Portal:Mars
Portal maintenance status: (August 2018)
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Introduction
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English, Mars carries a name of the Roman god of war, and is often referred to as the "Red Planet" because the reddish iron oxide prevalent on its surface gives it a reddish appearance that is distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth.
The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan.
Selected general articles
The Tharsis region (shown in shades of red and brown) dominates the western hemisphere of Mars as seen in this Mars Orbiter Laser Altimeter (MOLA) colorized relief map. Tall volcanoes appear white. The Tharsis Montes are the three aligned volcanoes left of center. Olympus Mons sits off to the northwest. The oval feature in the north is Alba Mons. The canyon system Valles Marineris stretches eastward from Tharsis; from its vicinity, outflow channels that once carried floodwaters extend north.
Tharsis is a vast volcanic plateau centered near the equator in the western hemisphere of Mars. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons, which are collectively known as the Tharsis Montes. The tallest volcano on the planet, Olympus Mons, is often associated with the Tharsis region but is actually located off the western edge of the plateau. The name Tharsis is the Greco-Latin transliteration of the biblical Tarshish, the land at the western extremity of the known world. Read more...- Softened terrain in Argyre Planitia, 39 °S. Image is around 25 km across. Note the lack of any sharp ridges anywhere in the image.
The landscape polewards of around 30 degrees latitude on Mars has a distinctively different appearance to that nearer the equator, and is said to have undergone terrain softening. Softened terrain lacks the sharp ridge crests seen near the equator, and is instead smoothly rounded. This rounding is thought to be caused by high concentrations of water ice in soils. The term was coined in 1986 by Steve Squyres and Michael Carr from examining imagery from the Viking missions to Mars.
Below 30 degrees of latitude, impact craters have steep walls; well-defined, sharp rims; and flat or smoothly bowl-shaped floors. Ridges on intercrater plains come to similarly well-defined, pointed crests. However, above this latitude, these same features appear very different. The crests seen on ridges and crater rims appear strongly rounded and much more poorly defined. The relief (height) of features is somewhat reduced. Small craters are noticeably less common. In other words, terrain which elsewhere looked sharp here looks "soft". This texture has also been described as "smooth", or "rolling". Softened craters are also commonly infilled with concentric patterns on their floors.
On Earth, diffusive creep of soils is associated with rounded hillslopes. Squyres and Carr thus attributed the softened texture to accelerated viscous creep in shallow soils near the surface, and went on to associate this accelerated creep with the presence of ground ice at these latitudes. This conclusion has been largely borne out by subsequent research. In the late 1980s some attempts were made to link terrain softening with dust and aeolian processes, though this hypothesis has largely been superseded by more recent observations. Read more... - The composition of Mars covers the branch of the geology of Mars that describes the make-up of the planet Mars. Read more...
"Hottah" rock outcrop on Mars – ancient streambed viewed by the Curiosity Rover (September 12, 2012, white balanced) (raw) (close-up) (3-D version).
Stickney is the largest crater on Phobos, which is a satellite of Mars. It is 9 km (5.6 mi) in diameter, taking up a substantial proportion of the moon's surface.
The crater is named after Chloe Angeline Stickney Hall, wife of Phobos's discoverer, Asaph Hall. In 1878 Hall wrote that he "might have abandoned the search [for Martian satellites] had it not been for the encouragement of [his] wife." The crater was named in 1973, based on Mariner 9 images, by an IAU nomenclature committee chaired by Carl Sagan.
Stickney has a smaller crater within it, about 2 km (1.2 mi) in diameter, resulting from a later impact. In 2006 it was given the name Limtoc, after a character in Gulliver's Travels. Read more...- The target landing zone was a region near the south pole of Mars, called Ultimi Scopuli, because it featured a large number of scopuli (lobate or irregular scarps). Read more...
- Mars has two moons, Phobos and Deimos. Due to their small size, both moons were discovered only in 1877, by astronomer Asaph Hall. Nevertheless, they frequently feature in works of science fiction.
