Venus and Mars

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Venus

Click image for description
Orbital characteristics (Epoch J2000)
Semi-major axis	108,208,926 km 0.723 331 99 AU
Orbital circumference	0.680 Tm 4.545 AU
Eccentricity	0.006 773 23
Perihelion	107,476,002 km 0.718 432 70 AU
Aphelion	108,941,849 km 0.728 231 28 AU
Orbital period	224.700 69 d (0.615 197 0 a)
Synodic period	583.92 d
Avg. orbital speed	35.020 km/s
Max. orbital speed	35.259 km/s
Min. orbital speed	34.784 km/s
Inclination	3.394 71° (3.86° to Sun's equator)
Longitude of the ascending node	76.680 69°
Argument of the perihelion	54.852 29°
Number of satellites	0
Physical characteristics
Equatorial diameter	12,103.7 km (0.949 Earths)
Surface area	4.60×108 km2 (0.902 Earths)
Volume	9.28×1011 km³ (0.857 Earths)
Mass	4.8685×1024 kg (0.815 Earths)
Mean density	5.204 g/cm3
Equatorial gravity	8.87 m/s2 (0.904 gee)
Escape velocity	10.36 km/s
Rotation period	-243.0185 d
Rotation velocity	6.52 km/h (at the equator)
Axial tilt	2.64°
Right ascension of North pole	272.76° (18 h 11 min 2 s) 1
Declination	67.16°
Albedo	0.65
Surface* temp.	min* mean max 228 K 737 K 773 K
Adjective	Venusian or (rarely) Cytherean
(*min temperature refers to cloud tops only)
Atmospheric characteristics
Atmospheric pressure	9.3 MPa
Carbon dioxide	~96.5%
Nitrogen	~3.5%
Sulfur dioxide	.015%
Argon	.007%
Water vapor	.002%
Carbon monoxide	.0017%
Helium	.0012%
Neon	.0007%
Carbonyl sulfide Hydrogen chloride Hydrogen fluoride	trace

Venus, the second planet from the Sun, is named after the Roman goddess Venus. A terrestrial planet, it is sometimes called Earth's "sister planet", as the two are very similar in size and bulk composition. Although all planets' orbits are elliptical, Venus's orbit is the closest to circular, with an eccentricity of less than 1%. As Venus is closer to the Sun than the Earth, it always appears in roughly the same direction from Earth as the Sun (the greatest elongation is 47.8°), so on Earth it can usually only be seen a few hours before sunrise or a few hours after sunset. However, when at its brightest, Venus may be seen during the daytime, making it one of only two heavenly bodies that can be seen both day and night (the other being the Moon). It is sometimes referred to as the "Morning Star" or the "Evening Star", and when it is visible in dark skies it is by far the brightest star-like object in the sky.

The cycle between one maximum elongation and the next lasts 584 days. After these 584 days Venus is visible in a position 72 degrees away from the previous one. Since 5 * 584 = 2920, which is equivalent to 8 * 365 Venus returns to the same point in the sky every 8 years (minus two leap days). This was known as the Sothis cycle in ancient Egypt, and was familiar to the Maya as well. Another association is with the Moon, because 2920 days equal almost exactly 99 lunations (29.5 * 99 = 2920.5).

Venus has a very slow retrograde rotation, meaning that, unlike with most planets, the direction of rotation on its axis is the opposite of its orbital revolution around the Sun. The very slow rotation means that the distinction between its Sidereal day (rotation relative to the stars) and Solar day (relative to the Sun) is very significant.

The pentagram has long been associated with the planet Venus and the worship of the goddess Venus, or her equivalent. It is most likely to have originated from the observations of prehistoric astronomers. When viewed from Earth, the successive conjunctions of Venus plot the points of a pentagram around the Sun every eight years, returning to its starting point after a forty year cycle.

Venus was known to ancient Babylonians around 1600 BC, and to the Mayan civilization (the Mayans developed a religious calendar based on Venus's motion) and must have been known long before in prehistoric times, given that it is the third brightest object in the sky after the Sun and Moon. The Maasai people in Africa named the planet Kileken, and have a myth about it called "The Orphan Boy." The Morning Star was called the Bearer of Light ("phōsphoros" or "eōsphoros" in Greek and "Lucifer" in Latin, a term later used of the fallen angel cast out of heaven, see Isaiah 14:12). To the Jews it was known as Noga ("shining") and it was used in rabbinic literature as a symbol of beauty and purity

Its symbol is the sign also used in biology for the female sex, a stylized representation of the goddess Venus's hand mirror: a circle with a small cross underneath (Unicode: ♀). The Venus symbol also represents femininity, and in ancient alchemy stood for copper. Alchemists constructed the symbol from a circle (representing spirit) above a cross (representing matter).

The association with sex and femininity is supposed to relate to the period of 266 days between the conjunction and maximum elongation of Venus, which corresponds more or less to the length of human pregnancy.

The adjective Venusian is commonly used for Venus, but it is etymologically incorrect. The true adjective coming from Latin, Venereal, is avoided because of its modern association with sexually transmitted diseases. Some astronomers use Cytherean, which comes from Cythera. Other less common adjectives include Venerean, Venerian, and Veneran.

The Chinese, Korean, Japanese and Vietnamese cultures refer to the planet as the metal star, 金星, based on the Five Elements.

Contents 1 Physical characteristics 1.1 Atmosphere 1.2 Surface features 1.3 Venus' moon 2 Observations and explorations of Venus 3 Appearance 3.1 Lowest distances to earth 4 Cultural references 5 See also 6 References 6.1 Pentagram

Physical characteristics

Atmosphere

Venus has an atmosphere consisting mainly of carbon dioxide and a small amount of nitrogen, with a pressure at the surface about 90 times that of Earth (a pressure equivalent to a depth of 1 kilometer under Earth's oceans); its atmosphere is also roughly 90 times more massive than ours. This enormously CO₂-rich atmosphere results in a strong greenhouse effect that raises the surface temperature more than 400 °C (750 °F) above what it would be otherwise, causing temperatures at the surface to reach extremes as great as 500 °C (930 °F) in low elevation regions near the planet's equator. This makes Venus's surface hotter than Mercury's, even though Venus is nearly twice as distant from the Sun and only receives 25% of the solar irradiance (2613.9 W/m² in the upper atmosphere, and just 1071.1 W/m² at the surface). Owing to the thermal inertia and convection of its dense atmosphere, the temperature does not vary significantly between the night and day sides of Venus despite its extremely slow rotation of less than one rotation per Venusian year, meaning that, at the equator, Venus' surface rotates at a mere 6.5 km/h (4 mph). Upper atmosphere winds circling the planet approximately every 4 days help distribute the heat to other areas on the surface.

