Imagine viewing a web page with a reference to a landing site on Mars - and being able to use an add-on to your browser to be taken directly to that site, in a 'Martian' mapping application of your choosing, or on a site like Google Mars. Or being able to search, easily, for web sites referring to the same site, without seeing places on Earth with co-incidentally similar coordinates.
Those are just two of the things a "mars" microformat, based on the existing Geo version, might do for you.
This is especially relevant now that the Mars Reconnaissance Orbiter is getting some publicity. It would be useful to be able to markup photographs, findings, reports, etc.
Here's some work-in-progress:
- luna - the same sort of thing, for The Moon