Mercury - The innermost, fastest, and smallest solar system planet, known to the ancients as two different planets. It is composed mostly of a large iron core. It rotates three times for every two orbits around the Sun. Its daytime side is one of the hottest places in the solar system, while its night side is one of the coldest. One of the only rocky bodies known to have its own magnetic sphere. Has a minimal atmosphere and no moon. Visited by the Mariner 9 spacecraft three times and is currently orbited by Messenger. Several other international missions are planned.
Venus - The second planet from the sun and the hottest. The brightest object in the sky other than the sun and moon, it was once known as the evening and morning star. Has an atmosphere rich in Carbon Dioxide and a runaway greenhouse. Has extreme surface pressure, continent-sized highlands, and soft, gooey surface of melted rocks. Once thought to have had a global ocean that was lost. Most features volcanic in origin, entire surface periodically thought to erupt at once. Upper altitudes are thought to be favorable to life. Rains sulfuric acid. Visited by early Russian landers and orbiters. Orbited and mapped by Pioneer Venus and Magellan. Currently orbited by Venus Express.
Earth - Third planet from the Sun and home planet of mankind. The largest solid body in the solar system. The only known planet to currently have abundant liquid water on its surface, oceans, and life. The only planet that has active plate tectonics and volcanism and the only one with a significant proportion of its own mass.
Mars - The fourth planet orbiting the Sun. A red planet that is easily found in the night sky. It is considered to be composed of a single planetoid that did not grow due to further collisions with other planetoids due to disruptions by Jupiter. Most likely planet outside of the Earth to have once had liquid water and life and the most likely next destination for mankind. Had active volcanic and hydrological past. Has significant but thin atmosphere. Has two tiny moons which were probably captured. Has highest mountains and deepest valleys in Solar System due to its low gravity. Visited by more space probes, orbiters, landers, and rovers than any other planet. Currently being orbited by Mars Reconnaissance Orbiter and Mars Express and explored by Opportunity rover.
Jupiter - The largest and earliest formed planet in the Solar System, contains over twice as much material as the rest of the solar system combined. Influenced the formation of the other bodies in the solar system greatly. Second brightest planet in the sky and named after the king of the gods. Has four large moons and dozens of smaller ones. Upper atmosphere composed of liquid hydrogen and helium, may have a small rocky core and no solid surface. Has banded cloud features and giant long lasting storms such as the Great Red Spot. Has a powerful magnetic field. Visited by many spacecraft, orbited by Galileo. Juno probe is en route to the planet.
Saturn - Fifth planet from the Sun. The smaller of the two hydrogen/helium gas giants in the Solar System. Has large, bright, and complex ring system, which is visible in small telescopes. Has light tan banded surface, with occasional giant white storms, as well as a permanent octagon storm at the poles. Fastest spinning planet. Has one very large satellite, several smaller round ones, and dozens of irregular ones. Visited by Pioneer and Voyager spacecraft. Currently orbited by Cassini probe.
Uranus - Seventh planet from the Sun. The largest of the two Ice Giant planets in the solar system, though the least massive of the two. First new planet discovered with a telescope. Upper atmosphere composed mostly of Methane ices and is a uniform pale green atmosphere with few cloud features. Tips on its side at almost ninety degrees, experiences extreme seasonal variations. Has five small round moons and several very dark rings. Has been flown by the Voyager 2 space probe.
Neptune - Outermost planet around the Sun. More massive, yet smaller of the two Ice Giant planets. First planet predicted by its gravitational effects. Its bright blue surface caused it to be named after the god of the sea. Has many large cloud features and storms that come and go. Generates more heat than it receives from the sun. Has one large possibly captured Kuiper belt object and several smaller moons. Orbit affects the objects in the Kuiper Belt, with many of them in resonant orbits with it. Visited by the Voyager 2 spacecraft.