The solar irradiance is so much lower at the surface of Venus because the planet's thick cloud cover reflects the majority of the sunlight back into space. This prevents most of the sunlight from ever heating the surface. Venus's bolometric albedo is approximately 60%, and its visual light albedo is even greater. Thus, despite being closer to the Sun than Earth, the surface of Venus is not as well heated and even less well lit by the Sun. In the absence of any greenhouse effect, the temperature at the surface of Venus would be quite similar to Earth. A common conceptual misunderstanding regarding Venus is the mistaken belief that its thick cloud cover traps heat, as the opposite is actually true. The cloud cover keeps the planet much cooler than it would be otherwise. The immense quantity of CO₂ in the atmosphere is what traps the heat by the greenhouse mechanism.

There are strong 300 km/h (200 mph) winds at the cloud tops, but winds at the surface are very slow, no more than a few miles per hour. However, owing to the high density of the atmosphere at Venus's surface, even such slow winds exert a significant amount of force against obstructions. The clouds are mainly composed of sulfur dioxide and sulfuric acid droplets and cover the planet completely, obscuring any surface details from the human eye. The temperature at the tops of these clouds is approximately −45 °C (−50 °F). The mean surface temperature of Venus, as given by NASA, is 464 °C (864 °F). The minimal value of the temperature, listed in the table, refers to cloud tops —the surface temperature is never below 400 °C (750 °F). (This makes the surface temperature hot enough to melt lead.)

The atmosphere also contains hydrogen sulfide (H₂S) and carbonyl sulfide (SCO). Hydrogen sulfide reacts with sulfur dioxide, which implies that some process must be creating these components. It is unclear how the carbonyl sulfide could be formed--it is often a sign of biological activity. Some have suggested that microbes exist in the clouds (which also contain droplets of water), and produce these components from water, carbon monoxide and sulfur dioxide. New Scientist, Sept. 28, 2002, p. 16

Surface features

For more details on this topic, see Geology of Venus.

Venus has slow retrograde rotation, meaning it rotates from east to west, instead of west to east as most of the other major planets do. (Pluto and Uranus also have retrograde rotation, though Uranus's axis, tilted at 97.86 degrees, almost lies in its orbital plane.) It is not known why Venus is different in this manner, although it may be the result of a collision with a very large asteroid at some time in the distant past. If the Sun could be seen from Venus' surface, it would appear to rise and set in a 116.75 day cycle (Venus' synodic rotation period), and a Venusian year would thus last 1.92 Venusian "days".

In addition to this unusual retrograde rotation, the periods of Venus' rotation and of its orbit are synchronized in such a way that it always presents the same face toward Earth when the two planets are at their closest approach (5.001 Venusian days between each inferior conjunction). This may simply be a coincidence, but there is some speculation that this may be the result of tidal locking, with tidal forces affecting Venus' rotation whenever the planets get close enough together —although the tides raised by Earth on Venus are vanishingly small.

Venus has two major continent-like highlands on its surface, rising over vast plains. The northern highland is named Ishtar Terra and has Venus's highest mountains, named the Maxwell Montes (roughly 2 km taller than Mount Everest) after James Clerk Maxwell, which surround the plateau Lakshmi Planum. Ishtar Terra is about the size of Australia. In the southern hemisphere is the larger Aphrodite Terra, about the size of South America. Between these highlands are a number of broad depressions, including Atalanta Planitia, Guinevere Planitia, and Lavinia Planitia. With only the exception of Maxwell Montes, all surface features on Venus are named after real or mythological females. Venus' thick atmosphere causes meteors to decelerate as they fall toward the surface, and even large meteors will strike the surface at too low a speed to form an impact crater if they have less than a certain threshold kinetic energy. Because of this, no impact crater smaller than about 3 km (2 mi) in diameter can form.

Nearly 90% of Venus's surface appears to consist of recently (in the geological sense) solidified basaltic lava, with very few meteorite craters. The oldest features present on Venus seem to be only around 800 million years old, with most of the terrain being considerably younger (though still not less than several hundred million years for the most part). This suggests that Venus underwent a major resurfacing event in the not too distant geological past. The interior of Venus is probably similar to that of Earth: an iron core about 3000 km in radius, with a molten rocky mantle making up the majority of the planet. Recent results from the Magellan gravity data indicate that Venus's crust is stronger and thicker than had previously been assumed. It is theorized that Venus does not have mobile plate tectonics as Earth does, but instead undergoes massive volcanic upwellings at regular intervals that inundate its surface with fresh lava. Other recent findings suggest that Venus is still volcanically active in isolated geological hotspots.

Venus's intrinsic magnetic field has been found very weak compared to other planets in the solar system. This may be due to its slow rotation being insufficient to drive an internal dynamo of liquid iron. As a result, solar wind strikes Venus's upper atmosphere without mediation. It is thought that Venus originally had as much water as Earth, but that under the Sun's assault water vapor in the upper atmosphere was split into hydrogen and oxygen, with the hydrogen escaping into space owing to its low molecular mass; the ratio of hydrogen to deuterium (a heavier isotope of hydrogen which doesn't escape as quickly) in Venus's atmosphere seems to support this theory. Molecular oxygen is thought to have combined with atoms in the crust (large amounts of oxygen, however, remain in the atmosphere in the form of carbon dioxide). Because of their dryness, Venus's rocks are much harder than Earth's, which leads to steeper mountains, cliffs and other features.

Venus' moon

Venus was once thought to possess a moon, named Neith after the chief goddess of Sais, Egypt (whose veil no mortal raised), first observed by Giovanni Domenico Cassini in 1672. German astronomers called the moon Kleinchen (literally "tiny"), and sporadic sightings by astronomers continued until 1892. These sightings have since been discredited, and are thought to have been either spurious internal reflections, mostly faint stars that happened to be in the right place at the right time, or maybe even asteroids passing by the planet. Venus is now known to be moonless.

