Maunder (Martian crater)

Maunder Crater

Maunder Crater, as seen by HiRISE. The overhang is part of the degraded south (toward bottom) wall of crater. The scale bar is 500 meters long.
Planet Mars
Coordinates 50°00′S 358°30′W / 50°S 358.5°W / -50; -358.5Coordinates: 50°00′S 358°30′W / 50°S 358.5°W / -50; -358.5
Diameter 107.5 km
Eponym Edward W.Maunder, British astronomer (1851-1928)

Maunder Crater is an old, eroded crater in the Noachis quadrangle of Mars, located at 50 South and 358.5 West. It is 107.5 km in diameter and was named after Edward W.Maunder, a British astronomer (1851-1928).[1]

Gullies in Maunder Crater

Martian gullies are small, incised networks of narrow channels and their associated downslope sediment deposits, found on the planet of Mars. They are named for their resemblance to terrestrial gullies. First discovered on images from Mars Global Surveyor, they occur on steep slopes, especially on the walls of craters. Usually, each gully has a dendritic alcove at its head, a fan-shaped apron at its base, and a single thread of incised channel linking the two, giving the whole gully an hourglass shape.[2] They are believed to be relatively young because they have few, if any craters. A subclass of gullies is also found cut into the faces of sand dunes which themselves considered to be quite young. On the basis of their form, aspects, positions, and location amongst and 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] With more repeated observations, more and more changes have been found; since the changes occur in the winter and spring, experts are tending 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] In some years frost, perhaps as thick as 1 meter,

Dunes

When there are perfect conditions for producing sand dunes, steady wind in one direction and just enough sand, a barchan sand dune forms. Barchans have a gentle slope on the wind side and a much steeper slope on the lee side where horns or a notch often forms.[11] The whole dune may appear to move with the wind. Observing dunes on Mars can tell us how strong the winds are, as well as their direction. If pictures are taken at regular intervals, one may see changes in the dunes or possibly in ripples on the dune’s surface. On Mars dunes are often dark in color because they were formed from the common, volcanic rock basalt. In the dry environment, dark minerals in basalt, like olivine and pyroxene, do not break down as they do on Earth. Although rare, some dark sand is found on Hawaii which also has many volcanoes discharging basalt. Barchan is a Russian term because this type of dune was first seen in the desert regions of Turkistan.[12] Some of the wind on Mars is created when the dry ice at the poles is heated in the spring. At that time, the solid carbon dioxide (dry ice) sublimates or changes directly to a gas and rushes away at high speeds. Each Martian year 30% of the carbon dioxide in the atmosphere freezes out and covers the pole that is experiencing winter, so there is a great potential for strong winds.[13]

Why are Craters important?

The density of impact craters is used to determine the surface ages of Mars and other solar system bodies.[14] The older the surface, the more craters present. Crater shapes can reveal the presence of ground ice.

The area around craters may be rich in minerals. On Mars, heat from the impact melts ice in the ground. Water from the melting ice dissolves minerals, and then deposits them in cracks or faults that were produced with the impact. This process, called hydrothermal alteration, is a major way in which ore deposits are produced. The area around Martian craters may be rich in useful ores for the future colonization of Mars.[15] Studies on the earth have documented that cracks are produced and that secondary minerals veins are deposited in the cracks.[16][17][18] Images from satellites orbiting Mars have detected cracks near impact craters.[19] Great amounts of heat are produced during impacts. The area around a large impact may take hundreds of thousands of years to cool.[20][21][22] Many craters once contained lakes.[23][24][25] Because some crater floors show deltas, we know that water had to be present for some time. Dozens of deltas have been spotted on Mars.[26] Deltas form when sediment is washed in from a stream entering a quiet body of water. It takes a bit of time to form a delta, so the presence of a delta is exciting; it means water was there for a time, maybe for many years. Primitive organisms may have developed in such lakes; hence, some craters may be prime targets for the search for evidence of life on the Red Planet.[27]

