[jcrawfordor]

Unfortunately I don't think there's any structured way to determine which planet an article applies to. Broadly speaking, Wikipedia geotagging is inconsistent and the data quality is fairly poor. I think a lot of that is because it's surprisingly difficult to make a viewer like this, so few people have. That makes the data quality issues nonobvious.

Wikidata offers the promise of more structured data, but I know my husband experimented with it and decided not to use it. I think the problem was that mapping Wikidata objects to Wikipedia articles was too difficult (there is a structured way to do this but in practice very few articles have the annotation).

[lambdaone]

The globe: parameter should give you the information you need: see https://en.wikipedia.org/wiki/Template:Coord#globe:G for full documentation on this.