Observations and explorations of Venus

Main article: Observations and explorations of Venus

Venus has been observed several times within the past 4000 years by a number of people, including the Greeks.

Appearance

Greatest Eastern Elongation	Maximum brightness	Stationary, begin retrograde	Inferior Conjunction	Stationary, resume direct	Maximum brightness	Greatest Western Elongation	Superior Conjunction
March 29, 2004 46°	May 3, 2004	May 18, 2004	June 8, 2004	June 29, 2004	July 13, 2004	August 17, 2004 45.8°	March 31, 2005
November 3, 2005 47.1°	December 12, 2005	December 23, 2005	January 13, 2006	February 3, 2006	February 14, 2006	March 25, 2006 46.5°	October 27, 2006
June 9, 2007 45.4°	July 14, 2007	July 25, 2007	August 18, 2007	September 7, 2007	September 23, 2007	October 28, 2007 46.5°	June 9, 2008
January 14, 2009 47.1°	February 20, 2009	March 5, 2009	March 27, 2009	April 15, 2009	April 29, 2009	June 5, 2009 45.9°	January 11, 2010
August 20, 2010 46°	September 27, 2010	October 7, 2010	October 29, 2009	November 16, 2010	December 2, 2010	January 8, 2011 47°	August 16, 2011
March 27, 2012 46°	April 30, 2012	May 15, 2012	June 6, 2012	June 27, 2012	July 10, 2012	August 15, 2012 45.8°	March 28, 2013
November 1, 2013 47.1°	December 10, 2013	December 20, 2013	January 11, 2014	January 31, 2014	February 11, 2014	March 22, 2014 46.6°	October 25, 2014
June 6, 2015 45.4°	July 12, 2015	July 23, 2015	August 15, 2015	September 5, 2015	September 20, 2015	October 26, 2015 46.4°	June 6, 2016
January 12, 2017 47.1°	February 18, 2017	March 2, 2017	March 25, 2017	April 12, 2017	April 26, 2017	June 3, 2017 45.9°	January 9, 2018
August 17, 2018 45.9°	September 25, 2018	October 5, 2018	October 26, 2018	November 24, 2018	November 30, 2018	January 6, 2019 47°	August 14, 2019
March 24, 2020 46.1°	April 28, 2020	May 13, 2020	June 3, 2020	June 24, 2020	July 8, 2020	August 13, 2020 45.8°	March 26, 2021

Lowest distances to earth

At inferior conjunction, Venus can get closer to earth than any other planet--little more than 100 times the Moon's average distance. On December 16th, 1850, Venus reached since 1800 the lowest distance to earth with a value of 0,264138541298281 AU = 39514827 kilometres. This will be the closest approach of Venus to earth since December 16th, 2101 when Venus will reach a distance of 0,26431736 AU = 39541578 kilometres to earth.

Cultural references

See also Venus in fiction

Until it was penetrated by probes, Venus's opaque cloud layer gave science fiction writers free rein in imagining the planet's surface, and they frequently imagined it to be Earthlike. There are some religious sects who believe that Hell may be located on Venus. Its extremely high surface temperature and impenetrable cloud cover cause people to believe that the fires of Hell burn on the surface, obscured from our earthly view. Conversely, other sects consider Venus to be some form of paradise or an advanced secret base for angels/aliens to operate from.

• In Olaf Stapledon's epic Last and First Men (1930), Venus is an oceanic idyll where humans evolve the power of flight.
• In the mythology of Middle-earth (1937), by J. R. R. Tolkien, Venus is the Star of Eärendil. The star was created when Eärendil the Mariner was set in the sky on his ship, with a Silmaril bound to his brow. In fact, Tolkien chose the name directly from the ancient Old English word for the planet Venus.
• In H. P. Lovecraft's Cthulhu Mythos (1928–), there are mentions of the 'Lords of Venus', and conflicting indications that the Serpent People originated there.
• Edgar Rice Burroughs wrote a series of five books on Venus, featuring hero Carson Napier, who discovers that Venus (or Amtor, as it is known by the Venusians) is a world of sky-high trees, warring kingdoms and princesses in need of rescue. [1]
• The H. P. Lovecraft and Kenneth Sterling short story 'In the Walls of Eryx' (1939), takes place on Venus, but is not considered part of the Cthulhu Mythos.
• The second book of the Space Trilogy (1938–1945) by C.S. Lewis, Perelandra 1943) takes place on Venus (called by the natives Perelandra), the site of a second garden of Eden.
• In the military science fiction classic Clash by Night (1943) by Henry Kuttner (writing as Lawrence O'Donnell) and C. L. Moore, underwater city-states hire mercenary companies and their battleships to fight their wars on the surface.
• Venus was the home planet of the Mekon, arch-enemy of the 1950s comic book hero Dan Dare.
• Many science-fiction movies and serials of the '50s and '60s, such as Abbott and Costello Go to Mars and Space Patrol, have used Venus' namesake goddess and her domain to contrive planetary populations of nubile women welcoming (or attacking) all-male astronaut crews.
• In the Noon Universe created by the Soviet science fiction writers Boris and Arkady Strugatsky, Venus is depicted as a extremely harsh planet covered by strange flora and fauna but also very rich in minerals and heavy metals. The novel The Land of Crimson Clouds (Strana Bagrovykh Tuch in the original) describes the first successful manned mission to Venus, although a full-scaled colonization of the planet was not initiated until much later (in 2119; see Noon: 22nd Century).
• Venus is the location of several Starfleet Academy training facilities and terraforming stations in the fictional Star Trek universe (1966–).
• In Jacqueline Susann's Yargo (1979), Venus is inhabited by bees that are as big as horses.
• Venus is briefly mentioned in Arthur C. Clarke's 3001: The Final Odyssey (1997).
• A presumably terraformed Venus was the setting of one episode of the anime Cowboy Bebop (1998). In the show, Venus was revealed to be an arid but habitable world. Much of the population lived in floating cities in the sky. In the cartoon Exosquad, terraformed Venus was portrayed as one of the three habitable planets in the solar system (the others being Earth and Mars).
• In the Japanese anime series, Bishoujo Senshi Sailor Moon (1992), Sailor Venus is a soldier representing the planet of the same name. In mythology, Venus is the Roman goddess of love (Aphrodite in Greek), therefore, Sailor Venus's attacks and weapons (e.g. Venus Love Me Chain and Venus Love and Beauty Shock) represent the idea of love and femininity. Her image colours are gold and orange--similar to the colour of the planet. Also, on her forehead is the planet's symbol.
• A more scientifically accurate depiction of the planet is offered in Ben Bova's novel Venus (2000, ISBN 031287216X)-

