Mars is the fourth planet in the solar system, named for the Roman god of war (the counterpart of the Greek Ares), on account of its red color. Mars has always fascinated people. Its red, fiery appearance was mysterious and intriguing. Mars has only a quarter the surface area of Earth and only 1/10th the mass (though because it lacks oceans the area of Mars' accessable dry land is approximately equal to that of the Earth's dry land). Mars has two small moons, Phobos and Deimos, both small and oddly shaped, possibly captured asteroids. Mars has polar ice caps that contain frozen water and carbon dioxide. An extinct volcano, Olympus Mons, is, at 25 km, the tallest mountain in the solar system. Mars' atmosphere is very thin, the surface air pressure is only 7.5 millibars compared to an average 1013 millibars on Earth. The atmosphere on Mars is 95% carbon dioxide, 3% nitrogen, 1.6% argon, with only a trace of oxygen and water.
Mars has an important place in human imagination due to the old belief that life existed on Mars. This was supposed because of observations of linear features on the surface that appeared artificial and seasonal changes in the brightness of some areas that were thought to be caused by vegetation growth. This gave rise to many stories concerning Martians. The linear features are now know to be non-existent or in some cases, ancient dry watercourses. The color changes have been ascribed to dust storms. Recently analysis of meteorites thought to have come from Mars show some features that may be fossils of single celled organisms.
- equatorial diameter: 4,212.28 miles (6,794 kilometers)
- mass: 6.4191×1023 kg (0.11 of the Earth)
- mean relative density: 3.95
- surface gravity: 0.38
- surface area relative to Earth: 0.28 (144 million km2)
- farthest distance from the Sun: 154,900,000 miles (249,200,000 kilometers)
- closest approach to earth approx.: 48,700,000 miles (78,390,000 kilometers)
- orbital period: 687 earth days
- rotational period: 24hrs. 37mins.
- low temperature: -305 F (-187 C)
- satellites : 2, Phobos (from Greek Fear) and Deimos (from Greek Panic)
Mars's natural satellites
- Orbital radius: 9378 km (note: measured from the center of Mars)
- Diameter: 22.2 km (27 x 21.6 x 18.8)
- Mass: 1.08×1016kg
- Orbital period: 0.31910 days (7.66 hours)
- Rotational period: 0.31910 days (7.66 hours)
- Density: 2.0 g/cm3
- Orbital inclination: 1.0°
- Orbital radius: 23,400 km
- Mass: 2×1015 kg
- Rotational period: 30.35 hours
- Orbital period: 30.35 hours
- Dimensions: 10 km X 12 km X 16 km
Both Phobos and Deimos are tidally locked with Mars, always pointing the same face towards it. Since Phobos orbits around Mars faster than the planet itself rotates, tidal forces are slowly but steadily decreasing its orbital radius. At some point in the future Phobos will impact on Mars' surface. Deimos, on the other hand, is far enough away that its orbit is being slowly boosted instead.
The history of Mars exploration is riddled with failures, disappointments, and gross incompetance. The quest for more information about the Red Planet still draws the attention of some of the best scientific minds available.
Two Soviet flyby probes were launched towards Mars in October 1960 but failed to reach Earth orbit. In 1962, three more Soviet probes failed -- two remaining in Earth orbit and one losing communication with Earth en route to Mars. In 1964, there was another failed attempt to reach Mars.
Between 1962 and 1973, NASA's Jet Propulsion Laboratory designed and built 10 spacecraft named Mariner to explore the inner solar system. These spacecraft were designed to visit the planets Venus, Mars and Mercury for the first time. They would then return to Mars for additional close observations. The Mariners, relatively small robotic explorers, were launched on Atlas rockets. Each weighed less than half a ton.
Mariner 3 and Mariner 4 were identical spacecraft designed to carry out the first flybys of Mars. Mariner 3 was launched on November 5, 1964, but the shroud encasing the spacecraft atop its rocket failed to open properly. Mariner 3 failed to reach Mars. Three weeks later, on November 28, 1964, Mariner 4 was launched successfully on an eight-month voyage to the red planet.
Mariner 4 flew past Mars on July 14, 1965, providing the first close-up photographs of another planet. The pictures, played back from a small tape recorder over a long period, showed lunar-type impact craters. Some of them seemed touched with frost in the chill Martian evening.
In the 1970s the Viking probes orbited and landed on Mars, returning the first color pictures and extensive new scientific information. The Soviet probes of the Mars program attempted a number of landings several years before Viking, but were not nearly as successful.
Next came Mars Global Surveyor. This mission was the first successful one to the red planet in two decades when it launched November 7, 1996, and entered orbit on September 12, 1997. After a year and a half trimming its orbit from a looping ellipse to a circular track around the planet, the spacecraft began its primary mapping mission in March 1999. It has observed the planet from a low-altitude, nearly polar orbit over the course of one complete Martian year, the equivalent of nearly two Earth years. Mars Global Surveyor recently completed its primary mission on January 31, 2001, and is now in an extended mission phase.
The mission has studied the entire Martian surface, atmosphere, and interior, and has returned more data about the red planet than all other Mars missions combined. This valuable data is archived at http://wufs.wustl.edu/missions/mgs/mola/ .
Among key science findings so far, Global Surveyor has taken pictures of gullies and debris flow features that suggest there may be current sources of liquid water, similar to an aquifer, at or near the surface of the planet. Magnetometer readings show that the planet's magnetic field is not globally generated in the planet's core, but is localized in particular areas of the crust. New temperature data and closeup images of the Martian moon Phobos show its surface is composed of powdery material at least 1 meter (3 feet) thick, caused by millions of years of meteoroid impacts. Data from the spacecraft's laser altimeter have given scientists their first 3-D views of Mars' north polar ice cap.
Mars appears to be the best candidate today for terraforming and human colonization.