Some of the earliest mentions of Mars's moons in fiction predate their discovery. In Jonathan Swift's famous satire Gulliver's Travels (1726), the astronomers of flying island Laputa are described as having discovered two satellites of Mars. Voltaire's short story "Micromégas" (1752), about alien visitors from Sirius and Saturn, also describes Mars as having two moons. Voltaire is thought to have been influenced by Swift. In recognition of these mentions, many geological features of Phobos and Deimos are named after characters and places from Gulliver's Travels, including among others Laputa Regio and Lagado Planitia on Phobos, and craters Swift and Voltaire on Deimos. Read more...
The orbit of Mars (yellow band; varies between 1.381 and 1.666 AU) displayed with 6 theoretically possible orbits for an asteroid (red line). The orbit of a Mars-crosser is displayed in the bottom row on the right. In generic terms, a Mars-crosser has a smaller perihelion and a larger aphelion compared to Mars.
Special cases include inner-grazers (top row, in the middle) and outer-grazers (bottom row, in the middle), which do not completely cross the orbital band described by Mars. The other three diagrams describe a co-orbital configuration (top row, on the right) where the asteroid's orbit is contained within the orbital band of Mars, as well as a near-Earth asteroid such as an Amor asteroid (top row, on the left) and a main-belt asteroid, for example of the Hungaria family, which orbits are contained completely either inside or outside the orbit of Mars, respectively.
A Mars-crossing asteroid (MCA, also Mars-crosser, MC) is an asteroid whose orbit crosses that of Mars. The known numbered Mars-crossers are listed here. They include the two numbered Mars trojans 5261 Eureka and (101429) 1998 VF31.
Many databases, for instance the JPL Small-Body Database (JPL SBDB), only list asteroids with a perihelion greater than 1.3 AU as Mars-crossers. An asteroid with a perihelion less than this is classed as a near-Earth object even though it is crossing the orbit of Mars as well as crossing (or coming near to) that of Earth. Nevertheless, these objects are listed on this page. A grazer is an object with a perihelion below the aphelion of Mars (1.67 AU) but above the Martian perihelion (1.38 AU). The JPL SBDB lists 13,500 Mars-crossing asteroids. Only 18 MCAs are brighter than absolute magnitude (H) 12.5, which typically makes these asteroids with H<12.5 more than 13 km in diameter depending on the albedo. The smallest known MCAs have an absolute magnitude (H) of around 24 and are typically less than 100 meters in diameter. Read more...
The preservation and cementation of aeolian dune stratigraphy in Burns Cliff in Endurance Crater are thought to have been controlled by flow of shallow groundwater.
During past ages, there was rain and/or snow on Mars; especially in the Noachian and early Hesperian epochs. Some moisture entered the ground and formed aquifers. That is, the water went into the ground, seeped down until it reached a layer that would not allow it to penetrate (such a layer is called impermeable), and then water piled up forming a layer that was saturated with water.
In an aquifer, water occupies open space (pore space) that lies between rock particles. This layer would spread out, eventually coming to be under most of the Martian surface. The top of this layer is called the water table. Calculations show that the water table on Mars was for a time 600 meters below the surface.
Several prominent features on the planet have been produced by the action of groundwater. When water rose to the surface or near the surface, various minerals were deposited and sediments became cemented together. Some of the minerals were sulfates that were probably produced when water dissolved sulfur from underground rocks, and then became oxidized when it came into contact with the air. While traveling through the aquifer, the water passed through the igneous rock basalt, which would have contained sulfur. Read more...
Olympia Undae is a vast dune field in the north polar region of the planet Mars. It consists of a broad "sand sea" or erg that partly rings the north polar plateau (Planum Boreum) from about 120° to 240°E longitude and 78° to 83°N latitude. Stretching about 1,100 km (680 mi) across and covering an area of 470,000 km2, Olympia Undae is the largest continuous dune field on Mars. It is similar in size to the Rub' Al Khali in the Arabian Peninsula, the largest active erg on Earth.
