New Rochelle, August 22, 2006 – "Dark spiders" on the surface of Mars might be explained by seasonal temperature changes that melt surface ice and salt, causing erosion, according to a provocative new theory presented in the August 2006 issue (Volume 6, Number 4) issue of Astrobiology, a peer-reviewed journal published by Mary Ann Liebert, Inc. (www.liebertpub.com). Dark spiders are morphological structures characterized by a low-lying region with channels branching away from it. The paper is available free online at www.liebertpub.com/ast.
Olga Prieto-Ballesteros, David Fernández-Remolar, José Antonio Rodríguez-Manfredi, and Susanna Manrubia, from the Center for Astrobiology, National Institute for Aerospace Techniques—Superior Council for Scientific Research, in Madrid Spain, and Franck Selsis, from the Ecole Normale Supérieure de Lyon, France,combined information gathered from recent space probes and evidence-driven hypotheses to devise a model to explain the formation of spiders on the martian surface. They present their proposal in a paper entitled, "Spiders: Water-Driven Erosive Structures in the Southern Hemisphere of Mars."
Recent space missions have yielded images and data to suggest that ongoing climate changes and erosive processes are continuously modifying the surface features of Mars. Visual images from the Mars Orbiter Camera on board the Mars Global Surveyor have revealed spider formations. Documented evidence of cycling climatic changes and the carved branch patterns of the spiders contributed to the authors' model for spider formation.
The first part of the new model agrees with previously proposed models for spider formation: the CO2 ice layer present in the winter is heated in early spring as martian surface temperatures rise and gas emissions from underground spew material from beneath the ice and disperse it over the surface.
The recent seasonal observations, however, require modifications to the prevailing model. In late spring, as the ground temperature continues to increase, the water-ice salt-rich permafrost layer just below the surface melts and re-suspends the dispersed material. This suspension-rich brine is transported to lower areas, and as it drains, the briny water causes erosion. The authors hypothesize that fluid erosion is the main process responsible for the formation of the spider-like channels that radiate out from the crater.
"If the negative topography and radial branching patterns of spiders are due to seasonal periods of liquid erosion, then the spiders are especially intriguing morphological features," says journal Editor-in-Chief, Sherry L. Cady, Ph.D., Associate Professor in the Department of Geology at Portland State University. "Sites that accumulate new aqueous precipitates and sediments each year would be of special interest with regard to evaluating the astrobiological potential of Mars."
Astrobiology is the leading peer-reviewed journal in its field. To promote this developing field, the Journal has teamed up with The Astrobiology Web to highlight one outstanding paper per issue of Astrobiology. This paper is available free online at www.liebertpub.com/ast and to visitors of The Astrobiology Web at www.astrobiology.com.
Astrobiology is published quarterly in print and online. The journal provides a forum for scientists seeking to advance our understanding of life's origins, evolution, distribution and destiny in the universe. A complete table of contents and a full text for this issue may be viewed online at www.liebertpub.com/ast.
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full paper available for readers of Astrobiology.com