The biggest changes to the Institute resulted from German unification with the retraction of two of the four directors of the institute in 1998 and 2004 after the retirement of Hagfors and Rosenbauer. The institute was renamed "Max Planck Institute of Solar System Research" in 2004 after the last director concerned with Ionosphere and Stratosphere research retired. The two remaining groups, of director S. Solanki dedicated to the sun and heliosphere and of U. Christensen dedicated to planets and comets form the present-day Institute.