How many planets have humans landed spacecraft on?
We have sent unmanned probes onto the surfaces of Venus (USSR 1966), Mars (USSR 1971) and Mercury (US 2008). A probe reached Jupiter (US 1972) but it is a gas giant so there is nothing to actually land on, a further probe descended into it's centre and disintegrated (US 1995).
We made our first foray into space by crash landing a probe onto our own Moon (USSR 1959), we have also put a probe down on Saturn's moon Titan (ESA*/US/Italy 2005).
Three other landings have been achieved on lumps of rock in space: Eros (asteroid, US 2001), Comet 9P/Tempel 1 (US 2005) and Itokawa (asteroid, Japan 2005).
We have landed on 3 planets, 2 moons and 3 other celestial bodies.
*European Space Agency