AppStream metadata for the Marble package appear to be missing: https://appstream.debian.org/sid/main/metainfo/marble.html https://appstream.debian.org/sid/main/issues/marble.html This is most likely caused by the desktop icon (marble.png) being in marble-qt-data (which is a dependency of marble-qt which is a dependency of marble). This is not correct - the icon should either be in the main package or in its direct dependency (in this case marble-data). Please, consider fixing this issue to allow easy GUI installation of Marble by non-expert users without forcing them to use a terminal or tools like Synaptic.
Sorry, small typo correction: marble-qt-data (which is a dependency of marble-data which is a dependency of marble)