See also

• Geology of Venus
• List of artificial objects on Venus
• List of mountains on Venus
• List of craters on Venus
• Planets in astrology
• Terraforming
• Transit of Venus
• Venus (mythology)

References

• Arnett, Bill (2005). Venus. Retrieved March 27, 2005.
• European Space Agency (2005). Venus Express overview. Retrieved March 27, 2005.
• Grayzeck, Ed (2004). Venus Fact Sheet. NASA. Retrieved March 27, 2005.
• Grieger, Bjoern (2004). Picture “Real Venus”. Retrieved March 27, 2005.
• The Maya Astronomy Page (2002). Venus. Retrieved March 27, 2005.
• Mitchell, Don P. (2004). The Soviet Exploration of Venus. Retrieved March 27, 2005.
• Rosenthal, David. (2003). THE SOUTHERNMOST RISE OF VENUS AT UXMAL, 1997. Retrieved March 27, 2005.
• Vienna University of Technology (2004). Venus Three-Dimensional Views. Retrieved March 27, 2005.
• Mallama, A. (1996). Schroeter's Effect and the twilight model for Venus. Journal of the British Astronomical Association 106 (1): 16–18. [2]
• 3D VRML Venus globe
• Venus Fact Sheet

Pentagram

• http://www.mikecrowson.co.uk/pentagram.html
• http://www.symbols.com/encyclopedia/29/2914.html
• http://www.hyperflight.com/venus-five-pointed-star.htm
• Venus Forum

The Solar System
Sun - Mercury - Venus - Earth (Moon) - Mars - Asteroid belt - Jupiter
Saturn - Uranus - Neptune - Pluto - Kuiper belt - Scattered disc - Oort cloud
See also astronomical objects and the solar system's list of objects, sorted by radius or mass.

This article is based on the article "Venus" from Wikipedia - the free encyclopedia created and edited by online user community. This article is distributed under the terms of GNU Free Documentation License. Here you find the list of authors of this article. The article can only edited within Wikipedia. Edit this article in Wikipedia.

For other uses, see Mars (disambiguation).

Mars

A composite image of Mars.
Orbital characteristics (Epoch J2000)
Semi-major axis	227,936,637 km (141,632,976 Miles) 1.523 662 31 AU
Orbital circumference	1.429 Tm (888,005,041 Miles) 9.553 AU
Eccentricity	0.093 412 33
Perihelion	206,644,545 km (128,402,710 Miles) 1.381 333 46 AU
Aphelion	249,228,730 km (154.863,243 Miles) 1.665 991 16 AU
Orbital period	686.9600 d (1.8808 a)
Synodic period	779.96 d (2.135 a)
Avg. Orbital Speed	24.077 km/s (53,820 Miles / Hour)
Max. Orbital Speed	26.499 km/s (59,220 Miles / Hour)
Min. Orbital Speed	21.972 km/s (49,140 Miles / Hour)
Inclination	1.850 61° (5.65° to Sun's equator)
Longitude of the ascending node	49.578 54°
Argument of the perihelion	286.462 30°
Number of satellites	2
Physical characteristics
Equatorial diameter	6,804.9 km (4228.4 Miles) (0.533 Earths)
Polar diameter	6,754.8 km (4197.2 Miles) (0.531 Earths)
Oblateness	0.007 36
Surface area	1.448×108 km2 (55.907 Million Square Miles) (0.284 Earths)
Volume	1.6318×1011 km3 (0.151 Earths)
Mass	6.4185×1023 kg (0.107 Earths)
Mean density	3.934 g/cm3
Equatorial gravity	3.69 m/s2 (0.376g)
Escape velocity	5.027 km/s (11,232 Miles / Hour)
Rotation period	1.025 957 d (24.622 962 h)
Rotation velocity	868.22 km/h (539.49 Miles / Hour) (at the equator)
Axial tilt	25.19°
Right ascension of North pole	317.681 43° (21 h 10 min 44 s)
Declination	52.886 50°
Albedo	0.15
Surface temp. - min - mean - max	133 K(-140 C) 210 K (-63 C) 293 K (20 C)
Adjective	Martian
Atmospheric characteristics
Atmospheric pressure	0.7-0.9 kPa
Carbon dioxide	95.32%
Nitrogen	2.7%
Argon	1.6%
Oxygen	0.13%
Carbon monoxide	0.07%
Water vapor	0.03%
Nitric oxide	0.01%
Neon	2.5 ppm
Krypton	300 ppb
Xenon	80 ppb
Ozone	30 ppb
Methane	10.5 ppb
edit

Mars is the fourth planet from the Sun in our solar system. It is named after the Roman god of war Mars (Ares in Greek mythology) because of its apparent red color. This feature also earned it the nickname "The Red Planet". Mars has two moons, Phobos and Deimos, which are small and oddly-shaped, possibly being captured asteroids. The prefix areo- refers to Mars in the same way geo- refers to Earth — for example, areology versus geology. (However, areology is also used to refer to the study of Mars as a whole rather than just the geological processes of the planet.)

The astronomical symbol for Mars is ♂, a circle with an arrow pointing northeast. This symbol is a stylized representation of the shield and spear of the god Mars, and in biology it is used as a sign for the male sex.

The Chinese, Japanese, Korean and Vietnamese cultures refer to the planet as 火星, or fire star, a naming based on the ancient Chinese mythological cycle of Five Elements.

Contents 1 Mythology 2 Physical characteristics 2.1 Atmosphere 2.2 Geology 2.3 Topography 2.4 Canals 2.5 Ice patches 3 The moons of Mars 4 The exploration of Mars 5 Nomenclature 5.1 Early nomenclature 5.2 Modern nomenclature 6 Observation of Mars 7 Appearance 8 Occultation of stars by Mars between 1800 and 2100 9 Martian meteorites 10 Life on Mars 11 The Mars flag 12 Mars in fiction 13 See also 14 References 15 External links 15.1 Water on Mars 15.2 Mars exploration

Mythology

Main article: Mars (god)

Mars has been obvious to skygazers since prehistoric times. It was known by the Egyptians as "Her Deschel" or "the Red One." Among the Babylonians Mars was known as "Nergal" or "the Star of Death." The Romans were the ones to give Mars its modern name, after their god of war.

