The Inner Planets What Are the Inner Planets? The four planets closest to the Sun, Mercury, Venus, Earth and Mars, are grouped together as the inner planets. They have rocky surfaces, and are often called the terrestrial planets. These planets are small and closely spaced, as compared to the outer planets. Diameter (km) Distance from sun (average) Rotation (Earth Days) Revolution (Earth Days) Number of moons 4,880 km 58,000,000 km 59 88 0 Diameter (km) Distance from sun (average) Rotation (Earth Days) Revolution (Earth Days) Number of moons 12,100 km 108,000,000 km 243 225 0 retrograde rotation Mercury Mercury is the smallest planet, located closest to the Sun. It revolves on its axis very slowly. A single Mercury day is about 59 Earth days long. Mercury does not have any moons or atmosphere. Its surface is covered with craters. A magnetic field suggests that it has an iron core. Mars Mars, the fourth planet from the Sun, has two moons. A day on Mars is slightly longer than a day on Earth. Mars has a very thin atmosphere composed primarily of carbon dioxide. The surface is cold, dry, and dusty, with frozen ice caps found at its poles. Landforms and NASA rover samples indicate that there were once large amounts of liquid water on the surface of Mars. It has a volcanic history, and the largest volcano in the solar system, Olympus Mons, is found there. Earth Earth is the third planet from the Sun. Earth’s distance from the Sun allows for moderate temperatures that keep most surface water in liquid form. The presence of liquid water and an oxygen-rich atmosphere make Earth suitable for millions of living organisms. Diameter (km) Distance from sun (average) Rotation (Earth Days) Revolution (Earth Days) Number of moons 12,742 km 150,000,000 km 1 365 1/4 1 Diameter (km) Distance from Sun (average) Rotation (Earth Days) Revolution (Earth Days) Number of moons 6,780 km 228,000,000 km 1.03 687 2 polar ice cap Olympus Mons Venus Venus is the second closest planet to the Sun. It is often called Earth’s sister or twin planet due to similar composition, gravity and size. Venus rotates very slowly in a clockwise direction, called retrograde rotation. Venus does not have any moons. Venus is surrounded by a very dense atmosphere. Due to the greenhouse effect, it has the hottest surface temperature of any planet. The air pressure on Venus is 92 times that on Earth. Craters and active volcanoes cover the surface of the planet. From a geologic perspective, Venus is considered a young planet. © Copyright NewPath Learning. All Rights Reserved. 94-4581 Visit www.newpathlearning.com for Online Learning Resources. Photos courtesy of NASA, USFWS & NOAA. inner planets Mercury Venus Earth Mars
Pause and Review Fill in the table below with information about the four inner planets. The Inner Planets Distance from Sun Rotation Planet Revolution # of Moons Atmosphere/ Surface Mercury Venus Mars Earth © Copyright NewPath Learning. All Rights Reserved. 94-4581 Visit www.newpathlearning.com for Online Learning Resources.