Space probes have gone near or landed on all planets in our solar system. In recent decades better telescopes have found planets in solar systems other than our own, which are known as exoplanets. One of the first was a planet found to be orbiting Barnard's star.
Planetary science in a broad sense includes finding a planet's orbital period and orbital distance from its star, the mineral makeup of the planet, and an attempt to learn its age. It may also have a more narrow focus, such as the mapping of the planet's surface features and the makeup of its atmosphere.