1612    Galileo Galilei becomes the first astronomer to observe the planet Neptune, although he mistakenly catalogued it as a fixed star.

1915    Pluto is photographed for the first time but is not recognized as a planet.

1965    Venera program: The Soviet Union launches the Venera 3 space probe toward Venus, the first spacecraft to reach the surface of another planet.

1966    Venera 3 Soviet space probe crashes on Venus becoming the first spacecraft to land on another planet's surface.

1967    Venera program: Venera 4 is launched (it will become the first space probe to enter another planet's atmosphere and successfully return data).

1970    Venera Program: Venera 7 launched. It will later become the first spacecraft to successfully transmit data from the surface of another planet (Venus).

1972    The Pioneer 10 space probe is launched from Cape Canaveral, Florida with a mission to explore the outer planets.

1979    The American space probe ''Pioneer 11'' becomes the first spacecraft to visit Saturn when it passes the planet at a distance of 21,000 km.

1995    51 Pegasi is discovered to be the first major star apart from the Sun to have a planet (and extrasolar planet) orbiting around it.