The fourth major planet from the Sun; the outermost of the terrestrial-type planets, with an eccentric orbit at a mean distance of 1·52 AU, and a diameter about half that of Earth. Its basic planetary characteristics are: mass 6·42 × 1023 kg; equatorial radius 3397 km/2111 mi; mean density 3·93 g/cm3; equatorial gravity 372 cm/s2; day (sidereal) 24 h 37 min 22 s; year 687 days; obliquity 25°11?; orbital eccentricity 0·093. A characteristically red planet, known to the ancients, it has been the subject of popular interest as a possible abode of life. There are two small natural satellites, Phobos and Deimos. Modern understanding dates back to the first spacecraft flyby of the planet in 1965 (NASA's Mariner 4) with later knowledge derived from Mariners 6 and 7, from the first planetary orbiter Mariner 9, from Viking landers and orbiters, and a series of orbiters and landers beginning with Mars Global Surveyor and the Pathfinder lander (with the Sojourner rover) which arrived in 1997, and continuing (after several failed missions) with the Mars Exploration Rovers (Spirit and Opportunity) in Jan 2004. It is a dry, cold planet with a thin, 95% carbon dioxide atmosphere. The atmospheric circulation has similarities to Earth's, but is marked by annual episodes of violent dust-storm activity that often escalate to planet-wide storms.
There is a complex surface of cratered uplands, lowland plains, and massive volcanic regions. The tilt of the rotational axis is similar to Earth's, and leads to marked seasonal variations. Seasonal polar caps of carbon dioxide grow to middle latitudes by the end of winter. There is an apparently permanent cap of water ice at the N pole. Polar regions show extensive sedimentary deposits with periodic layering - apparent evidence of periodic climate change. A variety of channel-like features (in popular tradition called canals) are observed - runoff channels a few tens of kilometres long and having tributaries; outflow channels of great size (tens of kilometres wide and hundreds long); and fretted channels that are wide and steep-walled. The runoff channels suggest that water once flowed on Mars early in the planet's history, when the climate might have been more clement. In 2004, the Mars Exploration Rover Opportunity revealed that rocks at its landing site were once in contact with substantial amounts of liquid water, suggesting that Mars had the right conditions to support life at some time in its history. The discovery of methane in the Martian atmosphere has also raised the possibility that a form of life may exist on Mars.
Volcanism is widespread, especially in the regions of Tharsis and Elysium. Tharsis volcanos are the largest and youngest, and lie on a pronounced crustal bulge - Olympus Mons reaches 27 km/16 mi in height, is c.700 km/435 mi across, and is capped by a caldera 80 km/50 mi across. The Valles Marineris is an equally spectacular canyon system, stretching a quarter of the way around the planet (over 4000 km/2500 mi), measuring 150700 km/100450 mi in width, and reaching depths of 27 km/14 mi. Soil coloration is due to the oxidation of iron minerals. Viking lander soil analysis revealed no organic material, even from meteorite falls, and indicates that the soil/atmospheric chemistry destroys organics. The possibility of biotic or prebiotic molecular evolution in earlier eras remains an intriguing question.
