Yardangs are common in some regions on Mars, especially in the Medusae Fossae Formation. This formation is found in the Amazonis quadrangle and near the equator. They are formed by the action of wind on sand sized particles; hence they often point in the prevailing direction that the winds were blowing when they were formed. Because they exhibit very few impact craters they are believed to be relatively young. The easily eroded nature of the Medusae Fossae Formation suggests that it is composed of weakly cemented particles, and was most likely formed by the deposition of wind-blown dust or volcanic ash. Yardangs are parts of rock that have been sand blasted into long, skinny ridges by bouncing sand particles blowing in the wind. Layers are seen in parts of the formation. A resistant caprock on the top of yardangs has been observed in Viking, Mars Global Surveyor, and HiRISE photos. Images from spacecraft show that they have different degrees of hardness probably because of significant variations in the physical properties, composition, particle size, and/or cementation.

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File:Medusae Fossae Formation.jpg|Medusae Fossae Formation as seen with Mars Odyssey's THEMIS. Notice elongated formations called yardangs.
WikiESP 035295 1885yardangstop.jpg|Yardangs of various sizes, as seen by HiRISE under HiWish program.
WikiESP 039563 1730yardangs.jpg|Yardangs formed in light-toned material and surrounded by dark, volcanic basalt sand, as seen by HiRISE under HiWish program.
WikiESP 039563 1730yardangsclose.jpg|Close-up image of yardangs, as seen by HiRISE under HiWish program. Arrows point to transverse aeolian ridges, a type of dune..
WikiESP 036429 1925yardangscrater.jpg|Yardangs near a crater, as seen by HiRISE under HiWish program Location is in the Amazonis quadrangle.
WikiESP 035558 1830yardang.jpg|Yardangs, as seen by HiRISE under HiWish program Location is near Gordii Dorsum in the Amazonis quadrangle. These yardangs are in the upper member of the Medusae Fossae Formation.
35558 1830yardangs.jpg|Yardangs, as seen by HiRISE under HiWish program Location is near Gordii Dorsum in the Amazonis quadrangle. Note: this is an enlargement of previous image.
35558 1830yardangsclose.jpg|Yardangs, as seen by HiRISE under HiWish program Location is near Gordii Dorsum in the Amazonis quadrangle. Note: this is an enlargement of previous image.

Wikiesp036510 1735layersyardang.jpg|Yardangs showing layers, as seen by HiRISE under HiWish program Location is Aeolis quadrangle. Read more...

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...

Cerberus is a large "dark spot" (an albedo feature) located on Mars and named after the mythical dog Cerberus. The arcuate markings in the upper right are in the Amazonis plains and may be sand drifts. The Elysium volcano, a yellow area north of Cerberus, has several channels radiating from its flanks. The three bright spots, upper left, are volcanoes partially veiled by thin clouds.

High resolution images show the bulk of the Cerberus Plains is covered by platy-ridged and inflated lavas, which are interpreted as insulated sheet flows. Eastern Cerberus Plains lavas originate at Cerberus Fossae fissures and shields. Some flows extend for 2000 km through Marte Valles into Amazonis Planitia. Athabasca Valles are both incised into pristine lavas and embayed by pristine lavas, indicating that Athabascan fluvial events were contemporaneous with volcanic eruptions. Deposits of the Medusae Fossae Formation lie both over and under lavas, suggesting the deposition of the Medusae Fossae Formation was contemporaneous with volcanism. Statistics of small craters indicate lavas in the Western Cerberus Plains may be less than a million years old, but the model isochrons may be unreliable if the small crater population is dominated by secondary craters. Images showing no large craters with diameters 500 m superimposed on Western Cerberus Plains lavas indicate the same surface is younger than 49 Ma. Read more...