Physical characteristics

The red, fiery appearance of Mars is caused by iron oxide (rust) on its surface. Mars has only a quarter the surface area of the Earth and only one-tenth the mass, though its surface area is approximately equal to that of the Earth's dry land because Mars lacks oceans. The solar day (or sol) on Mars is very close to Earth's day: 24 hours, 39 minutes, and 35.244 seconds.

Atmosphere

Mars' atmosphere is thin: the air pressure on the surface is only 750 pascals, about 0.75% of the average on Earth. However, the scale height of the atmosphere is about 11 km, somewhat higher than Earth's 6 km. The atmosphere on Mars is 95% carbon dioxide, 3% nitrogen, 1.6% argon, and contains traces of oxygen and water. The atmosphere is quite dusty, giving the Martian sky a tawny color when seen from the surface; data from the Mars Exploration Rovers indicates the suspended dust particles are roughly 1.5 microns across.^[1] In 2003, methane was apparently discovered in the atmosphere by Earth-based telescopes and possibly confirmed in March 2004 by the Mars Express Orbiter; present measurements state an average methane concentration of about 11±4 ppb by volume (see reference). The thin atmosphere cannot hold heat and is the cause of the lower temperatures on Mars. The maximum temperature is roughly 20℃ (68℉).

The presence of methane on Mars would be very 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 impacts, and the existence of life in the form of microorganisms such as methanogens are among possible but as yet unproven sources. The methane appears to occur in patches, which suggests that it is being rapidly broken down before it has time to become uniformly distributed in the atmosphere, and so it is presumably also continually being released to the atmosphere. Plans are now being made to look for other companion gases that may suggest which sources are most likely; in the Earth's oceans biological methane production tends to be accompanied by ethane, while volcanic methane is accompanied by sulfur dioxide.

Other aspects of the Martian atmosphere vary significantly. In the winter months when the poles are in continual darkness, the surface gets so cold that as much as 25% of the entire atmosphere condenses out into meters thick slabs of CO₂ ice (dry ice). When the poles are again exposed to sunlight the CO₂ ice sublimates, creating enormous winds that sweep off the poles as fast as 250 mph (402,33 km/h). These seasonal actions transport large amounts of dust and water vapor giving rise to Earth-like frost and large cirrus clouds. These clouds of water-ice were photographed by the Opportunity rover in 2004.[2]

Recently, evidence has been discovered suggesting that Mars may be warming in the short term[3]. However, it is now cooler than it was in the 1970s.[4]

Geology

The surface of Mars is thought to be primarily composed of basalt, based upon the Martian meteorite collection and orbital observations. There is some evidence that some portion of the Martian surface might be more silica-rich than typical basalt, perhaps similar to andesitic rocks on Earth, though these observations may also be explained by silica glass. Much of the surface is deeply covered by dust as fine as talcum powder.

Observations of the magnetic fields on Mars by the Mars Global Surveyor spacecraft have revealed that parts of the planet's crust has been magnetized. This magnetization has been compared to alternating bands found on the ocean floors of Earth. One interesting theory, published in 1999 and reexamined in October 2005 in a publication by the same group, is that these bands could be evidence of the past operation of plate tectonics on Mars. However, this has yet to be proven [5] or widely accepted and remains an area of active research.

Amongst the findings from the Opportunity rover is the presence of hematite on Mars in the form of small spheres on the Meridiani Planum. The spheres are only a few millimeters in diameter and are believed to have formed as rock deposits under watery conditions billions of years ago. Other minerals have also been found containing forms of sulfur, iron or bromine such as jarosite. This and other evidence led a group of 50 scientists to conclude in the December 9, 2004 edition of the journal Science that "Liquid water was once intermittently present at the Martian surface at Meridiani, and at times it saturated the subsurface. Because liquid water is a key prerequisite for life, we infer conditions at Meridiani may have been habitable for some period of time in Martian history". Later studies suggested that this liquid water was actually acid because of the types of minerals found at the location. On the opposite side of the planet the mineral goethite, which (unlike hematite) forms only in the presence of water, along with other evidence of water, has also been found by the Spirit rover in the "Columbia Hills".

In 1996, researchers studying a meteorite (ALH84001) believed to have originated from Mars reported features which they attributed to microfossils left by life on Mars. As of 2005, this interpretation remains controversial with no consensus having emerged.

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 plain). The dark features were thought to be seas, hence their names Mare Erythraeum, Mare Sirenum and Aurorae Sinus. The largest dark feature seen from Earth is Syrtis Major.

Mars has polar ice caps that contain frozen water and carbon dioxide that change with the Martian seasons &mdash. Each cap has surface deposits of carbon dioxide ice that form a polar "hood" during Martian winter, and then sublimate during the summer uncovering the underlying cap surface of layered water ice and dust. The southern polar cap differs from the Northern polar cap in that it appears to contain at least some permanent deposits of CO2, which are changing on the time scale of years.

The shield volcano, Olympus Mons (Mount Olympus), is at 26 km the highest mountain in the solar system. It is in a vast upland region called Tharsis, which contains several large volcanos. See list of mountains on Mars. The Tharsis region of Mars also has the solar system's largest canyon system, Valles Marineris or the Mariner Valley, 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 difference between Mars' highest and lowest points is nearly 31 km (from the top of Olympus Mons at an altitude of 26 km to the bottom of the Hellas impact basin at an altitude of 4 km below the datum). In comparison, the difference between Earth's highest and lowest points (Mount Everest and the Mariana Trench) is only 19.7 km. Combined with the planets' different radii, this means Mars is nearly three times "rougher" than Earth.

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 for Mars is defined by the fourth-degree and fourth-order spherical harmonic gravity field, with the zero altitude defined by the 610.5 Pa (6.105 mbar) atmospheric pressure surface (approximately 0.6% of Earth's) at a temperature of 273.16 K. This pressure and temperature correspond to the triple point of water.

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 small 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 planetographic control point network.

