Mars is called the "red planet" because of the iron-oxide dust that gives it the red colour. The fourth planet from the sun is a cold world, as you might expect, with the only "water" so far discovered in the form of ice at the poles.
Mars is roughly half the size of the Earth. It has a diameter of 4,222 miles, compared to Earth's 7,962 miles at the equator. Mars is 53% as large as Earth; this means that Mars has a gravity that is less than 40% of what people feel on Earth. Mars has an atmosphere, but it is less than one per cent of Earth's and is comprised mostly of carbon dioxide.
Since it is a relatively close neighbour, Mars has been studied extensively. The largest mountain discovered in the solar system so far lies on Mars, the 78,000-foot-tall Olympus Mons. Compare this mountain to the highest on Earth, Mount Everest, and you will see that Olympus Mons is nearly three times as high.
It takes Mars a bit more than 686 earth days to make its orbit around the sun. Mars is approximately 230 million miles from the sun; in comparison the Earth is 93 million miles distant. A Martian day is just a little longer than one on Earth, lasting 24 hours and 39-and-a-half minutes. The tilt of its axis means that Mars also experiences seasons like Earth does, but they are twice as long due to the length of the year on Mars.
Mars has recently been found to have an impact crater on it that is three to four times larger than any found on Earth. It is called an impact crater because it was caused by a meteor or asteroid hitting the ground. Scientists theorise that some four billion years ago, an object perhaps a fraction of the size of our moon collided with the northern hemisphere of Mars. The resulting crater that now exists is equal in size to the combined land area of the continents of Europe, Asia and Australia.
Mars has other features that are much bigger in comparison to Earth's. Consider the Valles Marineris, a huge canyon discovered on Mars. It spans a length of 4,000 kilometres and is 7 kilometres deep. This means that this single canyon is longer than the length of Europe and goes for one-fifth the circumference of the entire planet. Compare this canyon to Earth's Grand Canyon and you will see that it dwarfs it in size. The Grand Canyon is "only" 446 kilometres long and 2 kilometres deep. Another canyon on Mars, Ma'adim Vallis, is larger than the Grand Canyon at 700 kilometres long and 2 kilometres deep.