For other uses, including the Roman god, see Mars (disambiguation). Mars| Mars as seen by the Hubble Space Telescope | |
| Orbital characteristics (Epoch J2000) | |
|---|---|
| Semi-major axis |
227,936,637 km (141,632,976 mi) 1.523 662 31 AU |
| Orbital circumference |
1,429,000,000 km (887,900,000 mi) 9.553 AU |
| Eccentricity | 0.093 412 33 |
| Perihelion |
206,644,545 km (128,402,967 mi) 1.381 333 46 AU |
| Aphelion |
249,228,730 km (154.863,553 mi) 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 (53,859 mi/h) |
| Max. Orbital Speed | 26.499 km/s (59,277 mi/h) |
| Min. Orbital Speed | 21.972 km/s (49,150 mi/h) |
| 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 natural satellites | 2 |
| Physical characteristics | |
| Equatorial diameter |
6,804.9 km (4228.4 mi) (0.533 Earths) |
| Polar diameter |
6,754.8 km (4197.2 mi) (0.531 Earths) |
| Oblateness | 0.007 36 |
| Surface area |
1.448
×108 km² 55,907,000 square miles (144 798 465 square kilometers) |
| Volume |
1.6318
×1011 km³ |
| Mass |
6.4185
×1023 kg |
| Mean density | 3.934 g/cm³ |
| Equatorial gravity |
3.69 m/s2 (0.376g) |
| Escape velocity | 5.027 km/s (11,245 mi/h) |
| Rotation period |
1.025 957 d (24.622 962 h) |
| Rotation velocity |
868.22 km/h (539.49 mi/h) (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 |
−140 °C (133 K) −63 °C (210 K) 20 °C (293 K) |
| Adjective | Martian |
| Atmospheric characteristics | |
| Atmospheric pressure | 0.7–0.9 kPa |
| Carbon dioxide | 95.72% |
| 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 |
| edit | |
Mars (IPA: /ˈmɑɹz/ (GenAm); /ˈmɑːz/ (RP)) is the fourth planet from the Sun in our solar system and is named after Mars, the Roman god of war. Mars is also known as the "Red Planet" due to its reddish appearance when seen from Earth. The prefix areo-, from the Greek god of war, Ares, refers to Mars in the same way geo- refers to Earth.
Mars has two moons, Phobos and Deimos, which are small and oddly-shaped. Mars can be seen from Earth with the naked eye. For much of the year, Jupiter may appear brighter to the naked eye than Mars.
Until the first flyby of Mars by Mariner 4 in 1965, it was hoped, both within and especially perhaps outside scientific circles, especially in the popular media and literary circles, that Mars had ample liquid water. Still, of all the planets in our solar system other than Earth, Mars is the most likely to harbor liquid water, and perhaps life, so the myth has had enough influence that even now probes carry packages to attempt to find microscopic life.
Mars is currently host to four orbiting spacecraft: Mars Global Surveyor, Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter. Mars has half the radius of the Earth and only one-tenth the mass, being less dense, but its surface area is only slightly less than the total area of Earth's dry land. While Mars is larger and more massive than Mercury, Mercury has slightly stronger gravity at the surface, due to its much higher density.
Geology
The surface of Mars is thought to be primarily composed of basalt, based upon the Martian meteorite collection and orbital observations.
There is conclusive evidence that liquid water existed at one time on the surface of Mars.
Although Mars has no intrinsic magnetic field, observations have revealed that parts of the planet's crust have been magnetized. One theory, published in 1999 and reexamined in October 2005 with the help of the Mars Global Surveyor, is that these bands are evidence of the past operation of plate tectonics on Mars.
The geological history of Mars is split into three broad epochs:
Noachian epoch (named after Noachis Terra): Formation of Mars to between 3800 and 3500 million years ago.An alternative series of classifications, based on data from OMEGA Visible and Infrared Mineralogical Mapping Spectrometer on board the Mars Express orbiter has also been put forward.
Geography of Mars (Areography)
Although better remembered for mapping the Moon starting in 1830, Johann Heinrich Mädler and Wilhelm Beer were the first "areographers". In 1840, Mädler combined ten years of observations and drew the first ever map of Mars.
Today, features on Mars are named from a number of sources.
Since Mars has no oceans and hence no 'sea level', a zero-elevation surface or mean gravity surface must be selected. The surface of Mars as seen from Earth is thus divided into two kinds of areas, with differing albedo. The dark features were thought to be seas, hence their names Mare Erythraeum, Mare Sirenum and Aurorae Sinus.
Mars is also scarred by a number of impact craters. The largest of these is the Hellas impact basin, covered with light red sand.Despite being closer to the asteroid belt, there are far fewer craters on Mars compared with the Moon because Mars' atmosphere provides protection against small meteors.