Olympia Undae lies within the informally named Borealis basin (also called the north polar basin), the largest of three topographic basins that occur in the northern lowlands of Mars. The average elevation in Olympia Undae is about 4,250 m below datum (martian "sea" level). The 19-km-diameter crater Jojutla lies near the geographic center of Olympia Undae at 81.63°N latitude and 169.65°E longitude.This crater was named by Andres Eloy Martinez Rojas, Mexican astronomer and science writer.
Unda (pl. undae) is a Latin term meaning water, particularly water in motion as waves. The International Astronomical Union (IAU) adopted the term to describe "undulatory," dune-like features on other planets. Olympia Undae contains a variety of dune forms and wind-related (aeolian) depositional features, including sand sheets, transverse dunes, simple barchan dunes, mega-barchans, and complex barchanoid ridges. All of these dune types occur on Earth too. Read more...
A sub-Earth is a planet "substantially less massive" than Earth and Venus. In the Solar System, this category includes Mercury and Mars. Sub-Earth exoplanets are among the most difficult type to detect because their small sizes and masses produce the weakest signal. Despite the difficulty, one of the first exoplanets found was a sub-Earth around a millisecond pulsar PSR B1257+12. The smallest known is WD 1145+017 b with a size of 0.15 Earth radii, or somewhat smaller than Pluto. However, WD 1145+017 b is a dwarf planet as it orbits within a cloud of dust and gas.
The Kepler space telescope opened the realm of sub-Earths by its discovery of them. On January 10, 2012, Kepler discovered the first three sub-Earths around an ordinary star, Kepler-42. As of June 2014, Kepler has 45 confirmed planets that are smaller than Earth, with 17 of them being smaller than 0.8 Rⴲ. In addition, there are over 310 planet candidates with an estimated radius of <1Rⴲ, with 135 of them being smaller than 0.8 Rⴲ.
Sub-Earths commonly lack substantial atmospheres because of their low gravity and weak magnetic fields, allowing stellar radiation to wear away their atmospheres. Due to their small sizes, and unless there are significant tidal forces when orbiting close to the parent star, sub-Earths also have short periods of geologic activity. Read more...
Artist's conception of the Curiosity rover vaporizing rock on Mars. The rover landed on Mars in August 2012.
A Mars rover is a motor vehicle that propels itself across the surface of the planet Mars upon arrival. Rovers have several advantages over stationary landers: they examine more territory, and they can be directed to interesting features, they can place themselves in sunny positions to weather winter months, and they can advance the knowledge of how to perform very remote robotic vehicle control.
There have been six successful robotically operated Mars rovers. The Jet Propulsion Laboratory managed the Mars Pathfinder mission and its now inactive Sojourner rover. It currently manages the Mars Exploration Rover mission's active Opportunity rover and inactive Spirit, and, as part of the Mars Science Laboratory mission, the Curiosity rover.
On January 24, 2016 NASA reported that current studies on Mars by the Curiosity and Opportunity rovers would be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic, and/or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on Mars is now a primary NASA objective. Since June 2018, the Opportunity rover has been out of contact after going into hibernation mode in a dust storm. NASA has stated they are unsure if they will ever be able to regain contact.
Mars 2, Mars 3 and Beagle 2 were physically tethered probes; Sojourner was dependent on the Mars Pathfinder base station for communication with Earth; MER-A & B and Curiosity were on their own. Of these MER-B (Opportunity) and Curiosity are still active, and MER-A (Spirit) and Sojourner completed their missions before losing contact in 2010 and 1997 respectively. Read more...
Branched valley network in Thaumasia quadrangle, as seen by Viking Orbiter. Field of view is roughly 200 km across.
