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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. In 1999, the Hubble Space Telescope captured a cyclonic storm in the region. The diameter of the storm was approximately 1750 km and featured an eye 320 kilometres in diameter.

Ice cap

Planum Boreum is home to a permanent ice cap comprised mainly of water and carbon dioxide ice. It has a volume of 1.2 million cubic kilometres and covers an area equivalent to about 1.5 times the size of Texasmarker. It has a radius of 600 km. The maximum depth of the cap is 3 km. The spiral patterns in the ice cap were mostly carved by fierce winds and sublimation.

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 comprised mostly of 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 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 polar cap of Mars has been proposed as a landing site for a human Mars expedition by Landis and by Cockell.

Features

Elevation map of the north pole.
Note how Planum Boreum soars above the surrounding featureless terrain.
Click to enlarge and for more info.


The main feature of the Planum Boreum is a large fissure or canyon in the polar ice cap called Chasma Boreale. It is up to 100 km wide and features scarps up to 2 km high. By comparison, the Grand Canyonmarker is approximately 1.6 km deep in some places and 446 km long but only up to 24 km wide. Chasma Boreale cuts through polar deposits and ice, such as those present at Greenlandmarker.

Planum Boreum interfaces with Vastitas Borealis west of Chasma Boreale at an irregular scarp named Rupes Tenuis. 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 dunes spanning from 75°N to 85°N. These dune fields are named Olympia Undae, Abalos Undae and Hyperboreae Undae. 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.

Avalanches



A February 2008 HiRISE observation captured four avalanches in progress off a 700 meter cliff. The cloud of fine material is 180 meters across and extends 190 meters 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.

See also



References

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