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| Quick Facts
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Mass : 6.42 x 10^23 kg
Diameter : 6787 km
Mean density : 3940 kg/m^3
Escape velocity : 5000 m/sec
Average distance from the Sun : 227,940,000 km
Average distance from Sun : 1.524 AU
Rotation period/Length of day : 1.026 Earth days
Revolution period/Length of year : 686.98 Earth years
Obliquity/Tilt of axis : 25 degrees
Orbit inclination : 1.85 degrees
Orbit eccentricity/deviation from circular : 0.093
Maximum surface temperature : 310 K
Minimum surface temperature : 150 K
Visual geometric albedo (reflectivity) : 0.15
Magnitude : -2.01 Vo
Highest point on surface: Olympus Mons, 24 km high
Atmospheric components: 95% carbon dioxide, 3% nitrogen, 1.6% argon
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| The Red Planet
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Mars is the fourth planet from the Sun ( approximately 227,940,000 km or 1.52 AU away from the sun) and is commonly referred to as the Red Planet. The rocks, soil and sky have a red or pink hue. The distinct red color was observed by stargazers throughout history. It was given its name by the Romans in honor of their god of war.
Mars' orbit is significantly elliptical. One result of this is a temperature variation of about 30 C at the subsolar point between aphelion and perihelion. This has a major influence on Marsą climate. While the average temperature on Mars is about 218 K (-55 C, -67 F), Martian surface temperatures range widely from as little as 140 K (-133 C, -207 F) at the winter pole to almost 300 K (27 C, 80 F) on the dayside during summer.
Although Mars is smaller and colder than Earth, it is still quite similar to our planet. It has a thin atmosphere and polar ice caps, and dry riverbeds crisscross its surface (this will be elaborated further later in the page). And frozen or even liquid water may exist beneath the red Martian soil -- perhaps providing a home for living organisms. But it is not the planet described in science-fiction books and movies. There are no signs of civilizations on its surface -- past or present.
Presently, Martian atmosphere is less than 1% as thick as our atmosphere. However, it is possible that Mars once had an atmosphere somewhat like Earth's, and almost certain that water once covered part of the Martian surface. Features resembling gorges, riverbeds, islands, shorelines have been found, suggesting that great rivers once flowed on the Martian surface. Although no water is found in the Martian canals today, frost covers the north and south poles. These polar ice caps are made mostly of frozen carbon dioxide (dry ice) and some ice water too.
From the Earth, Mars is easily seen in the night sky as a red star-like object that moves through the sky with a period of just over two years. As the orbit of Mars is an eccentric ellipse its distance from the Earth at opposition (closest approach to the Earth) varies between 1.38 and 1.67 Astronomical Units (the mean distance of the Earth from the Sun is one Astronomical Unit). Seen through a telescope Mars appears as a small reddish disk on whose surface dark markings can (with difficulty) be seen. Also visible is one or other of its polar caps.
| Life on Mars?
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Before space exploration, Mars was considered the best candidate for harboring extraterrestrial life. Astronomers thought they saw straight lines crisscrossing its surface. This led to the popular belief that irrigation canals on the planet had been constructed by intelligent beings.
Another reason for scientists to expect life on Mars had to do with the apparent seasonal color changes on the planet's surface. This phenomenon led to speculation that conditions might support a bloom of Martian vegetation during the warmer months and cause plant life to become dormant during colder periods.
In July and September 1976, Viking Landers 1 and 2 touched down on the surface of Mars. The three biology experiments aboard the landers discovered unexpected and enigmatic chemical activity in the Martian soil, but provided no clear evidence for the presence of living microorganisms in the soil near the landing sites. According to mission biologists, Mars is self-sterilizing. They believe the combination of solar ultraviolet radiation that saturates the surface, the extreme dryness of the soil and the oxidizing nature of the soil chemistry prevent the formation of living organisms in the Martian soil. The question of life on Mars at some time in the distant past remains open.
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