This is a good week for space exploration buffs like me. There’s a literal traffic jam in orbit and on the surface of planet Mars as three new arrivals complete their 300-million-mile sojourns from Earth at the same time, celestially speaking. Two of the new arrivals will remain in orbit, bringing to 14 the total number of unmanned spacecraft circling the planet. Six are active and collecting scientific data. The other eight, sent beginning in 1971, quietly circle, their sources of power or ability to operate long since expired. The third new…