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Observing the Sky Solar System Satellites Navy Research Resources

Solar System: Inner Planets - Mars

The Red Planet

Mars, the fourth planet from the Sun, is the last of the inner, terrestrial planets. Its surface is covered with an iron-rich clay, giving the planet a reddish color. Even with the unaided eye, Mars appears redder than the other planets and stars in the night sky. Mars has two moons: Phobos, which is about 13 miles wide, and Deimos, which is about 7 miles wide. These moons are so small that some scientists believe they are asteroids that were captured by Mars’s gravitational field.

Photo of Mars
Courtesy of NASA JPL

When spacecraft began photographing Mars in the 1960s and 1970s, astronomers didn’t find the Martian people that many science fiction writers had predicted. They did find mountains that are three times higher than Mount Everest, a canyon that is as long as the United States is wide, a bulge that is bigger than Alaska and over six miles high, and a crater that is almost four miles deep. Images have also shown signs of erosion in many places, indicating that Mars may have had flowing rivers or oceans in the distant past.

In 1997, the Mars Pathfinder landed on the planet surface, and sent the rover Sojourner to study the area around its landing site. The mission proved that relatively low-cost missions to Mars were possible, and provided a great deal of information on the geology, chemistry, and atmospherics of the planet.

In early 2004, the Spirit and Opportunity rovers landed in two different locations on the surface of Mars. Like robotic geologists, Spirit and Opportunity are currently exploring the Martian surface, taking samples of the soil and rocks and sending back many incredible images. The Odyssey and Mars Global Surveyor continue to orbit the planet, studying its geology, weather, and climate from above. They also perform an important role in the rover missions, relaying commands from Earth to the rovers, and data from the rovers to Earth.

Mars is in the evening sky through winter and spring in 2004, in Taurus, setting at sunset by June. Look for the red planet in the eastern morning sky beginning in mid-October and through the end of the year.