As of this writing, the space probe Curiosity has been sending fascinating information about Mars back to earth for over two years. It's hard not to be thrilled by the technological achievement that gives us a glimpse into one of our closest neighbors, and into the universe as a whole. It's only fitting, however, that as we celebrate these victories we also recognize the stumbling blocks that were encountered along the way.

It was on this day, in 1971, that the Soviet Mars 2 space probe landed, or more accurately crash-landed, onto the surface of Mars. The planned landing encountered difficulties - apparently a too steep angle of entry - which prevented the planned soft landing. The probe had returned information to Earth before the attempted landing, but the crash cut off surface communication. It was in this way that the first man-made object to reach the surface of Mars did so, though not exactly as intended. And yet, there should be no doubt that that crash landing, forty years before we were captivated by the photos received from Curiosity, was a significant achievement unto itself, and helped pave the way for the later success.