Almost all of our planets have been explored by some sort of human technology. What were the things we sent to the planets and what was discovered?
MERCURY EXPLORATION: An orbiter, like the one above, was sent to mercury in 2002 and will return in 2011. It is slowly orbiting horizontal and currently is circling vertically before it returns to the space station with pictures of the surface, and perhaps evidence of life.
VENUS EXPLORATION: In 2012 Japan will release Atsuki, another orbiter, into Venus' atmospere. The orbiter will stay halfway between the atmosphere and take samples of what the ozone is made up of.
MARS EXPLORATION: Curiosity is a rover designed to discover if there is or ever was life on Mars. The Sojourner, Spirit, and Oppurtunity have alread completed the task Curiosity is set out to do and returned with little to no evidence. None of the rovers returned with unknown information.
JUPITER EXPLORATION: Juno, a polar orbiter, will study how Jupiter came to look the way it does today by scanning the ground and taking measurments. Juno will help us understand our solar system better.
SATURN EXPLORATION: The Cassini orbiter is on an extended mission. It is exploring Saturns rings, it's atmosphere, and it's moons. Cassini has already landed on and explored Saturns moon, Titan.
URANUS EXPLORATION: Most of what we know about Uranus came from Voyager 2. When it passed by it in 1986 it discoved 10 additional moons and several rings.
NEPTUNE: Voyager II also discoved six more of Neptune's moons.
Great Links and my sources: http://solarsystem.nasa.gov/planets/profile.cfm?Object=Neptune and http://nssdc.gsfc.nasa.gov/planetary/
And a fun game! http://www.kidsastronomy.com/fun/make-a-planet.htm
Have fun learning about our solar system!
