Mars
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Mars is the fourth planet from the Sun in the solar system, named for the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color.
Physical characteristics
Mars has always fascinated people. Its red, fiery appearance was mysterious and intriguing. Mars has only a quarter the surface area of the Earth and only 1/10th the mass (though because it lacks oceans the area of Mars's accessible 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's 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. On August 6, 1996 NASA announced that analysis of the ALH 84001 meteorite thought to have come from Mars, shows some features that may be fossils of single-celled organisms, although this idea is controversial. There is as yet no conclusive evidence that there has ever been life on Mars.
See the NASA Mars Fact Sheet, Mars' size compared to Earth
Topography
Zero elevation. Since Mars has no oceans, thus no 'sea level' a zero-elevation surface or mean gravity surface must be selected.
Zero meridian. Mars' 'equator' needs to be accurately established for mapping. A crater in the Sinus Meridiani ('Equatorial Gulf') has been arbitrarily selected to represent zero meridian.
Some basic features of Martian topography. Mars has polar ice caps that contain frozen water and carbon dioxide. An extinct shield volcano, Olympus Mons ('Mount Olympus'), is at 27 km the tallest mountain in the solar system. It is in a vast upland region called Tharsis, containing several large volcanos. Mars also has the solar system's largest canyon system, Valles Marineris or the scar of Mars, which is 4000 km long and 7 km deep.
The dichotomy of Martian topography is striking: northern plains flattened by lava flows and the southern highlands, pitted and cratered by ancient impacts. The surface of Mars as seen from Earth is consequently divided into two kinds of areas, with differing albedo. The paler plains covered with dust and sand rich in reddish iron oxides were once thought of as Martian 'continents' and given names like Arabia Terra ('land of Arabia') or Amazonis Planitia ('Amazonian basin'). The dark features were thought to be seas, hence their names Mare Erytherium, Mare Sirenum and Aurorae Sinus. The largest dark feature seen from Earth is Syrtis Major.
The largest impact crater on Mars is the Hellas impact basin, covered with light red sand.
The International Astronomical Union's Working Group for Planetary System Nomenclature is responsible for naming Martian surface features.
See also the list of mountains on Mars and list of craters on Mars.
Mars's moons
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's surface. Deimos, on the other hand, is far enough away that its orbit is being slowly boosted instead.
Both satellites were discovered in 1877 by Asaph Hall, and are named after the characters Phobos and Deimos in Greek mythology, sons of the Greek god Ares.
| Name | Diameter (km) | Mass (kg) | Mean orbital radius (km) |
Orbital period |
|---|---|---|---|---|
| Phobos | 22.2 (27 × 21.6 × 18.8) | 1.08×1016 | 9378 | 7.66 hours |
| Deimos | 12.6 (10 × 12 × 16) | 2×1015 | 23,400 | 30.35 hours |
The exploration of Mars
Unmanned probes
Many robotic probes have been sent from Earth to Mars, with a few spectacular successes and a notably high failure rate. Some of the failures can be ascribed to technical incompetence, but enough others have failed for no apparent reason for researchers to half-jokingly speak of an Earth-Mars "Bermuda Triangle" or of a Great Galactic Ghoul which subsists on a diet of Mars probes. In order to understand the history of the robotic exploration of Mars it is important to note that launch windows occur at intervals of slightly over 2 years (the planet's synodic period).
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. 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.
NASA continued the Mariner program with another pair of Mars flyby probes at the next launch window. These probes reached the planet in 1969. See Mariner 6 and 7 for details. During the following launch window the Mariner program again suffered the loss of one of a pair of probes. Mariner 9 successfully entered orbit about Mars, after the launch time failure of its sister ship, Mariner 8. When Mariner 9 reached Mars, it and two Soviet orbiters, found that a planet-wide dust storm was in progress. The mission controllers used the time spent waiting for the storm to clear to have the probe rendezvous with, and photograph, Phobos. When the storm cleared sufficiently for Mars' surface to be photographed by Mariner 9, the pictures returned represented a substantial advance over previous missions. These pictures were the first to offer evidence that liquid water might at one time have flowed on the planetary surface.
In 1976 the two Viking probes entered orbit about Mars and each released a lander module that made a successful soft landing on the planet's surface. These missions returned the first color pictures and extensive new scientific information.
