Sedimentary Geology at Meridiani Planum

[JonClarke]

Hi all<br /><br />A major collection of papers about the sediments at Meridiani has just been published. It can be found in: “Earth and Planetary Science Letters” Volume 240, Issue 1, Pages 1-190 (30 November 2005). "Sedimentary Geology at Meridiani Planum, Mars" Edited by Steven W. Squyres and Andrew H. Knoll .<br /><br />There are eight papers in all, I will post the abstracts numbered sequentially. Unfortunately the full papers need subscription via a library.<br /><br />Jon<br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Steven W. Squyres & Andrew H. Knoll "Sedimentary rocks at Meridiani Planum: Origin, diagenesis, and implications for life on Mars". Earth and Planetary Science Letters 240 (2005) 1-10.<br /><br />Abstract: The MER rover Opportunity has carried out the first outcrop-scale investigation of ancient sedimentary rocks on Mars. The rocks, exposed in craters and along fissures in Meridiani Planum, are sandstones formed via the erosion and re-deposition of fine grained siliciclastics and evaporates derived from the chemical weathering of olivine basalts by acidic waters. A stratigraphic section more than seven meters thick measured in Endurance crater is dominated by eolian dune and sand sheet facies; the uppermost half meter, however, exhibits festoon cross lamination at a length scale that indicates subaqueous deposition, likely in a playa-like interdune setting. Silicates and sulfate minerals dominate outcrop geochemistry, but hematite and Fe3D3 (another ferric iron phase) make up as much as 11% of the rocks by weight. Jarosite in the outcrop matrix indicates precipitation at low pH. Cements, hematitic concretions, and crystal molds attest to a complex history of early diagenesis, mediated by ambient ground waters. The depositional and early diagenetic paleoenvironment at Meridiani was arid, acidic, and oxidizing, a characterization that places strong constraints on astrobiologial inference.<br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

J.P. Grotzinger et al. "Stratigraphy and sedimentology of a dry to wet eolian depositional system, Burns formation, Meridiani Planum, Mars." Earth and Planetary Science <br />Letters 240 (2005) 11-72.<br /><br />Abstract: Outcrop exposures of sedimentary rocks at the Opportunity landing site (Meridiani Planum) form a set of genetically related strata defined here informally as the Burns formation. This formation can be subdivided into lower, middle, and upper units which, respectively, represent eolian dune, eolian sand sheet, and mixed eolian sand sheet and interdune facies associations. Collectively, these three units are at least 7 m thick and define a bwetting-upwardQ succession which records a progressive increase in the influence of groundwater and, ultimately, surface water in controlling primary depositional processes. <br /> <br />The Burns lower unit is interpreted as a dry dune field (though grain composition indicates an evaporitic source), whose preserved record of large-scale cross-bedded sandstones indicates either superimposed bedforms of variable size or reactivation of lee-side slip faces by episodic (possibly seasonal) changes in wind direction. The boundary between the lower and middle units is a significant eolian deflation surface. This surface is interpreted to record eolian erosion down to the capillary fringe of the water table, where increased resistance to wind-induced erosion was promoted by increased sediment cohesiveness in the capillary fringe.The overlying Burns middle unit is characterized by fine-scale planar-laminated to low-angle-stratified sandstones. These sandstones accumulated during lateral migration of eolian impact ripples over the flat to gently undulating sand sheet surface. In terrestrial settings, sand sheets may form an intermediate environment between dune fields and interdune or playa surfaces. The contact between the middle and upper units of the Burns formation is interpreted as a diagenetic front, where recrystallizat <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

