All four planets: Mercury, Venus, Earth and Mars are inner planets or also referred as terrestrial planets. Those are the planets orbiting closest to the Sun.
Earth is the largest of the Inner Planets, with a diameter of 12,756 km and Mercury is the smallest with a diameter of 4,878 km (3,031 miles). They have solid surfaces and thin/no atmospheres. Mercury is one of the densest planets in the Solar System. Venus is the brightest object we see in the sky, has a thick toxic atmosphere and is the hottest planet. Earth is the only planet that has liquid water.Mars surface contains iron-rich materials and has the most interesting terrain: the surface is very old and filled with craters.
