Arandas (crater)

Arandas Crater is a crater in the Mare Acidalium quadrangle of Mars, located 42.77° North and 15.17° West. It is 24.76 km (15.39 mi) in diameter and is named after the town of Arandas in Mexico.[1]

Arandas

Arandas Crater, as seen by HiRISE. Click on image for a better view of North and South Walls, as well as central hills. Scale bar is 1000 meters long.
Planet	Mars
Coordinates	42.77°N 15.17°W / 42.77; -15.17
Quadrangle	Mare Acidalium quadrangle
Diameter	24.76 km (15.39 mi)
Eponym	The town of Arandas in Mexico

Viking orbiter mosaic of Arandas crater

Detail of the ejecta of Arandas crater

Gullies are visible in pictures of Arandas. On the basis of their form, aspects, positions, and location amongst an apparent interaction with features thought to be rich in water ice, many researchers believed that the processes carving the gullies involve liquid water. However, this remains a topic of active research. As soon as gullies were discovered,[2] researchers began to image many gullies over and over, looking for possible changes. By 2006, some changes were found.[3] Later, with further analysis it was determined that the changes could have occurred by dry granular flows rather than being driven by flowing water.[4][5][6] With continued observations many more changes were found in Gasa Crater and others.[7] As further observations have been made, still more changes have been noted; since the changes occur in the winter and spring, experts tend to believe that gullies were formed from dry ice. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon-dioxide frost and temperatures that would not have allowed for liquid water. When dry ice frost changes to a gas, it may lubricate dry material to flow, especially on steep slopes.[8][9][10]

• 
  MOLA map showing Arandas Crater and other nearby craters. Color indicates elevation.
• 
  Arandas Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter).
• 
  Gullies in Arandas Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note: this is an enlargement of the previous photo.
• 
  Gullies in Arandas Crater, as seen by HiRISE under HiWish program.

Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits. As craters get larger (greater than 10 km (6.2 mi) in diameter) they usually have a central peak.[11] The peak is caused by a rebound of the crater floor following the impact.[12] Sometimes craters expose layers that were buried. Rocks from deep underground are tossed onto the surface. Hence, craters can expose what lies deep under the surface.