Mars is a cold, dry, desert landscape of sand and rocks. Many land features on the present-day surface of Mars, such as volcanoes, canyons, and valleys, make it look very similar to Earth, but humans could not survive in the present environment on Mars. The average surface temperature is -63 degrees C (-81 degrees F), and nighttime temperatures on Mars can plunge to -110 degrees C (-170 degrees F). By comparison, the lowest temperature ever recorded on Earth was -89 degrees C (-130 degrees F) at Vostok, Antarctica in July, 1983.
Surface Features and Geology
Mars is only about one-half the diameter of Earth, but both planets have roughly the same amount of dry land surface area. This is because over two-thirds of the Earth's surface is covered by oceans, whereas the present surface of Mars has no liquid water.
Although Mars and Earth are very different planets when it comes to temperature, size, and atmosphere, geologic processes on the two planets are surprisingly similar. On Mars, we see volcanoes, channels, and impact basins much like the ones we see on Earth. Because of this similarity, scientists can study certain geologic features and processes on Earth in order to learn about the same or similar features on Mars. These comparisons are called analogs. Because we don't yet have the capability to send humans to do fieldwork on Mars, these Mars/Earth analogs enable scientists to make inferences about features they see on Mars by combining field studies on Earth with satellite imagery of the Martian surface, as well as imagery obtained by landers.
This global image of Mars was taken by the Wide-Field Planetary Camera 2 on the Hubble Space Telescope. The north polar cap can be seen at the top, and the immense rift valley called Valles Marineris is visible in the lower left. (Image Credit: Philip James, University of Toledo; Steven Lee, University of Colorado; and NASA)
Because of the similar geologic processes, many of the same physical land features we see on Earth also exist on Mars. But the sheer size of some landforms on Mars dwarfs that of similar features on Earth. For example, Olympus Mons is not only the largest volcano on Mars, it's the largest known volcano in the solar system. Towering at 26 km (16 miles) high, Olympus Mons is about four times as tall as Mauna Loa, the largest volcano on Earth, and about three times as high as Mount Everest. Mars also boasts a canyon system that would extend all the way across the United States, if on Earth. Valles Marineris, sometimes called the Grand Canyon of Mars, is 7 km (4.3 miles) deep and 4000 km (2500 miles) long, which is actually ten times longer and about four times deeper than the Grand Canyon.
Mars is a desert landscape of sand and rocks. This false-color image was taken in November 2005 by Rover Spirit's panoramic camera near an outcrop called "Seminole." (Image Credit: NASA/JPL-Caltech/Cornell)
Located on the Big Island of Hawaii, Mauna Loa is the largest volcano on Earth. Mauna Loa's summit caldera has gases and steam rising from fumaroles along a fissure that erupted in July 1975. The caldera is about 3 km (1.8 miles) wide. (Image Credit: R.B. Moore, USGS)
The Martian surface is also covered with many impact craters -- a remnant of the time in the planet's geologic history when it was heavily bombarded by planetary debris. Since an older planetary surface will have more impact craters than a young surface, scientists are able to deduce the age of various regions on the Martian surface by studying the distribution of impact craters.