He studies (exo-)planets, solar and stellar magnetic fields, aerosols and trace gases in planetary atmospheres and develops innovative optical instruments for astronomy, remote sensing and biomedical imaging. He has authored or co-authored more than 350 publications and received the Friedrich Wilhelm Bessel award for outstanding research in astrophysics as well as the Netherlands Academic Year Prize for outreach. Keller’s group is world leading in the development of high-accuracy polarimetric instrumentation for astronomy and environmental sensing where they achieve order-of-magnitude performance gains with novel optical techniques. These developments lead to breakthrough observations with instruments at the world’s largest telescopes and enable the latest space instruments for climate science. Interests Exoplanetary systems and solar system Innovative optical instrumentation Solar physics Remote sensing of aerosol and trace gases Interdisciplinary research