B.C. Clark, et al. "Chemistry and mineralogy of outcrops at Meridiani Planum." Earth and Planetary Science Letters 240 (2005) 73-94. <br /><br />Abstract: Analyses of outcrops created by the impact craters Endurance, Fram and Eagle reveal the broad lateral continuity of chemical sediments at the Meridiani Planum exploration site on Mars. Approximately ten mineralogical components are implied in these salt-rich silicic sediments, from measurements by instruments on the Opportunity rover. Compositional trends in an apparently intact vertical stratigraphic sequence at the Karatepe West ingress point at Endurance crater are consistent with non-uniform deposition or with subsequent migration of mobile salt components, dominated by sulfates of magnesium. Striking variations in Cl and enrichments of Br, combined with diversity in sulfate species, provide further evidence of episodes during which temperatures, pH, and water to rock ratios underwent significant change. To first order, the sedimentary sequence examined to date is consistent with a uniform reference composition, modified by movement of major sulfates upward and of minor chlorides downward. This reference composition has similarities to martian soils, supplemented by sulfate anion and the alteration products of mafic igneous minerals. Lesser cementation in lower stratigraphic units is reflected in decreased energies for grinding with the Rock Abrasion Tool. Survival of soluble salts in exposed outcrop is most easily explained by absence of episodes of liquid H2O in this region since the time of crater formation.<br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

S.M. McLennan, et al. "Provenance and diagenesis of the evaporite-bearing Burns formation, Meridiani Planum, Mars." Earth and Planetary Science Letters 240 (2005) 95-121.<br /><br />Abstract: Impure reworked evaporitic sandstones, preserved on Meridiani Planum, Mars, are mixtures of roughly equal amounts of altered siliciclastic debris, of basaltic provenance (40 ± 10% by mass), and chemical constituents, dominated by evaporitic minerals (jarosite, Mg-, Ca-sulfates ± chlorides ±Fe-, Na-sulfates), hematite and possibly secondary silica (60 ±10%). These chemical constituents and their relative abundances are not an equilibrium evaporite assemblage and to a substantial degree have been reworked by aeolian and subaqueous transport. Ultimately they formed by evaporation of acidic waters derived from interaction with olivine-bearing basalts and subsequent diagenetic alteration. The rocks experienced an extended diagenetic history, with at least two and up to four distinct episodes of cementation, including stratigraphically restricted zones of recrystallization and secondary porosity, non-randomly distributed, highly spherical millimeter-scale hematitic concretions, millimeter-scale crystal molds, interpreted to have resulted from dissolution of a highly soluble evaporite mineral, elongate to sheet-like vugs and evidence for minor synsedimentary deformation (convolute and contorted bedding, possible teepee structures or salt ridge features). Other features that may be diagenetic, but more likely are associated with relatively recent meteorite impact, are meter-scale fracture patterns, veins and polygonal fractures on rock surfaces that cut across bedding. Crystallization of minerals that originally filled the molds, early cement and sediment deformation occurred syndepositionally or during early diagenesis. All other diagenetic features are consistent with formation during later diagenesis in the phreatic (fluid saturated) zone or capillary fringe of a groundwater table un <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

N.J. Tosca, et al. "Geochemical modeling of evaporation processes on Mars: Insight from the sedimentary record at Meridiani Planum." Earth and Planetary Science Letters 240 (2005) 122-148.<br /><br />Abstract: New data returned from the Mars Exploration Rover (MER) mission have revealed abundant evaporites in the sedimentary record at Meridiani Planum. A working hypothesis for Meridiani evaporite formation involves the evaporation of fluids derived from the weathering of martian basalt and subsequent diagenesis. On Earth, evaporite formation in exclusively basaltic settings is rare. However, models of the evaporation of fluids derived from experimentally weathering synthetic martian basalt provide insight into<br />possible formation mechanisms. The thermodynamic database assembled for this investigation includes both Fe2+ and Fe3+ in Pitzer's ion interaction equations to evaluate Fe redox disequilibrium at Meridiani Planum. Modeling results suggest that evaporation of acidic fluids derived from weathering olivine-bearing basalt should produce Mg, Ca, and Fe-sulfates such as jarosite and melanterite. Calculations that model diagenesis by fluid recharge predict the eventual breakdown of jarosite to goethite as well as the preservation of much of the initial soluble evaporite component at modeled porosity values appropriate for relevant depositional environments (b0.30). While only one of several possible formation scenarios, this simple model is consistent with much of the chemical and mineralogical data obtained on Meridiani Planum outcrop.<br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

