The scale of the planets in our solar system is difficult to grasp without visual aid. The planets come in roughly two main types, the terrestrial or rocky planets (Mercury, Venus, Earth, Mars) and the gas giants (Jupiter, Saturn, Uranus, and Neptune. Since 2006 a third category, dwarf planets has been added with includes Pluto and the asteroid Ceres. In addition there are numerous moons, some of which are larger than the planet Mercury (Jupiter’s moon Ganymede and Saturn’s moon Titan.)
Of the terrestrial planets, Earth is the largest with a diameter of just under 8,000 miles. Venus is slightly smaller at approximately 7,500 miles in diameter, Mars is next at 4,200 miles in diameter and Mercury comes in at just over 3,000 miles in diameter. All of the terrestrial planets are small compared to the gas giants.
The gas giants are composed of gases with no surface on which to stand on. Jupiter is the largest gas giant with an almost 89,000 mile diameter, eleven times the diameter of Earth. The Great Red Spot of Jupiter which is storm that has raged for at least 300 years is larger than the entire planet Earth! Saturn is the second largest planet with a diameter of just under 75,000 miles but it’s rings are 170,000 miles in diameter and are composed of ice with a bit of rock. Uranus is next at just under 32,000 miles and Neptune is the fourth largest planet at just under 31,000 miles in diameter, so both are about four times the diameter of Earth.
The dwarf planets are all smaller than Earth’s moon and currently Eris is thought to be the largest with a diameter of 1,450 miles. This compares with Pluto’s diameter of about 1,400 miles so they are very similar.
The Sun makes all of the planets look small with its diameter of just under 850,000 miles or over 100 times as wide as the Earth!
One of the best ways to help visualize the scale of the planets is to see images of the planets proportionally scaled. There are websites on the internet that do this with great images of all the planets. Another great place to find to see this is at the website of Proportional Planets which actually sells a product consisting of proportionally sized, high quality, cut-out images of the planets. It is amazing to hold the image of the Earth up to the other planets to really get a feel for the various sizes.