The gravity of Mars is a natural phenomenon, due to the law of gravity, or gravitation, by which all things with mass around the planet Mars are brought towards it. It is weaker than Earth's gravity due to the planet's smaller mass. The average gravitational acceleration on Mars is 3.72076 ms⁻² (about 38% of that of Earth) and it varies laterally. In general, topography-controlled isostasy drives the short wavelength free-air gravity anomalies. At the same time, convective flow and finite strength of the mantle lead to long-wavelength planetary-scale free-air gravity anomalies over the entire planet. Variation in crustal thickness, magmatic and volcanic activities, impact-induced Moho-uplift, seasonal variation of polar ice caps, atmospheric mass variation and variation of porosity of the crust could also correlate to the lateral variations. Over the years models consisting of an increasing but limited number of spherical harmonics have been produced. Maps produced have included free-air gravity anomaly, Bouguer gravity anomaly, and crustal thickness. In some areas of Mars there is a correlation between gravity anomalies and topography. Given the known topography, higher resolution gravity field can be inferred. Tidal deformation of Mars by the Sun or Phobos can be measured by its gravity. This reveals how stiff the interior is, and shows that the core is partially liquid.
The study of surface gravity of Mars can therefore yield information about different features and provide beneficial information for future landing projects. Read more...

A flag of Mars is a flag or flag design that represents the planet Mars or that represents a fictional Martian government. Science fiction authors have, for literary purposes, described the flags of fictional Martian governments. Some of the readers of those flag descriptions have created flags or flag images that are based on the authors’ descriptions. Flag images for two fictional Martian governments are presented in this article.

Advocates of the exploration and settlement of Mars have designed, manufactured, and sold Mars flags, sometimes with the hope that their designs may one day be adopted and used by real Martian governments. The most widely recognized flag of Mars was designed in 1998 by a planetary scientist named Pascal Lee. The Mars Society has manufactured and sold flags based on Lee’s design. Read more...

This is a list of craters on Mars. Impact craters on Mars larger than 1 km exist by the hundreds of thousands, but only about one thousand of them have names. Names are assigned by the International Astronomical Union after petitioning by relevant scientists, and in general, only craters that have a significant research interest are given names. Martian craters are named after famous scientists and science fiction authors, or if less than 60 km in diameter, after towns on Earth. Craters cannot be named for living people, and names for small craters are rarely intended to commemorate a specific town. Latitude and longitude are given as planetographic coordinates with west longitude. Read more...

The Mars ocean hypothesis states that nearly a third of the surface of Mars was covered by an ocean of liquid water early in the planet’s geologic history. This primordial ocean, dubbed Paleo-Ocean and Oceanus Borealis, would have filled the basin Vastitas Borealis in the northern hemisphere, a region which lies 4–5 km (2.5–3 miles) below the mean planetary elevation, at a time period of approximately 4.1–3.8 billion years ago. Evidence for this ocean includes geographic features resembling ancient shorelines, and the chemical properties of the Martian soil and atmosphere. Early Mars would have required a denser atmosphere and warmer climate to allow liquid water to remain at the surface. Read more...

Tempe Terra is a heavily cratered highland region in the northern hemisphere of the planet Mars. Located at the northeastern edge of the Tharsis volcanic province, Tempe Terra is notable for its high degree of crustal fracturing and deformation. The region also contains a large number of small shield volcanoes, lava flows, and other volcanic structures.

The region is named after the albedo feature Tempe, first used by astronomer E.M. Antoniadi in 1930 to describe a bright patch of terrain centered near 40°N, 70°W. The name comes from the Vale of Tempe, a valley located south of Mount Olympus and celebrated by the ancient Greeks for its beauty. The International Astronomical Union (IAU) formally designated the region Tempe Terra in 1979. Terra (pl. terrae) is a Latin descriptor term used in planetary geology for continent-like highland regions (i.e., extensive land masses) on other planets. Read more...

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 and Curiosity are still active, and MER-A and Sojourner completed their missions before losing contact in 2010 and 1997 respectively. Read more...

Martian gullies are small, incised networks of narrow channels and their associated downslope sediment deposits, found on the planet of Mars. They are named for their resemblance to terrestrial gullies. First discovered on images from Mars Global Surveyor, they occur on steep slopes, especially on the walls of craters. Usually, each gully has a dendritic alcove at its head, a fan-shaped apron at its base, and a single thread of incised channel linking the two, giving the whole gully an hourglass shape. They are estimated to be relatively young because they have few, if any craters. A subclass of gullies is also found cut into the faces of sand dunes, that are themselves considered to be quite young. Linear dune gullies are now considered recurrent seasonnal afeatures.

