Mars - Known Facts

About Mars, what scientific facts are known including trivia about the orbit, surface, and more.


Known Facts: The rotational axis of Mars is tilted with respect to its orbital plane at just about the same angle as the earth's is. This gives the red planet seasons, although they are twice as long as those on the earth because the Martian orbital period is nearly two years. Telescopic observation shows prominent white polar caps in each hemisphere becoming larger and smaller with these seasons. Changes in surface color and intensity, once thought to be growing and declining vegetation, are attributed to the redistribution of surface dust by seasonally varying winds.

The successful series of space missions to Mars, culminating in the two Viking landers in 1976, have made the planet nearly as familiar to us as the moon. The atmosphere is mostly carbon dioxide, with small quantities of nitrogen, argon, and oxygen and traces of several other gases. Total atmospheric pressure is less than 1% of the earth's, too low for water to exist as a liquid. But large amounts of water are available as ice at the Martian north pole, and there is sufficient water vapor in the atmosphere at times to form ice clouds or fog. Dust storms occur on a grand scale, occasionally blanketing the entire planet; evidence of wind erosion and sedimentation is everywhere.

Mountain ranges are virtually absent on Mars, yet there are volcanoes five times larger than any on Earth and an impressive canyon that stretches more than 2,000 mi. One hemisphere is heavily cratered and the other is mostly a vast plain, from which rise the largest volcanoes. The planet seems to be in an intermediate state of geological activity, somewhere between that of the moon, which has long been dead, and that of the earth, which is in a state of continual agitation. Analysis of surface material by the Viking landers showed large amounts of iron and silicon and significant amounts of aluminum, calcium, sulfur, and magnesium, all of which are common on Earth.

Mars has two tiny moons, both with highly cratered surfaces indicating great age and suggesting that they were captured by the planet's gravitational field as they wandered through the solar system. Phobos, orbiting less than 4,000 mi. from the planet's surface, is about 13 mi. across at its greatest dimension. Deimos is about half as large and orbits at approximately 12,000 mi.

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