There are 8 planets in our solar system. The first four are Mercury, Venus, Earth, and Mars. These are called the terrestrial planets because they all have a core surrounded by rock like Earth. Also like Earth, the mantle and crust of these planets contains numerous silicates (silicon oxygen compounds) and minerals like Earth's rocks. Mars, in particular, is covered in iron oxide (rust) which gives it its distinctive red color. The other 4 planets are Jupiter, Saturn, Uranus, and Neptune. These are called the gas giants since they are predominantly made up of gas. Specifically, Jupiter and Saturn are composed of a core surrounded by gases hydrogen and helium. Uranus and Neptune are sometimes called the ice giants since they also have not only hydrogen and helium but also flozen ice particles of heavier chemicals like water, ammonia, and methane. But all of the gas giants don't have rocky surfaces like Earth so a spacecraft could never "land" there. Also remember that Pluto is no longer technically considered a planet (it is classified as a dwarf planet).