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How Long Is One Mars Day?

The planet Mars has long been a source of speculation and awe for people on Earth, and no wonder: at various times during the Earth year, the red planet is clearly visible, glowing brightly in the sky. We let our imaginations run wild over it--the planet has inspired such films as "The War of the Worlds," "Mars Needs Women" and "Mars Attacks." We can imagine all sorts of fantastic things about Mars, and it turns out, the truth is even more interesting. Science has given us plenty of cool facts about Mars, including the duration of one Mars day.

Time Frame
- Earth rotates on its axis once every 24 hours; one Earth day. Mars takes 39 minutes longer than Earth to rotate on its axis; scientists call this passage of time (24 hours and 39 minutes) a Sol--a martian solar day.
Features
- Two tiny, oddly shaped moons, Phobos and Deimos, orbit Mars. Phobos, the larger and closer of the two, circles Mars once every 7.3 hours, which creates an unusual illusion: Phobos appears to rise in the West and set in the East. For comparison, our Moon makes one complete orbit around the Earth in just over 27 days. Scientists believe that Phobos and Deimos are more like asteroids than they are like Mars.
Considerations
- Mars experiences seasons similar to those on Earth. The climate, however, is much colder. Because the planet is farther from the Sun, low temperatures on Mars reach -220 F (-140 C). Scientists are studying the giant dust storms that occur during the southern spring and summer, sometimes covering the planet, to learn more about the planet's climate patterns.
Geography
- Mars is the fourth planet from the sun. It makes an elliptical orbit around the Sun; at its closest, it comes within 128 million miles of the Sun. At its farthest, it is 155 million miles distant. The Red Planet takes 687 Earth days to complete its orbit, making a year on Mars almost twice the length of a year on Earth.
History
- Scientists disagree over the age of the Martian surface. They count the craters on the planet's surface to get an estimate of 4.6 billion years; in comparison, Earth is estimated to be 4.5 billion years old. Roughly one-half the size of Earth, Mars comes within 35 million miles of Earth during the two planets' orbits.
Expert Insight
- Exploration of Mars is teaching us more and more. In 2003, NASA sent two rovers on their way to Mars; after a six-month journey, they landed in January 2004, and began sending images of the planet almost immediately. Scientists are collecting a huge volume of information and data from the rovers' travels across the planet's surface. Most recently, NASA orbiters used ground-penetrating radar to reveal the presence of massive underground glaciers on Mars. The discovery suggests an ice age on Mars similar to those on Earth.

Astronomy