Mars has two permanent polar ice caps, the northern one located at Planum Boreum and the southern one at Planum Australe.
The atmosphere of Mars is relatively thin; The atmosphere on Mars consists of 95% carbon dioxide, 3% nitrogen, 1.6% argon, and contains traces of oxygen and water. Methane is an unstable gas that is broken down by ultraviolet radiation, typically lasting in the atmosphere for about 340 years, and its possible presence on Mars could indicate that there is (or has been within the last few hundred years) a source of the gas on the planet. It was recently shown that methane could also be produced by a non-biological process involving water, carbon dioxide, and the mineral olivine, which is known to be common on Mars. Both Mars Global Surveyor and Mars Express have detected ionised atmospheric particles trailing off into space behind Mars.
If Mars had an Earthlike orbit, its seasons would be similar to Earth's because its axial tilt is similar to Earth's.
Mars also has the largest dust storms in the Solar System.
Mars possesses polar caps at both poles, which mainly consist of water ice. The northern polar cap has a diameter of approximately 1,000 kilometres during the northern Mars summer, and contains about 1.6 million cubic kilometres of ice, which if spread evenly on the cap would be 2 kilometres thick The southern polar cap has a diameter of 350 km, and a thickness of 3 km.
Orbit and rotation
Mars has a relatively pronounced orbital eccentricity of about 9%; The solar day (or sol) on Mars is only slightly longer than an Earth day: 24 hours, 39 minutes, and 35.244 seconds. As a result, Mars has seasons like the Earth, though Mars' are about twice as long given its longer year.
The image to the right shows a comparison between Mars and Ceres, a dwarf planet in the Asteroid Belt as seen from the ecliptic pole (top) and from the ascending node (below).
Moons
Mars has two tiny natural moons, Phobos and Deimos, which orbit very close to the planet and are thought to be captured asteroids.
From the surface of Mars, the motions of Phobos and Deimos appear very different from that of our own moon. Despite its 30 hour orbit, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars, and as long again to rise.
Because Phobos' orbit is below synchronous altitude, the tidal forces are lowering its orbit and in about 50 million years, it will either crash into Mars' surface or break up into a ring structure around Mars.
Famous literary author Jonathan Swift made reference to these moons of Mars, approximately 150 years before their actual discovery by Asaph Hall, detailing reasonably accurate descriptions of their orbits, in the 19th chapter of his novel Gulliver's Travels. They concluded that these were deposited by primitive life forms extant on Mars before the meteorite was blasted into space by a meteor strike and sent on a 15 million-year voyage to Earth.
In general, Mars shows some promise in terms of habitablity but also several handicaps.
Exploration
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 geology.
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 a Mars Curse, or even a reference made to a "Great Galactic Ghoul" that feeds on Martian spacecraft.
Past missions
The first successful fly-by mission to Mars was NASA's Mariner 4 launched in 1964. The first successful objects to land on the surface were two Soviet probes, Mars 2 and Mars 3 from the Mars probe program, launched in 1971, but both lost contact within seconds of landing. They also mapped the surface of Mars so well that the images are still sometimes used to this day. The Soviet probes Phobos 1 and 2 were also sent to Mars in 1988 to study Mars and its two moons, unfortunately Phobos 1 lost contact on the way to Mars, and Phobos 2, while successfully photographing Mars and Phobos, failed just before it was set to release two landers on Phobos' surface.
Current missions
Following the 1992 failure of Mars Observer orbiter, NASA launched the Mars Global Surveyor in 1996. Only a month after the launch of the Surveyor, NASA launched the Mars Pathfinder, carrying a robotic exploration vehicle, which landed in the Ares Vallis on Mars.
In 2001 NASA launched the successful Mars Odyssey orbiter, which is still in orbit as of August 2006.
In 2003, the ESA launched the Mars Express craft consisting of the Mars Express Orbiter and the lander Beagle 2.