Canals

Mars has an important place in human imagination due to the belief by some that life existed on Mars. These beliefs are due mainly to observations by many in the 19th century popularized by Percival Lowell and Giovanni Schiaparelli. Schiaparelli called these observed features canali, meaning channels in Italian. This was popularly mistranslated as 'canals', and the myth of the Martian canals began. They were apparently artificial linear features on the surface that were asserted to be 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.

Ice patches

On 29 July 2005, the BBC reported that a visible "ice lake" had been discovered in a crater in the north polar region of Mars. [6] Images of the crater, taken by the High Resolution Stereo Camera on board the European Space Agency's Mars Express spacecraft, clearly show a broad sheet of ice in the bottom of an unnamed crater located on Vastitas Borealis, a broad plain that covers much of Mars' far northern latitudes, at approximately 70.5° North and 103° East. The crater is 35 km (23 mi) wide and about 2 km (1.2 mi) deep.

According to the original HRSC/Mars Express feature [7], the height difference between the crater floor and the surface of the water ice is about 200 metres. ESA scientists have attributed most of this height difference to sand dunes beneath the water ice, which are partially visible. While scientists do not refer to the patch as a "lake", the water ice patch is remarkable for its size and for being present throughout the year. Deposits of water ice and layers of frost have been found in many different locations on the planet.

The moons of Mars

Main article: Mars' natural satellites

Mars has two tiny natural moons, Phobos and Deimos, which orbit very close to the planet and are thought to be captured asteroids.

The exploration of Mars

Main article: Exploration of Mars

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 problems, 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, or of a Mars Curse.

Among the most successful missions are the Mars probe program, 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. Another possible origin proposed for these gully features is transient melting of surface water snow, frost, or ice. Mars Odyssey determined that there are significant deposits of water ice in the upper meter or so of Mars' regolith within 30° of the north and south pole.

In 2003, the ESA launched the Mars Express craft consisting of the Mars Express Orbiter and the lander Beagle 2. 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). Both missions landed successfully in January 2004 and have met or exceeded all their targets; while a 90-day nominal mission was planned, as of February 2005, their missions have been extended twice and they continue to return science, although some mechanical faults have occurred. Among the most significant science return has been evidence of liquid water some time in the past at both landing sites. In addition, dust devils imaged from ground-level have been detected moving across the surface of Mars by Spirit (MER-A). Dust devils have even passed over the Rovers, cleaning the solar panels in the process. (See picture below). Dust devils were first imaged on Mars from the surface by Mars Pathfinder.

Nomenclature

Early nomenclature

Although better remembered for mapping the Moon starting in 1830, Johann Heinrich Mädler and Wilhelm Beer were the first "areographers". They started off by establishing once and for all that most of the surface features were permanent, and pinned down Mars' rotation period. In 1840, Mädler combined ten years of observations and drew the first map of Mars ever made. Rather than giving names to the various markings they mapped, Beer and Mädler simply designated them with letters; Meridian Bay (Sinus Meridiani) was thus feature "a".

Over the next twenty years or so, as instruments improved and the number of observers also increased, various Martian features acquired a hodge-podge of names. To give a couple of examples, Solis Lacus was known as the "Oculus" (the Eye), and Syrtis Major was usually known as the "Hourglass Sea" or the "Scorpion". In 1858, it was also dubbed the "Atlantic Canale" by the Jesuit astronomer Angelo Secchi. Secchi commented that it "seems to play the role of the Atlantic which, on Earth, separates the Old Continent from the New" —this was the first time the fateful canale, which in Italian can mean either "channel" or "canal", had been applied to Mars.

In 1867, Richard Anthony Proctor drew up a map of Mars based, somewhat crudely, on the Rev. William Rutter Dawes' earlier drawings of 1865, then the best ones available. Proctor explained his system of nomenclature by saying, "I have applied to the different features the names of those observers who have studied the physical peculiarities presented by Mars." Here are some of his names, paired with those later proposed by Schiaparelli:

• Kaiser Sea = Syrtis Major
  

  

  Artistic map of Mars with feature names by Schiaparelli
• Lockyer Land = Hellas
• Main Sea = Lacus Moeris
• Herschel II Strait = Sinus Sabaeus
• Dawes Continent = Aeria and Arabia
• De La Rue Ocean = Mare Erythraeum
• Lockyer Sea = Solis Lacus
• Dawes Sea = Tithonius Lacus
• Madler Continent = Chryse, Ophir, Tharsis
• Maraldi Sea = Mares Sirenum and Cimmerium
• Secchi Continent = Memnonia
• Hooke Sea = Mare Tyrrhenum
• Cassini Land = Ausonia
• Herschel I Continent = Zephyria, Aeolis, Aethiopis
• Hind Land = Libya

Proctor's nomenclature has often been criticized, mainly because so many of his names honored English astronomers, but also because he used many names more than once. In particular, Dawes appeared no fewer than six times (Dawes Ocean, Dawes Continent, Dawes Sea, Dawes Strait, Dawes Isle, and Dawes Forked Bay). Even so, Proctor's names are not without charm, and for all their shortcomings they were a foundation on which later astronomers would improve.

Modern nomenclature

Today, features on Mars derive from a number of sources. Large albedo features retain many of the older names, but are often updated to reflect new knowledge of the nature of the features. For example 'Nix Olympica' (the snows of Olympus) has become 'Olympus Mons' (Mount Olympus).

Large Martian craters are named after important scientists and science fiction writers; smaller ones are named after towns and villages on Earth.

Observation of Mars

Earth passes Mars every 780 days (or two years plus seven weeks and one day) at a distance of about 80,000,000 km. However, this varies because the orbits are elliptical. To a naked-eye observer, Mars usually shows a distinct yellow, orange or reddish colour, and varies in brightness more than any other planet as seen from Earth over the course of its orbit, due to the fact that when furthest away from the Earth it is more than seven times as far from the latter as when it is closest (and can be lost in the Sun's glare for months at a time when least favourably positioned). At its most favourable times — which occur twice every 32 years, alternately at 15 and 17-year intervals, and always between late July and late September — Mars shows a wealth of surface detail to a telescope. Especially noticeable, even at low magnification, are the polar ice caps.

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).

The only occultation of Mars by Venus to be observed was that of October 3, 1590, seen by M. Möstlin at Heidelberg.

