National Geographic News
In the late 19th century the U.S. astronomer Percival Lowell popularized the notion that Mars was home to visible canals. He believed that a race of intelligent Martians created canals to transport water from polar ice caps to the rest of their drying, dying planet.
Lowell's theory of a Martian Venice didn't hold water, but it does remind us just how much scientists have learned about the red planet since thenand how much remains to be discovered today.
To that end, in 2003 NASA separately sent two roving, robotic geologists, Spirit and Opportunity, to explore the red planet. The rovers have collected a trove of scientific data, and yesterday Spirit marked the one-year anniversary of its Martian exploration.
To mark the occasion, National Geographic News has compiled some often surprising facts about our celestial neighbor:
The Romans named Mars after their god of war. The planet has two moonsPhobos (Greek for "fear") and Deimos (Greek for "panic"). The moons are named for the horses that pulled the chariot of Ares, the Greek god of war.
Many scientists believe that Phobos and Deimos are in fact captured asteroidsasteroids that flew into Mars's orbit and never quite shook free.
Italian astronomer, mathematician, and physicist Galileo Galilei made the first telescopic observation of Mars in 1609.
Humans may one day visit Mars, but getting spacecraft there is a difficult feat. Among all international unmanned missions to Mars, some two-thirds have failed to reach the red planet.
A Martian day is nearly the same length as an Earth day24 hours and 37 minutes. The Martian year, however, lasts nearly twice as long one of ours, spanning 687 Earth days.
Martian volcanoes are ten to a hundred times larger than their Earthly counterparts. Olympus Mons, the solar system's largest volcano, covers about the same area as Arizona. This Martian shield volcano sprawls some 374 miles (624 kilometers) in diameter and towers 16 miles (25 kilometers) high.
Valles Marineris, or Mariner Valley, is an enormous Martian canyon system nearly as long as the continental United States. The 2,500-mile-long (4,000-kilometer-long) system reaches depths of up to 4 miles (7 kilometers) and stretches along one-fifth of the Martian equator. The canyon was likely caused by tectonic "cracking" of the red planet's crust.
Visible from Earth through a good telescope, the northern and southern polar ice caps of Mars are made from dry ice (solid-state carbon dioxide). Scientists debate how much water ice the polar caps may also contain. Layers within the ice caps could someday reveal clues to Mars's climactic history.
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