What have our astronauts left behind on...

Well, there’s quite an inventory. Of course, there’s the American flag, left by the first visitor, Neil Armstrong. The first Apollo landing crew also left a commemorative plaque. The remains of seven unmanned lunar probes, Surveyors 1 through 7, are there, plus three lunar rovers. There are six long-term scientific stations on the Moon, which include seismometers to measure tremors in the Moon’s crust and some reflectors to bounce back light beams that we send up there. The Russians left several unmanned probes and assorted lunar rovers on the Moon as well.