There are various pieces of Earth machinery on Mars. Some of it is still functioning. The most active is the recently arrived Mars Phoenix. It has a Twitter feed (what's that?) here. The conceit is that it's really able to answer questions and write grammatical sentences. But undeniably many of the facts in the updates are genuinely originating with Phoenix itself. Sample updates: "I can see Jupiter from here! Saturn's also in view (from Earth too) so I can wave to my buddy @CassiniSaturn (a Twitter newbie)" and "Whoohoo! Was keeping my eye on some chunks of bright stuff & they disappeared! Sublimated! So it can't be salt, it's ice: link"