June 2, 2023 marks the 20th anniversary of the launch of the European space probe Mars Express. Mars Express is considered one of the most successful space missions ever sent to our neighboring planet. On board is the German "High Resolution Stereo Camera" (HRSC), which has been continuously recording images from Mars orbit ever since. The data stream from the HRSC has yielded a multitude of new insights in recent years. Gerhard Neukum (1944-2014) led the development of the HRSC, which is designed to perform global mapping of Mars at 12m resolution, providing simultaneously colour images of the surface and its topography. The HRSC was first installed on the Russian Mars 96 probe, which unfortunately failed to leave Earth's orbit after launch and burned up in the atmosphere. But Gerhard Neukum kept going, as director of the DLR Institute for Planetary Research in Berlin Adlershof, he became the key proponent for the first ESA research probe to be sent to another planet. In 2002, Gerhard Neukum moved to Freie Universität as a professor, where he established the Department of Planetary Sciences and Remote Sensing.