See also

References

  1. ↑ http://planetarynames.wr.usgs.gov/
  2. 1 2 Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.
  3. ↑ Malin, M., K. Edgett, L. Posiolova, S. McColley, E. Dobrea. 2006. Present-day impact cratering rate and contemporary gully activity on Mars. Science 314, 1573_1577.
  4. ↑ Kolb, et al. 2010. Investigating gully flow emplacement mechanisms using apex slopes. Icarus 2008, 132-142.
  5. ↑ McEwen, A. et al. 2007. A closer look at water-related geological activity on Mars. Science 317, 1706-1708.
  6. ↑ Pelletier, J., et al. 2008. Recent bright gully deposits on Mars wet or dry flow? Geology 36, 211-214.
  7. ↑ NASA/Jet Propulsion Laboratory. "NASA orbiter finds new gully channel on Mars." ScienceDaily. ScienceDaily, 22 March 2014. www.sciencedaily.com/releases/2014/03/140322094409.htm
  8. ↑ http://www.jpl.nasa.gov/news/news.php?release=2014-226
  9. ↑ http://hirise.lpl.arizona.edu/ESP_032078_1420
  10. ↑ http://www.space.com/26534-mars-gullies-dry-ice.html?cmpid=557882
  11. ↑ Pye, Kenneth; Haim Tsoar (2008). Aeolian Sand and Sand Dunes. Springer. p. 138. ISBN 9783540859109.
  12. ↑ http://www.britannica.com/EBchecked/topic/53068/barchan
  13. ↑ Mellon, J. T.; Feldman, W. C.; Prettyman, T. H. (2003). "The presence and stability of ground ice in the southern hemisphere of Mars". Icarus 169 (2): 324–340. Bibcode:2004Icar..169..324M. doi:10.1016/j.icarus.2003.10.022.
  14. ↑ http://www.lpi.usra.edu/publications/slidesets/stones/
  15. ↑ http://www.indiana.edu/~sierra/papers/2003/Patterson.html.
  16. ↑ Osinski, G, J. Spray, and P. Lee. 2001. Impact-induced hydrothermal activity within the Haughton impact structure, arctic Canada: Generation of a transient, warm, wet oasis. Meteoritics & Planetary Science: 36. 731-745
  17. ↑ http://www.ingentaconnect.com/content/arizona/maps/2005/00000040/00000012/art00007
  18. ↑ Pirajno, F. 2000. Ore Deposits and Mantle Plumes. Kluwer Academic Publishers. Dordrecht, The Netherlands
  19. ↑ Head, J. and J. Mustard. 2006. Breccia Dikes and Crater-Related Faults in Impact Craters on Mars: Erosion and Exposure on the Floor of a 75-km Diameter Crater at the Dichotomy Boundary. Special Issue on Role of Volatiles and Atmospheres on Martian Impact Craters Meteoritics & Planetary Science
  20. ↑ name="news.discovery.com"
  21. ↑ Segura, T, O. Toon, A. Colaprete, K. Zahnle. 2001. Effects of Large Impacts on Mars: Implications for River Formation. American Astronomical Society, DPS meeting#33, #19.08
  22. ↑ Segura, T, O. Toon, A. Colaprete, K. Zahnle. 2002. Environmental Effects of Large Impacts on Mars. Science: 298, 1977-1980.
  23. ↑ Cabrol, N. and E. Grin. 2001. The Evolution of Lacustrine Environments on Mars: Is Mars Only Hydrologically Dormant? Icarus: 149, 291-328.
  24. ↑ Fassett, C. and J. Head. 2008. Open-basin lakes on Mars: Distribution and implications for Noachian surface and subsurface hydrology. Icarus: 198, 37-56.
  25. ↑ Fassett, C. and J. Head. 2008. Open-basin lakes on Mars: Implications of valley network lakes for the nature of Noachian hydrology.
  26. ↑ Wilson, J. A. Grant and A. Howard. 2013. INVENTORY OF EQUATORIAL ALLUVIAL FANS AND DELTAS ON MARS. 44th Lunar and Planetary Science Conference.
  27. ↑ Newsom H. , Hagerty J., Thorsos I. 2001. Location and sampling of aqueous and hydrothermal deposits in martian impact craters. Astrobiology: 1, 71-88.
This article is issued from Wikipedia - version of the Tuesday, March 03, 2015. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.