Dark dune spot

Dark Dune Spots are Martian features that can be seen in (mainly the southern) polar region (between 60°-80° latitudes) of the planet on and under the polar icesheet. The spots were discovered on the photos of the Mars Global Surveyor in 1998-99.

They appear at the beginning of the Martian spring, on the dune fields located within craters and covered with ice, mainly at the ridges and slopes of the dunes. By the beginning of the winter, they disappear. As the first years' surveillance shows, next Martian year 70% of the spots appear at the same place. The spots at first seem to be grey, but later their centers darken, becoming black. Their shape is round, with a concentrical structure, on the slopes it's usually elongated, sometimes with streams, possibly of water, that accumulates in pools at the bottom of the dunes.

Possible biological origin

A theory of the spots' possible biological origin is made by a team led by Hungarian astronomer András Horváth and biologists Tibor Gánti and Eörs Szathmáry. The Hungarian team propose that the spots are colonies of photosynthetic Martian microorganisms, which over-winter beneath the ice cap. As the Sun returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesise and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When it has completely melted, they rapidly desiccate and turn black surrounded by a grey aureole.

NASA's current theory is that the patches are composed of either basaltic ash fragments or aggregates of a minor, dark dust component of the layered deposits that forms as a sublimation residue. [ cite journal|title=SURFACE PROPERTIES OF MARS’ POLAR LAYERED DEPOSITS AND POLAR LANDING SITES.|journal=NASA|date=1999|first=A.|last=Vasavada|coauthors=K. E. Herkenhoff|volume=|issue=|pages=|id= |url=http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6086.pdf|format=|accessdate=2008-08-21 ]

References

ee also

*Life on Mars

External links

* [http://www.esa.int/esaCP/ASE4YZ9KOYC_FeatureWeek_0.html Martian spots warrant a close look] - [http://www.esa.int/ ESA Portal]
* [http://www.monochrom.at/dark-dune-spots/ Audio interview about "Dark Dune Spots"]
* Gánti, T. et al, [http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1134.pdf "Evidence For Water by Mars Odyssey is Compatible with a Biogenic DDS-Formation Process"] . (PDF) Lunar and Planetary Science Conference XXXVI (2003)
* Horváth, A., et al, [http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1128.pdf "Annual Change ofMartian DDS-Seepages"] . (PDF) Lunar and Planetary Science Conference XXXVI (2005).