Mars is the fourth planet from the Sun in our solar system. Its diameter is about half that of Earth, and its year is about 687 Earth days. That means that its seasons are about twice as long as ours here on Earth. However, a Martian day is very close in length to an Earth day—only about twenty minutes longer, in fact.

The Martian atmosphere is very thin—only about seven-thousandths the density of Earth’s atmosphere. The atmosphere is mostly carbon dioxide, with tiny fractions of oxygen, nitrogen, and other gases. At the equator, during the warmest times of the Martian summer, the temperature can reach nearly zero degrees Fahrenheit (–18 degrees Celsius); at the poles, during the coldest times of the Martian winter, temperatures drop to 120 degrees below zero Fahrenheit (–85 degrees Celsius) and beyond.

Mars has fascinating geologic features on its surface; it is covered with all sorts of mountains, craters, channels, canyons, highlands, lowlands, and even polar ice caps. Scientific evidence strongly suggests that once, billions of years ago, Mars was much warmer than it is now, and was an active, dynamic planet.