page_title: Vastitas Borealis
section_title: Surface
hierarchical_section_title: Vastitas Borealis / Surface
caption_attribution_description: Phoenix mission horizon stitched.jpg
context_page_description: Vastitas Borealis is the largest lowland region of Mars. It is in the northerly latitudes of the planet and encircles the northern polar region. Vastitas Borealis is often simply referred to as the northern plains, northern lowlands or the North polar erg of Mars. The plains lie 4–5 km below the mean radius of the planet, and is centered at 87.73°N 32.53°E. To the north lies Planum Boreum. A small part of Vastitas Borealis lies in the Ismenius Lacus quadrangle.
  The region was named by Eugene Antoniadi, who noted the distinct albedo feature of the Northern plains in his book La Planète Mars. The name was officially adopted by the International Astronomical Union in 1973.
  Although it is not an officially recognized feature, the North Polar Basin makes up most of the lowlands in the Northern Hemisphere of Mars. As a result, Vastitas Borealis lies within the North Polar Basin, while Utopia Planitia, another very large basin, is adjacent to it. Some scientists have speculated the plains were covered by a hypothetical ocean at some point in Mars' history and putative shorelines have been suggested for its southern edges.
context_section_description: Unlike some the sites visited by the Viking and Pathfinder landers, nearly all the rocks near the Phoenix landing site on Vastitas Borealis are small.  For about as far as the camera can see, the land is flat, but shaped into polygons.  The polygons are between 2–3 m in diameter and are bounded by troughs that are 20 to 50 cm deep.  These shapes are caused by ice in the soil reacting to major temperature changes. The top of the soil has a crust.  The microscope showed that the soil is composed of flat particles (probably a type of clay) and rounded particles.  When the soil is scooped up, it clumps together.  Although other landers in other places on Mars have seen many ripples and dunes, no ripples or dunes are visible in the area of Phoenix. Ice is present a few inches below the surface in the middle of the polygons.  Along the edge of the polygons the ice is at least 8 inches deep.  When the ice is exposed to the Martian atmosphere it slowly disappears. In the winter there would be accumulations of snow on the surface.
caption: Surface of Mars, as seen by Phoenix.  The ground is shaped into polygons which are common where the ground freezes and thaws.
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