Appearance

Stationary, retrograde	Opposition	Minimum distance to Earth (AU)	Maximum brightness (mag)	Diameter (Arcseconds)	Stationary, prograde	Conjunction to Sun
July 30, 2003	August 28, 2003	0.37271	-2.9	25.11"	September 29, 2003	September 15, 2004
October 1, 2005	November 7, 2005	0.46407	-2.3	20.17"	December 10, 2005	October 23, 2006
November 15, 2007	December 24, 2007	0.58936	-1.6	15.88"	January 30, 2008	December 5, 2008
December 21, 2009	January 29, 2010	0.66399	-1.3	14.10"	March 11, 2010	February 4, 2011
January 25, 2012	March 3, 2012	0.67368	-1.2	13.89"	April 15, 2012	April 18, 2013
March 1, 2014	April 8, 2014	0.61756	-1.5	15.16"	May 21, 2014,	June 14, 2015
April 17, 2016,	May 22, 2016	0.50321	-2.1	18.60"	June 30, 2016	July 27, 2017
June 28, 2018	July 27, 2018	0.38495	-2.8	24.31"	August 28, 2018	September 2, 2019
September 9, 2020	October 13, 2020	0.41491	-2.6	22.56"	November 15, 2020	October 8, 2021

Occultation of stars by Mars between 1800 and 2100

Date	Time	Star	Brightness of Star	Right ascension of star (Actual Equinox)	Declination of star (Actual Equinox)
1801 January 21	15h 26,6m UTC	DELTA ARIETIS	4,5	3 11 35,587	19 43 37,71
1802 July 11	8h 44,8m UTC	SIGMA ARIETIS	5,5	2 51 29,161	15 5 0,05
1803 December 04	20h 36,4m UTC	24 OPHIUCHI	5,6	16 56 48,069	-23 8 59,31
1812 October 26	13h 35,2m UTC	13 VIRGINIS	6,0	12 18 39,899	- 0 47 10,84
1825 May 25	14h 30,1m UTC	56 TAURI	5,3	4 19 36,333	21 46 31,79
1831 March 17	23h 18,6m UTC	37 TAURI	4,5	4 4 40,602	22 5 4,81
1839 August 07	15h 11,0m UTC	76 VIRGINIS	5,4	13 32 58,407	-10 9 47,91
1843 August 24	11h 36,6m UTC	36 OPHIUCHI	4,5	17 15 26,500	-26 33 11,33
1846 April 04	12h 44,3m UTC	YPSILON TAURI	4,4	4 26 17,255	22 48 55,94
1873 February 26	22h 11,0m UTC	MY LIBRAE	5,3	14 49 19,626	-14 8 54,60
1875 June 30	5h 53,0m UTC	3 SAGITTARII	4,7	17 47 33,659	-27 49 49,51
1893 May 07	20h 45,2m UTC	132 TAURI	5,0	5 49 0,873	24 34 4,00
1905 October 20	11h 12,8m UTC	SAO 187216	5,8	18 44 49,611	-25 0 37,33
1909 March 07	8h 13,2m UTC	SAO 187080	5,8	18 38 30,719	-23 30 15,84
1914 March 30	12h 38,3m UTC	52 GEMINORUM	6,0	7 14 41,634	24 53 13,62
1918 April 11	11h 57,0m UTC	SAO 118735	6,0	11 14 1,580	8 3 47,23
1918 October 28	2h 23,8m UTC	OMICRON OPHIUCHI	5,3	17 18 1,032	-24 17 12,22
1921 March 10	2h 24,2m UTC	ZETA PISCIUM	5,3	1 13 43,135	7 34 35,66
1922 January 26	11h 34,9m UTC	NY LIBRAE	5,3	15 6 37,793	-16 15 22,73
1934 May 29	9h 13,6m UTC	13 TAURI	5,7	3 42 18,921	19 42 1,78
1941 June 27	21h 42,7m UTC	27 PISCIUM	5,0	23 58 40,598	- 3 33 17,31
1957 November 18	8h 59,4m UTC	LAMBDA VIRGINIS	4,6	14 19 6,641	-13 22 17,18
1965 May 21	12h 0,5m UTC	CHI LEONIS	4,7	11 5 1,829	7 20 11,27
1966 April 16	18h 38,8m UTC	SAO 92659	6,0	1 50 52,132	11 2 37,10
1976 April 08	0h 57,6m UTC	EPSILON GEMINORUM	3,2	6 43 55,936 25	7 52,35
1989 February 17	9h 28,0m UTC	RHO ARIETIS	5,7	2 56 25,941	18 1 25,61
1992 April 30	17h 37,4m UTC	20 PISCIUM	5,7	23 47 56,494	- 2 45 41,79
1994 July 13	6h 21,6m UTC	53 TAURI	5,5	4 19 26,086	21 8 32,54
2013 July 31	14h 18,2m UTC	SAO 78816	5,8	6 51 59,948	23 36 6,05
2015 October 18	19h 26,7m UTC	CHI LEONIS	4,7	11 5 0,662	7 20 8,88
2032 January 23	12h 18,1m UTC	96 AQUARII	5,7	23 19 24,409	- 5 7 28,32
2035 March 12	4h 54,1m UTC	SAO 187080	5,8	18 38 30,714	-23 30 18,31
2036 March 29	21h 50,3m UTC	72 TAURI	5,5	4 27 17,447	22 59 46,33
2054 June 26	12h 48,2m UTC	OMICRON PISCIUM	4,4	1 45 23,891	9 9 29,97
2063 April 11	10h 1,3m UTC	47 LIBRAE	6,0	15 55 0,316	-19 22 59,70
2063 September 14	0h 46,7m UTC	SAO 184892	6,0	16 59 57,718	-25 5 32,87
2067 May 19	9h 34,4m UTC	IOTA AQUARII	4,3	22 6 26,417	-13 52 14,70
2068 December 22	19h 12,2m UTC	OMEGA SCORPII	4,5	16 7 24,542	-20 52 10,68
2078 March 19	12h 48,4m UTC	MY LIBRAE	5,3	14 49 18,697	-14 8 57,64
2078 October 03	22h 0,3m UTC	THETA OPHIUCHI	3,2	17 22 0,527	-25 0 0,23
2079 May 15	20h 12,8m UTC	KAPPA TAURI	5,3	4 25 25,658	22 11 56,26
2079 June 08	11h 51,1m UTC	121 TAURI	5,4	5 35 27,217	24 2 20,91
2086 June 07	15h 41,6m UTC	80 PISCIUM	5,6	1 8 20,760	5 38 45,05

Martian meteorites

Main article: 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 April 14, 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.