The Soviet probes of the Mars probe program attempted a number of landings several years before Viking, but were not nearly as successful as the Martian missions of the Mariner program. The later Soviet Phobos 1 and 2 probes were similarly unsuccessful.
The Mars Pathfinder spacecraft, landing on July 4, 1997, carried a tiny remote-controlled rover called Sojourner, which travelled a few metres around the landing site, exploring the conditions and sampling rocks around it. The mission website was the most heavily-trafficked up to that time.
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 scientific 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's north polar ice cap.
Recent findings by the Mars Odyssey probe's gamma ray spectrometer and neutron spectrometer have determined that there are vast deposits of water ice in the upper three meters of Mars's soil within 60° latitude of the south pole. Similar quantities of ice are expected to be present in the north polar region as well, but measurements will not be made until later in 2002.
On June 2, 2003, the European probe Mars Express set off from Baikonur Cosmodrome to the Mars. Although the landing probe will not move, it carries a digging device and possibly the smallest mass spectrometer, as well as a range of other devices, on a robotic 'arm' in order to accurately analyse soil beneath the dusty surface. The Mars Express craft consists of the Mars Express Orbiter and the lander Beagle 2. The orbiter entered Mars orbit on December 25, 2003, and Beagle 2 entered Mars' atmosphere the same day. Initial attempts to contact the lander failed.
On June 10, 2003, NASA's MER-A ("Spirit") Mars Exploration Rover was launched. On January 4, 2004 it landed in an area called "Gusev Crater" (believed to once being a crater lake). It will examine rock and soil for evidence of the area's history of water. On July 7, 2003, a second rover, MER-B ("Opportunity") was launched. It is planned to land on January 25, 2004 in an area called "Meridiani Planum" and will carry similar geological work. The two names for these rovers were chosen by looking at essays from kids around the U.S.
Several other recent probes from the United States and Russia have failed upon arrival at Mars.
Manned missions
Many people, from Wernher Von Braun on, have long advocated a manned mission to Mars as the next logical step for a manned space program. As well as the undeniable romanticism of human exploration, such advocates believe that the amount of scientific work able to be performed in a human mission would be far superior than that possible with robotic explorers, thus making the large cost of a manned mission justifiable. With present technology, Mars Direct, forcefully advocated by Robert Zubrin of the Mars Society, is believed by many as the most practical and affordable plan for a manned Mars mission.
ESA, the European Space Agency, plans to visit Mars by 2030.
Longer term, some scientists believe Mars to be a good candidate for terraforming and human colonization, though other prominent skeptics (such as Robert Park) hotly dispute its practicality.
This image was acquired at the Viking Lander 1 site with camera number 1. The large rock just left of center is about 2 meters wide. This rock was named "Big Joe" by the Viking scientists. The top of the rock is covered with red soil. Those portions of the rock not covered are similar in color to basaltic rocks on Earth. Therefore, this may be a fragment of a lava flow that was ejected by an impact crater. (Larger image)
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The "Ares Vallis" area, which is among the rockiest parts of Mars, as photographed by the Mars Pathfinder lander in its 1997 mission. The "twin peaks" are seen in the distance. (Larger image)
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Mars with caps
Miscellaneous
Earth passes Mars every 26 months at a distance of about 80 000 000 km. However, this varies because the orbits are elliptic.
On August 27, 2003, at 9:51 UTC, Mars made its closest approach to Earth in nearly 60,000 years: approximately 34,646,416 miles (55,758,000 kilometers). This close approach while in opposition made Mars particularly easy to see from Earth. The last time it came so close is estimated to be in 57,617 BC. Detailed analysis of the solar system's gravitational landscape forecasts an even closer approach in 2287.
A handful of objects are known that are surely meteorites and may be of Martian origin. Two of them may show signs of ancient bacterial activity.
See also
- "The Political Economy of Very Large Space Projects" at Journal Of Evolution and Technology
- Mars in fiction
- Darian calendar
External link
The Solar System
Sun - Mercury - Venus - Earth - Mars - Asteroids - Jupiter - Saturn - Uranus - Neptune - Pluto - Comets - Kuiper belt - Oort cloud