Most gullies occur 30 degrees poleward in each hemisphere, with greater numbers in the southern hemisphere. Some studies have found that gullies occur on slopes that face all directions; others have found that the greater number of gullies are found on poleward facing slopes, especially from 30° to 44° S. Although thousands have been found, they appear to be restricted to only certain areas of the planet. In the northern hemisphere, they have been found in Arcadia Planitia, Tempe Terra, Acidalia Planitia, and Utopia Planitia. In the south, high concentrations are found on the northern edge of Argyre basin, in northern Noachis Terra, and along the walls of the Hellas outflow channels. A recent study examined 54,040 CTX images that covered 85% of the Martian surface found 4861 separate gullied landforms (e.g., individual craters, mounds, valleys, etc.), which totaled tens of thousands of individual gullies. It is estimated that CTX can resolve 95% of gullies.

This article gives a history of the discovery and research on gullies. As research progresses, the cause of Martian gullies has shifted from recent liquid water to pieces of dry ice moving down steep slopes, but research continues. On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers think that the processes carving the gullies involve liquid water. When the volumes of the aprons are compared to the rest of the gully, it appears that there is much less volume in the apron; hence, much of the material may have contained water and ice that disappeared. However, this remains a topic of active research. Because the gullies are so young, this would suggest that liquid water has been present on Mars in its very recent geological past, with consequences for the potential habitability of the modern surface.
On July 10, 2014, NASA reported that gullies on the surface of Mars were mostly formed by the seasonal freezing of carbon dioxide (CO₂), and not by that of liquid water as considered earlier. Read more...

Dark slope streaks are narrow, avalanche-like features common on dust-covered slopes in the equatorial regions of Mars. They form in relatively steep terrain, such as along escarpments and crater walls. Although first recognized in Viking Orbiter images from the late 1970s, dark slope streaks were not studied in detail until higher-resolution images from the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO) spacecraft became available in the late 1990s and 2000s.

The physical process that produces dark slope streaks is still uncertain. They are most likely caused by the mass movement of loose, fine-grained material on oversteepened slopes (i.e., dust avalanches). The avalanching disturbs and removes a bright surface layer of dust to expose a darker substrate. The role that water and other volatiles plays, if any, in streak formation is still debated. Slope streaks are particularly intriguing because they are one of the few geological phenomena that can be observed occurring on Mars in the present day. Read more...

A transit of Phobos across the Sun as seen from Mars takes place when Phobos passes directly between the Sun and a point on the surface of Mars, obscuring a large part of the Sun's disc for an observer on Mars. During a transit, Phobos can be seen from Mars as a large black disc rapidly moving across the face of the Sun. At the same time, the shadow (antumbra) of Phobos moves across the Martian surface.

The event could also be regarded as a particularly quick and shallow annular solar eclipse by Phobos. Read more...

Planum Boreum (Latin: "the northern plain") is the northern polar plain on Mars. It extends northward from roughly 80°N and is centered at . Surrounding the high polar plain is a flat and featureless lowland plain called Vastitas Borealis which extends for approximately 1500 kilometres southwards, dominating the northern hemisphere. Read more...

For a time in the late 19th and early 20th centuries, it was erroneously believed that there were canals on Mars. These were a network of long straight lines in the equatorial regions from 60° north to 60° south latitude on the planet Mars observed by astronomers using early low-resolution telescopes without photography. They were first described by the Italian astronomer Giovanni Schiaparelli during the opposition of 1877, and confirmed by later observers. Schiaparelli called these canali, which was translated into English as "canals". The Irish astronomer Charles E. Burton made some of the earliest drawings of straight-line features on Mars, although his drawings did not match Schiaparelli's. By the early 20th century, improved astronomical observations revealed the "canals" to be an optical illusion, and modern high resolution mapping of the Martian surface by spacecraft shows no such features. Read more...