Planum Boreum (

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

: "the northern plain") is the northern polar plain on

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

. 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.

Features

The main feature of the Planum Boreum is a large fissure or canyon in the polar ice cap called

Chasma Boreale Chasma Boreale is a large canyon in Mars's north polar ice cap in the Mare Boreum quadrangle of Mars at 83° north latitude and 47.1° west longitude. It is about long and was named after a classical albedo feature name. The canyon's sides rev ...

. It is up to wide and features scarps up to high. By comparison, the

Grand Canyon The Grand Canyon (, yuf-x-yav, Wi:kaʼi:la, , Southern Paiute language: Paxa’uipi, ) is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is long, up to wide and attains a depth of over a m ...

is approximately deep in some places and long but only up to wide. Chasma Boreale cuts through polar deposits and ice, such as those present at

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...

. Planum Boreum interfaces with Vastitas Borealis west of Chasma Boreale at an irregular scarp named

Rupes Tenuis Rupes Tenuis ( la, thin cliff) is a Martian north polar scarp. It is named after one of the classical albedo features on Mars. Its name was officially approved by IAU in 1988. It extends from latitude 74.94°N to 82.2°N and from longitude 242.1 ...

. This scarp reaches heights of up to 1 km. At other places, the interface is a collection of mesas and troughs. Planum Boreum is surrounded by large fields of

sand dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...

s spanning from 75°N to 85°N. These dune fields are named Olympia Undae,

Abalos Undae Abalos Undae (Latin for "Abalos Waves") is a dune field on Mars in the periphery of Planum Boreum, the Martian North pole. It is one of the Classical albedo features on Mars, officially named northern circumpolar dune fields, along with Olympia ...

Siton Undae Siton Undae is one of the largest and densest dune fields in the vicinity of Planum Boreum, the Martian northern polar ice-cap. It is named after one of the classical albedo features on Mars. Its name was officially approved by IAU on 20 March 20 ...

, and

Hyperboreae Undae Hyperboreae Undae ( Latin: "Far Northern Waves/Dunes") is one of the largest and densest dune fields of Planum Boreum, the Martian North Pole. It is named after one of the classical albedo features on Mars. Its name was officially approved by IA ...

. Olympia Undae, by far the largest, covers from 100°E to 240°E. Abalos Undae covers from 261°E to 280°E and Hyperboreale Undae spans from 311°E to 341°E. See also List of extraterrestrial dune fields.

Ice cap

Planum Boreum is home to a permanent

ice cap In glaciology, an ice cap is a mass of ice that covers less than of land area (usually covering a highland area). Larger ice masses covering more than are termed ice sheets. Description Ice caps are not constrained by topographical feat ...

consisting mainly of water ice (with a 1 m thick veneer of carbon dioxide ice during the winter). It has a volume of 1.2 million cubic kilometres and covers an area equivalent to about 1.5 times the size of

Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...

. It has a radius of 600 km. The maximum depth of the cap is 3 km. The spiral troughs in the ice cap are formed by katabatic winds that entrain surface ice eroded from the equator-facing sides of the troughs, likely aided by solar ablation ( sublimation), which is then redeposited on the colder pole-facing slopes. The troughs are roughly perpendicular to the wind direction, which is shifted by the

Coriolis effect In physics, the Coriolis force is an inertial or fictitious force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the ...

, leading to the spiral pattern. The troughs gradually migrate towards the pole over time; the central troughs have moved about 65 km in the last 2 million years.

is a canyon-like feature older than the troughs, and in contrast is aligned parallel to the wind direction. The surface composition of the northern ice cap in middle spring (after a winter's accumulation of seasonal dry ice) has been studied from orbit. The outer edges of the ice cap are contaminated with dust (0.15% by weight) and are mostly water ice. As one moves toward the pole, the surface water ice content decreases and is replaced by dry ice. The purity of the ice also increases. At the pole, the surface seasonal ice consists of essentially pure dry ice with little dust content and 30

parts per million In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, th ...

of water ice. The Phoenix lander, launched in 2007, arrived at Mars in May 2008 and successfully landed in the Vastitas Borealis region of the planet on May 25, 2008. The north polar cap of Mars has been proposed as a landing site for a human Mars expedition by

Geoffrey A. Landis Geoffrey Alan Landis (; born May 28, 1955) is an American aerospace engineer and author, working for the National Aeronautics and Space Administration (NASA) on planetary exploration, interstellar propulsion, solar power and photovoltaics. He h ...

and by Charles Cockell.

Recurring phenomena

Avalanches

A February 2008 HiRISE observation captured four

avalanche An avalanche is a rapid flow of snow down a slope, such as a hill or mountain. Avalanches can be set off spontaneously, by such factors as increased precipitation or snowpack weakening, or by external means such as humans, animals, and ea ...

s in progress off a cliff. The cloud of fine material is across and extends from the base of the cliff. The reddish layers are known to be rock rich in water ice while the white layers are seasonal carbon dioxide frost. The landslide is thought to have originated from the uppermost red layer. Follow-up observations are planned to characterize the nature of the landslide debris.

Repeating annular cloud

A large doughnut-shaped cloud appears in North polar region of Mars around the same time every Martian year and of about the same size.Mars Global Surveyor - "8 Year Anniversary"
/ref> It forms in the morning, dissipates by the Martian afternoon. The outer diameter of the cloud is roughly , and the inner hole or eye is across. The cloud is thought to be composed of water-ice, so it is white in color, unlike the more common dust storms. It looks like a cyclonic storm, similar to hurricane, but it does not rotate. The cloud appears during the northern summer and at high latitude. Speculation is that this is due to unique climate conditions near the northern pole. Cyclone-like storms were first detected during the Viking orbital mapping program, but the northern annular cloud is nearly three times larger. The cloud has also been detected by various probes and telescopes including the Hubble and

Mars Global Surveyor ''Mars Global Surveyor'' (MGS) was an American robotic space probe developed by NASA's Jet Propulsion Laboratory and launched November 1996. MGS was a global mapping mission that examined the entire planet, from the ionosphere down through t ...

. When

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

viewed it in 1999, it was thought to be

cyclonic storm In meteorology, a cyclone () is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above (opposite to an anti ...

. The diameter was measured to be approximately 1750 km, and featured an "eye" 320 km in diameter.

References

External links

Fly over the Chasma Boreale at Martian north pole
- courtesy of Mars Express
Geologic Map of the Northern Plains of MarsHiRISE image of Martian landslidesHiRISE image of permanent ice mound separated from cap
*Various

HiRISE High Resolution Imaging Science Experiment is a camera on board the '' Mars Reconnaissance Orbiter'' which has been orbiting and studying Mars since 2006. The 65 kg (143 lb), US$40 million instrument was built under the direction ...

images of the north polar ice cap

{{Portal bar, Solar System Plains on Mars Mare Boreum quadrangle