Mars is the second smallest planet in the solar system, with a diameter of just over 4,212 miles and a circumference of 13,256 miles. Its diameter is about 53 percent that of the Earth. Among the major planets, only Mercury is smaller.
Among the planets, Mars is the one most like Earth. It is a rocky planet, with a thin atmosphere and polar ice caps. Its orbital tilt produces a cycle of seasons not unlike Earth's. During Mars' summer, temperatures at the equator can reach as high as 95 degrees Fahrenheit, though on average, the temperature on Mars is far colder than on Earth. At the polar ice caps, temperatures can reach as low as -225 degrees Fahrenheit.