Valley networks are branching networks of valleys on Mars that superficially resemble terrestrial river drainage basins. They are found mainly incised into the terrain of the martian southern highlands, and are typically - though not always - of Noachian age (approximately four billion years old). The individual valleys are typically less than 5 kilometers wide, though they may extend for up to hundreds or even thousands of kilometers across the martian surface.
The form, distribution, and implied evolution of the valley networks are of great importance for what they may tell us about the history of liquid water on the martian surface, and hence Mars' climate history. Some authors have argued that the properties of the networks demand that a hydrological cycle must have been active on ancient Mars, though this remains contentious. Objections chiefly arise from repeated results from models of martian paleoclimate suggesting high enough temperatures and pressures to sustain liquid water on the surface have not ever been possible on Mars.
The advent of very high resolution images of the surface from the HiRISE, THEMIS and Context (CTX) satellite cameras as well as the Mars Orbital Laser Altimeter (MOLA) digital terrain models have drastically improved our understanding of the networks in the last decade. Read more...
Hubble's sharpest view of Mars: Although the ACS fastie finger intrudes it achieved a spatial scale of 5 miles, or 8 kilometres per pixel at full resolution.
The recorded history of observation of the planet Mars dates back to the era of the ancient Egyptian astronomers in the 2nd millennium BCE. Chinese records about the motions of Mars appeared before the founding of the Zhou Dynasty (1045 BCE). Detailed observations of the position of Mars were made by Babylonian astronomers who developed arithmetic techniques to predict the future position of the planet. The ancient Greek philosophers and Hellenistic astronomers developed a geocentric model to explain the planet's motions. Measurements of Mars' angular diameter can be found in ancient Greek and Indian texts. In the 16th century, Nicolaus Copernicus proposed a heliocentric model for the Solar System in which the planets follow circular orbits about the Sun. This was revised by Johannes Kepler, yielding an elliptic orbit for Mars that more accurately fitted the observational data.
The first telescopic observation of Mars was by Galileo Galilei in 1610. Within a century, astronomers discovered distinct albedo features on the planet, including the dark patch Syrtis Major Planum and polar ice caps. They were able to determine the planet's rotation period and axial tilt. These observations were primarily made during the time intervals when the planet was located in opposition to the Sun, at which points Mars made its closest approaches to the Earth.
Better telescopes developed early in the 19th century allowed permanent Martian albedo features to be mapped in detail. The first crude map of Mars was published in 1840, followed by more refined maps from 1877 onward. When astronomers mistakenly thought they had detected the spectroscopic signature of water in the Martian atmosphere, the idea of life on Mars became popularized among the public. Percival Lowell believed he could see a network of artificial canals on Mars. These linear features later proved to be an optical illusion, and the atmosphere was found to be too thin to support an Earth-like environment. Read more...
Artist concept showing sand-laden jets erupting from Martian geysers. (Published by NASA; artist: Ron Miller.)
Martian geysers (or CO
2 jets) are putative sites of small gas and dust eruptions that occur in the south polar region of Mars during the spring thaw. "Dark dune spots" and "spiders" – or araneiforms – are the two most visible types of features ascribed to these eruptions.
They are unlike any terrestrial geological phenomenon. The reflectance (albedo), shapes and unusual spider appearance of these features have stimulated a variety of hypotheses about their origin, ranging from differences in frosting reflectance, to explanations involving biological processes. However, all current geophysical models assume some sort of jet or geyser-like activity on Mars. Their characteristics, and the process of their formation, are still a matter of debate.
These features are unique to the south polar region of Mars in an area informally called the 'cryptic region', at latitudes 60° to 80° south and longitudes 150°W to 310°W; this 1 meter deep carbon dioxide (CO2) ice transition area—between the scarps of the thick polar ice layer and the permafrost—is where clusters of the apparent geyser systems are located. Read more...
Kasei Valles, seen in MOLA elevation data. Flow was from bottom left to right. North is up. Image is approx. 1,600 km (990 mi) across. The channel system extends another 1,200 km (750 mi) south of this image to Echus Chasma.
