Mars

Structure

Mars's Structure
Feature	% of radius
Core	38.5%
Mantle	60%
Crust	1.5%
Atmosphere	2%

The Core
Mars's core is composed mostly of liquid iron-sulfide, and contains some nickel. Its composition makes Mars's magnetic field very weak. It also makes Mars's surface gravity amazingly small because it is so light.

The Mantle
Mars's mantle is mostly molten rock silicates, possibly with some metallic oxides.

The Crust
Mars's crust is composed of mostly rock silicates; however, some grains of soil are made of iron. These rusted grains give Mars its red color. The crust seems to be split into two halves; a north half and a south half. The halves are divided by a line which crosses the Martian equator at an angle of 35°.

Ancient volcanoes litter the Martian surface, especially in the north. The largest one, Olympus Mons, is more than 330 miles (530 kilometers) in diameter. It and other dead volcanoes are about 17 miles (27 kilometers) high, 3 times higher than Mount Everest. Measurements indicate that Olympus Mons is probably about 200 million years old, but these measurements are uncertain. An age of 200 million years old would make Olympus Mons Mars's largest volcano, but it may be much older. Volcanoes exist in the southern half too, but not as many.
Impact craters are very common in the southern half, but not in the north. The southern landscape is ancient; about 4 billion years old, in fact, so it displays craters caused by the initial meteorite bombardment early in the Solar System's history. However, they are worn smooth.
Canyons on Mars are spectacular. One, Valles Marineris can be as wide as 300 miles (500 kilometers). It is long enough to span the contiguous United States.
Channels, formed by water in Mars's past, arrange themselves in intricate systems. Once full of water, they are now totally dry.
Ice caps stay constantly at Mars's poles. They are made mostly of "dry ice," or solid carbon dioxide. In the Martian summer (which, as on Earth, comes at different times for different hemispheres,) the summer pole shrinks away almost to nothing. The carbon dioxide, refusing to be a liquid, sublimes, enters the atmosphere, and freezes again at the opposite pole. When it is summer in the northen hemisphere, the tiny remaining pole is made of mostly water-ice; in the south, the summer pole is carbon dioxide ice. Nobody knows why.

The Atmosphere
Mars's atmosphere is very thin; its pressure is 1/150th of Earth's. It is so thin that one would have to go 22 miles (36 kilometers) above Earth's surface to find air pressure so weak. It is made mostly of carbon dioxide, but it also contains small amounts of nitrogen, argon, oxygen, and water vapor. Thin water ice clouds float in the Martian atmosphere at altitudes between 6 and 15 miles (10 to 25 kilometers); however, Mars's atmosphere is 100 times as dry as Earth's. Frozen carbon dioxide clouds are responsible for rare snows. Most of this gas comes from the summer ice cap. Mars's wind can blow up planetwide dust storms up to 30 miles (50 kilometers) high. These dust storms are part of the process by which Mars's craters are smoothed.

History

Mars started as a ball of molten rock. It had neither core nor crust; the materials that would make each were suspended in the liquid. Eventually, the heavier metals sank to the bottom and lighter crystals floated to the top and cooled. The solid crust was pounded by asteroids. Radioactive decay began to produce more heat. For a few billion years, the heated mantle released more lighter crystals to the top, thickening the crust. The internal heating caused Mars to expand. This expansion split the crust, forming the great Valles Marineris and other Martian canyons. It also pushed lava from the interior, forming huge volcanoes. Where lava was released, gases were also released, forming a primitive atmosphere which in density resembled Earth's present atmosphere more than Mars's. This primitive atmosphere contained lots of water vapor, which caused the greenhouse effect to take hold. It rained on Mars for millions of years. The water caused erosion of drainage channels which we still see today. When Mars entered an ice age like the one it experiences today, some water entered the ice caps and some flowed underground and permanently froze. Later, either as the result of increased volcano activity or as the result of a great meteoroid bombardment, the crust was broken and water was released in a great deluge. The floods cut deep channels into the Martian crust.
People used to think that life existed on Mars. Features like planetwide dust storms and water channels were visible through telescopes. The dust storms were once thought to be seasonal vegetation; for a time, the darker dust would engulf the planet, making people think that Martian plants were flourishing during the Martian summer, and then the dust storms would die down, revealing the Martian surface; people thought that that meant that it was winter on Mars. And when an astronomer noted channels, the dry rivers carved by water, he used the word canal, which in his language meant channel, but which people thought indicated sentient life capable of massive engineering feats. The idea of life on Mars was so accepted that when War of the Worlds was broadcast over the radio by Orson Welles, many people thought that it was a news broadcast; that Martian life was invading at that very moment and that the human race was doomed. However, life, at least life as we know it, has not been found on Mars. When the Viking landers landed on Mars, they did five different kinds of tests to determine if there was life. One test was visual; the Viking landers had cameras which were meant to confirm or disprove the existence of visible life, alive or dead. Another test used an instrument to analyze the Martian soil and determine whether there were organic molecules. The next test tested whether anything in the soil changed carbon dioxide into other chemical compounds; our plants use carbon dioxide and water to produce sugar and oxygen. The fourth test measured whether carbon dioxide or oxygen was released from the soil. The final test looked for anything in the soil that might consume chemical compounds. None of the tests found anything.

Mars Facts
		Customary	Metric
Equatorial Diameter	4,217 mi	6,787 mi	Earth is almost 90% wider than Mars
Polar Diameter	4,192 mi	6,746 km	Earth is almost 90% taller than Mars
Mean Density	3.94• water density		1 tsp of Mars weighs 71% as much as 1 tsp of Earth
Mass	1.409• 10²⁴	6.391• 10²³	Mars weighs 10.7% as much as Earth
Grav. Acceleration	12.2 ft/sec²	3.7 m/sec²	G-force on Mars is about .4 G's
Escape Velocity	3.11 mi/sec	5.01 km/sec	Can go less than half as fast to escape Mars
Number of Moons	2		Mars has 1 more moon
Distance to Sun: Average	141,500,000 mi	227,700,000 km	Mars is about 50% farther from the sun
Minimum	128,300,000 mi	206,500,000 km
Maximum	154,700,000 mi	249,000,000 km
Orbital Velocity: Average	53,980 mph	86,870 kph	Mars goes 4/5 as fast in its orbit
Minimum	49,170 mph	79,130 kph
Maximum	59,260 mph	95,370 kph
Orbital Period	686.98 Earth days		Mars's year is 90% longer
Orbital Eccentricity	.093		Earth's orbit is more of a circle
Orbital Inclination	1.8°		Mars's orbit is tilted 1.8° from Earth's
Axal Inclination	25.2°		Mars's arctic and tropical zones are about as big as Earth's
Rotational Period	24 hrs 37 min		Mars's day is about as long as Earth's
Albedo	15%		If both recieve equal light, Earth will be more than twice as bright
Surface Temperature	-194-80° F	-126-27° C	Mars's coldest 67° F (38° C) colder; hottest 56° F (31° C) cooler

Phobos and Deimos are Mars's two moons. They were not discovered until 1877. From Mars, bright Phobos moves across the sky backwards to the stars in 4 hours. It is about one-third as wide as the Moon from Earth. Deimos takes 60 hours to cross the sky, a bright dot moving in the same direction as, but slower than, its fellow bright dots the stars.

The Inner Planets
Next From the Sun: The Asteroid Belt
Next Planet: Jupiter