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Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. Mars has two small moons, Phobos and Deimos, both small and oddly shaped, possibly captured asteroids.
Physical characteristics
Mars has always fascinated people. Its red, fiery appearance is 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' accessible dry land is approximately equal to that of the Earth's dry land). Mars'
atmosphere is very thin: the surface air pressure
is only 750 Pa (about 0.75% of the average on Earth). The atmosphere on Mars is 95% carbon dioxide, 3% nitrogen, 1.6% argon, with only a trace of oxygen and water. In 2003
methane was also discovered in the atmosphere by Earth-based telescopes, confirmed in March 2004 by the Mars Express
Orbiter. The presence of methane is intriguing, since as an unstable gas it indicates that there must be (or have been within
the last few hundred years) a source of the gas on the planet. Volcanic activity,
comet impact, and the existence of life in the form of microorganisms such as methanogens are among possible
but as yet unproven sources.
Mars has an important place in human imagination due to the belief by some that life existed on Mars, due mainly to
observations by Percival Lowell of Martian canals, apparently artificial linear features on the surface that he asserted were canals, and
due to 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 known
to be mostly non-existent or, in some cases, dry ancient watercourses. The color changes have been ascribed to dust storms.
In 2000, researchers studying meteorites which originated from Mars reported features which they attributed to microfossils
left by life on Mars. As of 2004, this interpretation remains controversial with no consensus having emerged.
See an image comparison: Mars' size compared to Earth
Topography
The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with 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.
North Polar region w/icecap. (Courtesy NASA/JPL-Caltech.)
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. See list of mountains on Mars. 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.
Mars is also scarred by a number of impact craters. The largest of these is the
Hellas impact
basin, covered with light red sand. See list of
craters on Mars.
The International Astronomical
Union's Working Group for Planetary System Nomenclature is responsible for naming
Martian surface features.
Other notes:
Zero elevation: Since Mars has no oceans and hence no 'sea level', a zero-elevation surface or mean gravity surface must
be selected. The "datum" was chosen to conform to a line where the atmospheric pressure is 610 Pa (6.1 mbar), approximately 0.6%
the atmospheric pressure at Earth's surface.
Topographic map of Mars, courtesy NASA/JPL-Caltech. Notable features include the Tharsis volcanoes in the west (including Olympus
Mons), Valles Marineris to the east of Tharsis, and Hellas Basin in the southern hemisphere.
Zero meridian: Mars' equator is defined by its rotation, but the location of its Prime Meridian was specified, as was Earth's, by choice of an arbitrary point
which was accepted by later observers. The German astronomers Wilhelm Beer
and Johann
Heinrich Mädler selected a small circular feature as a reference point when they produced the first systematic chart of Mars
features in 1830-32. In 1877, their choice was adopted as the prime meridian by the Italian
astronomer Giovanni Schiaparelli when he began work on
his notable maps of Mars. After the spacecraft Mariner 9 provided extensive
imagery of Mars in 1972, a crater (later called Airy-0), located in the Sinus Meridiani ('Middle
Bay' or 'Meridian Bay') along the line of Beer and Mädler, was chosen by Merton Davies of the RAND Corporation
to provide a more precise definition of 0.0° longitude when he established a geographic control point network.
Mars' 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.
Mars's natural satellites
| 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 |
As seen from Mars, Phobos has an angular diameter of about 12', while Deimos has an angular diameter of about 2'. The Sun's
angular diameter, by contrast, is about 21'.
The exploration of Mars
Main article: Exploration of Mars
Viking Lander 1 site (click for detailed description).
Dozens of spacecraft, including orbiters, landers, and rovers,
have been sent to Mars by the Soviet Union, the United States, Europe, and Japan to study the planet's surface, climate, and geography. Roughly two-thirds of all spacecraft
destined for Mars have failed in one manner or another before completing or even beginning their missions. Part of this high
failure rate can be ascribed to technical incompetence, but enough have either failed or lost communications for no apparent
reason that some researchers half-jokingly speak of an Earth-Mars "Bermuda Triangle" or of a Great Galactic Ghoul
which subsists on a diet of Mars probes.
Among the most successful missions are the Mariner and Viking programs, Mars Global Surveyor, Mars Pathfinder, and
Mars Odyssey. 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.
Mars Odyssey 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.
In 2003, the ESA
launched the Mars Express craft consisting of the Mars Express Orbiter and the lander Beagle 2. Mars Express Orbiter confirmed the presence of water ice and carbon dioxide ice at the planet's south
pole. NASA had previously confirmed their presence at the north pole of Mars. Attempts to contact the Beagle 2 failed and it was
declared lost in early February 2004.
Also in 2003, NASA launched the twin Mars Exploration Rovers named Spirit (MER-A) and Opportunity (MER-B). The spacecraft landed successfully
three weeks apart, activated their rover vehicles, sent back detailed panoramic photographs, and began geologic work. On March 2, 2004 NASA announced that the rovers had
uncovered convincing evidence that some parts of the surface of Mars were once covered in liquid water. This increases the
probability that some form of life once existed on Mars.
Miscellaneous
The "Ares Vallis" area as photographed by Mars Pathfinder (click for detailed description).
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 9:51:13 UT, Mars
made its closest approach to Earth in nearly 60,000 years: 55,758,006 km (approximately 35 million miles) without Light-time correction. This close approach came about because
Mars was one day from opposition and about three days
from its perihelion, making Mars particularly easy to see from Earth. The last
time it came so close is estimated to have been on September 12, 57,617 BC. Detailed analysis of the solar system's gravitational
landscape forecasts an even closer approach in 2287. However, to keep this in perspective,
this record approach was only an imperceptibly tiny fraction less than other recent close approaches that occur four times every
284 years. For instance, the minimum distance on August 22, 1924 was 0.37284 AU, compared to 0.37271 AU on
August 27, 2003, and the minimum distance
on August 24, 2208 will be 0.37278 AU.
A transit of the Earth as seen from Mars
will occur on November 10, 2084. At that time the Sun, the Earth and Mars will be exactly in a line. There are also transits of Mercury and transits of Venus, and the moon Deimos is of sufficiently small angular diameter that its partial "eclipses"
of the Sun are best considered transits (see Transit of Deimos from Mars).
Martian meteorites
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. 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.
In Solar
System Research (March 2004, vol 38, page 97) it was suggested that the unique Kaidun meteorite, recovered from
Yemen, may have originated on the Martian moon of Phobos.
On 14 April 2004, Nasa revealed that a rock known as "Bounce", studied by the Mars Exploration Rover Opportunity, was
similar in composition to the meteorite EETA79001-B, discovered in Antarctica
in 1979. The rock may have been ejected from the same crater as the meteorite, or from another crater in the same area of the
Martian surface.
Mars in various cultures
Ancient Egypt
In Ancient Egypt, this planet was known as "Horus the Red." Because of
Mars' retrograde motion, Egyptians said that it "traveled backwards." Also, Cairo's name
comes from "Al Qahira," which means the planet Mars in ancient Arabic.
Indian
In Jyotish, Mars is known in Sanskrit as Mangal (auspicious), Angaraka (burning coal), and Kuja (the fair one). It represents energetic action,
confidence and ego,
Related articles
Mars in religion
See also
External links
Water on Mars
Mars exploration
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