Mercury in the 9th house indicates a person who seeks something interesting in the realms of philosophy, education, science, and travel.
The 9th house represents worldview, the sphere of religion, higher education, and long-distance travel. Mercury, the planet of thinking, wants to understand things in the smallest details. So, Mercury in the 9th house pushes the person to seek something interesting in these domains.
This individual will tend to analyze any new idea they encounter in depth, not just believing it on face value. It is important for them to verify, to delve into the subject, to do thorough research. It is a very Mercurial approach, more theoretical than practical.
This person really enjoys learning, especially on subjects that interest them. They will use ideas more as a pretext for reflection and discussion rather than for taking action. Themes of philosophy, science, and politics fascinate them. They are curious about other cultures and religions, but will often remain dubious in matters of faith and spirituality, unable to experience them concretely despite their knowledge.
They appreciate travel, not necessarily abroad, but enjoy studying other cultures, for example through documentary programs or readings.