NASA's Curiosity checked in for the first time on Mars, becomimg the first check-in ever from another planet.

Probably the last possible occurence the founders of Foursquare ever anticipated, Curiosity has checked in with the rather funny line "One check-in closer to being Mayor of Mars."  Alongside this, if ever you were planning on visiting Mars in the Future, Curiosity has even been nice to leave a tip from the Gale Crater:

Mars is cold, dry and rocky. Extra moisturizer and sturdy shoes would be a good idea, plus oxygen for those of you who breathe.

An odd curiosity is further divulging into the location and selecting "get directions," you're given navigation to a set location just outside of Los Angeles.  It might not exactly be on the same 'conspiracy theory' level as filming the moon landing in Nevada; but the truth that is in absolutely no way a glitch of the system since Google hasn't actually mapped mars (yet) is out there!

Source: @MarsCuriosity (Foursquare)

See the big picture about Mars Rover Curiosity