Green Valley is a region 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 ...

within

Vastitas Borealis (Latin 'northern waste') 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 ...

that was chosen as the landing site of

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

Phoenix Phoenix most often refers to: * Phoenix (mythology), a legendary bird from ancient Greek folklore * Phoenix, Arizona, a city in the United States Phoenix may also refer to: Mythology Greek mythological figures * Phoenix (son of Amyntor), a ...

lander. It is located at 68.35 degrees north, 233 degrees east. The valley is about 50 kilometres wide but only about 250 metres deep; either it was filled in or was never any deeper than that. The edges are not visible from the middle of the valley.A Green Valley for Phoenix - Planetary News , The Planetary Society
Mars from Phoenix

The name "Green Valley" is not officially recognised by the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

. It came from the decision process by which it was selected as Phoenix's landing site: prospective landing areas were color-coded based on how hazardous they were, with red being most hazardous through yellow to green being the safest. Green Valley has relatively few of the large boulders that could have tipped the lander if it had hit one during touchdown. The ground within Green Valley is covered with polygonal features several metres across and roughly ten centimetres high, thought to be caused either by thermal contraction ( ice-wedge polygons) or by the effects of wind-blown dust (sand-wedge polygons). Water ice is thought to be just below the surface. During the local winter as much as three feet of

carbon dioxide ice Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and sublimates directly from the solid state to the gas state. It is used primarily a ...

is expected to appear on the surface. Shortly before Phoenix's scheduled landing, the

Mars Reconnaissance Orbiter ''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft designed to study the geology and climate of Mars, provide reconnaissance of future landing sites, and relay data from surface missions back to Earth. It was launched on August 12, 2005, an ...

photographed a pair of kilometer-tall

dust devil A dust devil is a strong, well-formed, and relatively short-lived whirlwind. Its size ranges from small (half a metre wide and a few metres tall) to large (more than 10 m wide and more than 1 km tall). The primary vertical motion is u ...

s in the Green Valley area.Dust devils spotted at Mars probe's landing site - space - 7 May 2008 - New Scientist Space
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References

Further reading