Outflow channels are extremely long, wide swathes of scoured ground on Mars, commonly containing the streamlined remnants of pre-existing topography and other linear erosive features indicating sculpting by fluids moving downslope. Channels extend many hundreds of kilometers in length and are typically greater than one kilometer in width; the largest valley (Kasei Vallis) is around 3,500 km (2,200 mi) long, greater than 400 km (250 mi) wide and exceeds 2.5 km (1.6 mi) in depth cut into the surrounding plains. These features tend to appear fully sized at fractures in the Martian surface, either from chaos terrains or from canyon systems or other tectonically controlled, deep graben, though there are exceptions. Besides their exceptional size, the channels are also characterized by low sinuosities and high width:depth ratios compared both to other Martian valley features and to terrestrial river channels. Crater counts indicate that most of the channels were cut since the early Hesperian, though the age of the features is variable between different regions of Mars. Some outflow channels in the Amazonis and Elysium Planitiae regions have yielded ages of only tens of million years, extremely young by the standards of Martian topographic features.
On the basis of their geomorphology, locations and sources, the channels are today generally thought to have been carved by outburst floods (huge, rare, episodic floods of liquid water), although some authors still make the case for formation by the action of glaciers, lava, or debris flows. Calculations indicate that the volumes of water required to cut such channels at least equal and most likely exceed by several orders of magnitude the present discharges of the largest terrestrial rivers, and are probably comparable to the largest floods known to have ever occurred on Earth (e.g., those that cut the Channeled Scablands in North America or those released during the re-flooding of the Mediterranean basin at the end of the Messinian Salinity Crisis). Such exceptional flow rates and the implied associated volumes of water released could not be sourced by precipitation but rather demand the release of water from some long-term store, probably a subsurface aquifer sealed by ice and subsequently breached by meteorite impact or igneous activity.
The outflow channels contrast with the Martian channel features known as "valley networks", which much more closely resemble the dendritic planform more typical of terrestrial river drainage basins. Read more...
Did you know...
- ... that Mars' gravity is affected by many negative free air gravity anomalies on its surface?
- ... that the song "Up in the Air" by Thirty Seconds to Mars premiered from the International Space Station in March 2013?
- ... that Rupes Tenuis, the Martian north polar scarp, may have been in retreat since the Late Amazonian period?
- ... that the extended play To the Edge of the Earth by Thirty Seconds to Mars was conceived to raise public awareness of global warming and green politics?
- ... that the Martian dunes of Aspledon Undae may have formed due to erosion of part of the Planum Boreum?
- ... that the Nili Patera dune field was the first location on Mars where evidence was obtained of dune movement of a minimum of 1 metre (3 ft 3 in)?
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Selected images
Composition of "Yellowknife Bay" rocks. Rock veins are higher in calcium and sulfur than "portage" soil (Curiosity, APXS, 2013).
Detection of impact glass deposits (green spots) at Alga crater, a possible site for preserved ancient life
Viking 1 lander's sampling arm scooped up soil samples for tests (Chryse Planitia)
Viking 1 image of Olympus Mons. The volcano and related terrain are approximately 550 km (340 mi) across.
Geologic map of Mars (USGS, 2014)
Photomicrograph by Opportunity showing a gray hematite concretion, nicknamed "blueberries", indicative of the past existence of liquid water
A MOLA-based topographic map showing highlands (red and orange) dominating the southern hemisphere of Mars, lowlands (blue) the northern. Volcanic plateaus delimit regions of the northern plains, whereas the highlands are punctuated by several large impact basins.
Location of subsurface water in Planum Australe
Exposure of silica-rich dust uncovered by the Spirit rover
Potential sources and sinks of methane (CH
4) on MarsGalileo Galilei, first person to see Mars via telescope in 1610.
The tenuous atmosphere of Mars visible on the horizon
In the news
- 25 October 2018 – Climate of Mars
- A new study finds that water on Mars may contain more oxygen than previously thought. (Times Now News)
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