Also in 2003, NASA launched the twin Mars Exploration Rovers named Spirit (MER-A) and Opportunity (MER-B).
On August 12, 2005 the NASA Mars Reconnaissance Orbiter probe was launched toward the planet, to conduct a two-year science survey. The next scheduled mission to Mars is the NASA Phoenix Mars lander, expected to launch in 2007.
Future plans
Future plans for unmanned Mars Exploration include the sending of the Phoenix Lander in 2007, followed by the Mars Science Laboratory in 2009, the Phobos-Grunt sample-return mission, to return samples of Phobos, a Martian moon.
Manned Mars exploration by the United States has been explicitly identified as a long-term goal in the Vision for Space Exploration announced in 2004 by US President George W.
The European Space Agency hopes to land the first humans on Mars between 2030 and 2035. This will be preceded by successively larger probes, starting with the launch of the ExoMars probe in 2013, followed by the 'Mars Sample Return Mission'.
Astronomical observations from Mars
See also: Timekeeping on MarsIt is now possible, with the existence of various orbiters, landers, and rovers to study astronomy from the Martian skies.
There are also various phenomena well-known on Earth that have now been observed on Mars, such as meteors and auroras. Auroras occur on Mars, but they do not occur at the poles as on Earth, because Mars has no planetwide magnetic field. Rather, they occur near magnetic anomalies in Mars's crust, which are remnants from earlier days when Mars did have a magnetic field.
A transit of the Earth as seen from Mars will occur on November 10, 2084. At that time, the Sun, Earth and Mars will be exactly collinear. 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 observed was that of October 3, 1590, seen by M.
Viewing Mars
See also: Aspects of MarsTo a naked-eye observer, Mars usually shows a distinct yellow, orange, or reddish color, and varies in brightness more than any other planet, as seen from Earth, over the course of its orbit. 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.
Approximately every 780 days opposition occurs, which is about when Mars is nearest to Earth.
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). This occurred when Mars was one day from opposition and about three days from its perihelion, making Mars particularly easy to see from Earth.
The orbital changes of Earth and Mars are making the approaches nearer: the 2003 record will be bettered 22 times by the year 4000.
Historical observations of Mars
The history of observations of Mars is marked by the oppositions of Mars, when the planet is closest to Earth and hence is most easily visible, which occur every couple of years. Even more notable are the perihelic oppositions of Mars which occur approximately every 16 years, and are distiguished because Mars is close to perihelion making it even closer to Earth. In that year, Italian astronomer Giovanni Schiaparelli, while in Milan, used a 22cm telescope to help produce the first detailed map of Mars. These canali were supposedly long straight lines on the surface of Mars to which he gave names of famous rivers on Earth. He published several books on Mars and life on Mars which had a great influence on the public.
The seasonal changes (consisting of the diminishing of the polar caps and the dark areas formed during Martian summer) in combination with the canals lead to speculation about life on Mars and it was a long held belief that Mars contained vast seas and vegetation.
Even in the 1960s articles were published on Martian biology, putting aside explanations other than life for the seasonal changes on Mars.
Some maps of Mars were made using the data from these missions, but it wasn't until the Mars Global Surveyor mission, launched in 1996 and still operational as of 2006, that complete, extremely detailed maps were obtained.
Mars in human culture
Historic connections
Mars is named after the Roman god of war. Then, following the identification of Ares and Mars, it was translated into Latin as stella Martis, or "star of Mars", or simply Mars. this is where one of the largest canyons on Mars, the Ma'adim Vallis, gets its name.
Its symbol, derived from the astrological symbol of Mars, a circle with a small arrow pointing out from behind it is a stylized representation of a shield and spear used by the Roman God Mars.
In fiction
The depiction of Mars in fiction has been stimulated by 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.
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. Mars (and its moons) were also the setting for the popular Doom video game franchise and the later Martian Gothic .
User Comments Add a comment…