995, the first planet to orbit a star other than the sun was found, and since then hundreds of extrasolar planets have been discovered. Snellen's research focuses mainly on transiting planets. Once per orbit they cross the disk of their host star, which allows for a detailed study of their atmospheres. It is hoped that the techniques developed now can soon be applied to planets like Earth, to establish whether they harbor life.

Snellen develops observation and data-reduction techniques for ground-based telescopes, particularly geared to be used for the future extremely large telescopes (ELT). For this they concentrate on optical and near-infrared secondary eclipse photometry and transmission spectroscopy. Most of the time, the telescopes on La Palma (Canary Islands, Spain) and those from the European Southern Observatory (La Silla & Paranal, Chile) are used for this research. The team also develops a new camera-system to find the brightest transting planets in the sky, MASCARA.