David C. Fernández-Remolar,et al. "The Río Tinto Basin, Spain: Mineralogy, sedimentary geobiology, and implications for interpretation of outcrop rocks at Meridiani Planum, Mars." Earth and Planetary Science Letters 240 (2005) 149-167.<br /><br />Abstract: Exploration by the NASA rover Opportunity has revealed sulfate- and hematite-rich sedimentary rocks exposed in craters and other surface features of Meridiani Planum, Mars. Modern, Holocene, and Plio-Pleistocene deposits of the R&#305;´o Tinto, southwestern Spain, provide at least a partial environmental analog to Meridiani Planum rocks, facilitating our understanding of Meridiani mineral precipitation and diagenesis, while informing considerations of martian astrobiology. Oxidation, thought to be biologically mediated, of pyritic ore bodies by groundwaters in the source area of the R&#305;´o Tinto<br />generates headwaters enriched in sulfuric acid and ferric iron. Seasonal evaporation of river water drives precipitation of hydronium jarosite and schwertmannite, while (Mg,Al,Fe3+)-copiapite, coquimbite, gypsum, and other sulfate minerals precipitate nearby as efflorescences where locally variable source waters are brought to the surface by capillary action. During the wet season, hydrolysis of sulfate salts results in the precipitation of nanophase goethite. Holocene and Plio-Pleistocene terraces show increasing goethite crystallinity and then replacement of goethite with hematite through time. Hematite in Meridiani spherules also formed during diagenesis, although whether these replaced precursor goethite or precipitated directly from groundwaters is not known. The retention of jarosite and other soluble sulfate salts suggests that water limited the diagenesis of Meridiani rocks. <br /><br />Diverse prokaryotic and eukaryotic microorganisms inhabit acidic and<br />seasonally dry R&#305;´o Tinto environments. Organic matter does not persist in R&#305;´o Tinto sediments, but biosignatures imparted to s <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

R.V. Morris, et al. "Hematite spherules in basaltic tephra altered under aqueous, acid-sulfate conditions on Mauna Kea volcano, Hawaii: Possible clues for the occurrence of hematite-rich spherules in the Burns formation at Meridiani Planum, Mars." Earth and Planetary Science Letters 240 (2005) 168-178<br /><br />Abstract: Iron-rich spherules (N90% Fe2O3 from electron microprobe analyses) ~10-100 Am in diameter are found within sulfate-rich rocks formed by aqueous, acid-sulfate alteration of basaltic tephra on Mauna Kea volcano, Hawaii. Although some spherules are nearly pure Fe, most have two concentric compositional zones, with the core having a higher Fe/Al ratio than the rim. Oxide totals less than 100% (93-99%) suggest structural H2O and/or OH 1. The transmission Mo¨ssbauer spectrum of a spherule-rich separate is dominated by a hematite (a-Fe2O3) sextet whose peaks are skewed toward zero velocity. Skewing is consistent with Al3+ for Fe3+ substitution and structural H2O and/or OH 1. The grey color of the spherules implies specular hematite. Whole-rock powder X-ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra. Whether spherule formation proceeded directly from basaltic material in one event (dissolution of basaltic material and precipitation of hematite spherules) or whether spherule formation required more than one event (formation of Fe-bearing sulfate rock and subsequent hydrolysis to hematite) is not currently constrained. By analogy, a formation pathway for the hematite spherules in sulfate-rich outcrops at Meridiani Planum on Mars (the Burns formation) is aqueous alteration of basaltic precursor material under acid-sulfate conditions. Although hydrothermal conditions are present on Mauna Kea, such conditions may not be required for spherule formation on Mars if the time interval for hydrolysis at lower tem <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Andrew H. Knoll, et al. "An astrobiological perspective on Meridiani Planum." