I think this is an excellent use of subpages. This makes it possible to link to "Mercury" and get something that is relevant without knowing the naming idiosyncracies beforehand. Putting all this on one page seems out of the question since at least the first three of the four subsubjects would be pretty long articles.
I'd prefer a layout like this, though:
1. Mercury is the innermost planet circling the Sun.
2. Mercury is a chemical element with atom number ...
3. Mercury is the God of ... in the Roman mythology.
4. Mercury is a programming language used for ...
Each subsubject should have an introduction of a sentence or two (all of them should fit on a page). A little more than now, but not too much. --Pinkunicorn