[[31.Mars is home to the highest peak in the solar system: Olympus Mons. This towering peak is 15 miles high (three times higher than Mt. Everest) and has a diameter of 375 miles (the size of Arizona). It is called a shield volcano because it has such a wide base and rises very gradually.e]]

32.The average temperature on Mars is –81° and can range from –205° in the winter to 72° Fahrenheit in the summer.

[[33.Most researchers believe that Mars’ surface was shaped by catastrophic floods billions of years ago. Scientists are unclear on what form water may have taken early in Mars’ history. One theory is that early Mars was warmer and boasted rain and oceans. Another theory is that Mars was always very cold, but water trapped underground as ice was periodically released when heating caused the ice to melt and gush to the surface. No one knows what happened to the water on Mars. Many scientists speculate that Mars’ water may have been lost into space if the atmosphere of Mars thinned out over many eons. Large quantities of water, in either ice or liquid form, are thought to be still trapped underneath its surface.e]]

[[34.In 1965, the United States spacecraft Mariner 4 made the first successful flyby of Mars. It took 228 days to reach Mars and sent 22 images to Earth. Many scientists were extremely disappointed that the images showed no signs of oceans or vegetation that they thought it would find.e In 2008, however, scientists believe they found significant evidence of carbonates in certain regions on Mars, which suggests that liquid water and perhaps even life once existed there.c]]

[[35.On November 14, 1971, the United States’ Mariner 9 was the first spacecraft to orbit Mars (or any other planet). After a massive dust storm cleared, Mariner 9 began transmitting nearly 73,000 images and revealing enormous volcanoes, huge canyons, frozen underground water in the form of permafrost, and what appeared to be dried-up river beds.b]]

36.Mars 2, built by the former Soviet Union, has the bittersweet distinction of being the first human-built object to touch down on Mars in November 1971. Unfortunately, it crashed into the surface during a massive dust storm.e

[[37.July 20, 1976, was historic because the United States’ Viking 1 was the first human spacecraft to land intact and operational on the surface of Mars. Viking 2 followed, landing successfully on September 3, 1976. The Viking Landers relayed the first color pictures of the planet. When the second Viking had its last moments of contact in 1978, project manager George Gianopoulos said “It’s like losing an old friend; how do you express it?]]

38.During the Viking missions to Mars, scientists were worried about contaminating the Martian environment with microbes from Earth.e

[[39.In 1996, the United States launched Pathfinder (also called the Sagan Lander after famed astronomer and author Carl Sagan) so that it would land on America’s Independence Day July 4, 1997. It bounced for 92 seconds on airbags before stopping, making it the first successful air bag-mediated touchdown.b]]

[[40.Pathfinder’s small robot, Sojourner, collected and studied Martian rocks. It moved less than .5 inches per second so that if it ran into trouble, scientists wearing 3-D glasses to gauge depth and perspective on their 2-D computers on Earth could send it precise directions. Sojourner was the first robot to explore another planet.b]]