Life on Mars

Main article: Life on Mars

Some evidence suggests that the planet once was significantly more habitable than today, but the question on whether living organisms ever actually existed there is an open one. Some researchers think that a certain rock which is believed to have originated on Mars - specifically, meteorite ALH84001 - does contain evidence of past biologic activity, but no consensus about these claims has been achieved so far and recent research indicates that the rock, since its creation several billion years ago, has never been exposed to temperatures for extended periods of time that would allow for liquid water.

The Viking probes carried experiments designed to detect microorganisms in Martian soil at their respective landing sites, and had some positive results, later denied by many scientists, resulting in ongoing controversy. Also, present biologic activity is one of the explanations that have been suggested for the presence of traces of methane within the Martian atmosphere, but other explanations not involving life are generally considered more likely.

If colonization is going to happen, Mars seems a likely choice due to its rather hospitable conditions (compared with other planets, it is most like Earth).

The Mars flag

In early 2000, a proposed Mars flag flew aboard the space shuttle Discovery. Designed by NASA engineer and Flashline Mars Arctic Research Station task force leader Pascal Lee and carried aboard by astronaut John Mace Grunsfeld, the flag consists of three vertical bars (red, green, and blue), symbolizing the transformation of Mars from a barren planet (red) to one bearing sustainable life (green), and finally to a fully terraformed planet with open bodies of water. This design was suggested by the Kim Stanley Robinson sci-fi trilogy Red Mars, Green Mars, and Blue Mars. While other designs have been proposed, the republican tricolor has been adopted by the Mars Society as its own official banner. In a statement released after the launch of the mission, the Society said that the flag "has now been honored by a vessel of the leading spacefaring nation on Earth," and added that "(i)t is fitting that this action occurred when it did: at the dawning of a new millenium."

Mars in fiction

Main article: Mars in fiction

The depiction of Mars in fiction has been stimulated its dramatic red color and by early scientific speculations that its surface conditions might be capable of supporting life.

Until the arrival of planetary probes, the traditional view of Mars derived from the astronomers Percival Lowell and Giovanni Schiaparelli, whose observation of supposedly linear features on the planet created the myth of canals on Mars. For many years, a standard notion of the planet as a drying, cooling, dying world with ancient civilizations constructing irrigation works. Thus originated a large number of science fiction scenarios, the best known of which is H. G. Wells' The War of the Worlds, in which Martians seek to escape their dying planet by invading Earth.

After the Mariner and Viking spacecraft had returned pictures of Mars as it really is, an apparently lifeless and canal-less world, these ideas about Mars had to be abandoned and a vogue for accurate, realist depictions of human colonies on Mars developed, the best known of which may be Kim Stanley Robinson's Mars trilogy. However, pseudo-scientific speculations about the Face on Mars and other enigmatic landmarks spotted by space probes have meant that ancient civilizations continue to be a popular theme in science fiction, especially in film.

Another popular theme, particularly among American writers, is the Martian colony that fights for independence from Earth. This is a major plot element in the novels of Greg Bear and Kim Stanley Robinson, as well as the movie Total Recall (based on a novel by Philip K. Dick) and the television series Babylon 5. Many video games also use this element, such as Red Faction.

See also

• Areography
• Astrobiology
• Astronomy on Mars
• Colonization of Mars
• Darian calendar
• Face on Mars photo article
• Timekeeping on Mars
• Exploration of Mars
• List of artificial objects on Mars
• List of craters on Mars
• List of mountains on Mars
• Martian meteorite
• Mars photos
• Mars in fiction
• Extraterrestrial life
• Terraforming
• Mars Direct
• Mars in astrology
• Ares
• Tyr
• Richard C. Hoagland

References

• William Sheehan, The Planet Mars: A History of Observation and Discovery, The University of Arizona Press, Tucson, 1996
• Vladimir A. Krasnopolsky, Jean-Pierre Maillard, Tobias C. Owen, Detection of methane in the Martian atmosphere: evidence for life?, Icarus, 172 (2), 537-547.

^  Lemmon et al., "Atmospheric Imaging Results from the Mars Exploration Rovers: Spirit and Opportunity"

External links

• NASA's Mars fact sheet
• Nine Planets Mars page
• MarsNews.com - News and info site
• Introduction to Martian topography, with Hubble Space Telescope photos
• FU Berlin: HRSC (camera) experiment at Mars Express (eng. & ger.; press releases and high resolution images)
• Technical Notes about Time on Mars
• On Mars: Exploration of the Red Planet 1958-1978 from the NASA History Office.
• The Mars Society flag
• A Trip Into Space Photos and descriptions of Mars
• Martian Law - a CATO white paper
• Mars Unearthed - Comparisons of terrains between Earth and Mars
• 3D VRML Mars globe
• Enterprise Mission: Richard C. Hoagland's Homepage

Water on Mars

• Highly visible ice lake found on Mars - BBC
• Dr. Tony Phillips: "Making a Splash on Mars", Science@NASA article, June 29, 2000. Phillips describes the Martian "gullies" and explains the conditions under which liquid water can exist on the surface of Mars.
• BBC News story on subsurface ice deposits on Mars
• BBC News update on Mars Express' findings of polar water ice and water-eroded features on the surface
• Mars Rover Scientists Wring Water Story from Rocks This image taken by Mars Rover Opportunity shows microscopic rock forms indicating past signs of water. Courtesy: NASA
• BBC News Mars pictures reveal frozen sea

Mars exploration

• The Political Economy of Very Large Space Projects (Journal Of Evolution and Technology)
• exploreMarsnow Interactive Mars base simulation. Winner of 2003 Webby Award for Science.
• NASA Mars Exploration Rover Home Page
• Be on Mars Anaglyphs from the Mars Rovers (3D)

Mars' natural satellites edit
Phobos | Deimos

The Solar System
Sun - Mercury - Venus - Earth (Moon) - Mars - Asteroid belt - Jupiter
Saturn - Uranus - Neptune - Pluto - Kuiper belt - Scattered disc - Oort cloud
See also astronomical objects and the solar system's list of objects, sorted by radius or mass.

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