Joly is an

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

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 ...

, located at 74.7°S latitude and 42.7°W longitude in the

Mare Australe quadrangle The Mare Australe quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Mare Australe quadrangle is also referred to as MC-30 (Mars Chart-30). The quadr ...

. It measures 79.9 kilometers in diameter and was named after Irish physicist

John Joly John Joly FRS (1 November 1857 – 8 December 1933) was an Irish physicist and professor of geology at the University of Dublin, known for his development of radiotherapy in the treatment of cancer. He is also known for developing techniques to ...

(1857–1933). The name was approved in 1973, by the International Astronomical Union (IAU)

Working Group for Planetary System Nomenclature 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, outreach ...

(WGPSN).

Spiders

During the winter, much frost accumulates. It freezes out directly onto the surface of the permanent polar cap, which is made of water ice covered with layers of dust and sand. The deposit begins as a layer of dusty CO2 frost. Over the winter, it recrystallizes and becomes denser. The dust and sand particles caught in the frost slowly sink. By the time temperatures rise in the spring, the frost layer has become a slab of semi-transparent ice about 3 feet thick, lying on a substrate of dark sand and dust. This dark material absorbs light and causes the ice to sublimate (turn directly into a gas) Eventually much gas accumulates and becomes pressurized. When it finds a weak spot, the gas escapes and blows out the dust. Speeds can reach 100 miles per hour. Dark channels can sometimes be seen; they are called "spiders." The surface appears covered with dark spots when this process is occurring. Many ideas have been advanced to explain these features. These features can be seen in some of the pictures below. Wikijolywest.jpg, West side of Joly (crater), as seen by CTX camera (on

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 ...

). Wikijolywestspiders.jpg, Dark spots and "spiders" in Joly crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). "Spiders" appear as fuzzy spots; they are where dark dust is accumulating in channels below clear slabs of frozen carbon dioxide. Note: this is an enlargement of the previous image of Joly crater. Wikijolyeskers.jpg, Eskers in Joly crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Eskers are the ridges in the image; they are formed by streams running under a glacier.

References

{{Geography of Mars Mare Australe quadrangle Impact craters on Mars

Spiders

See also

References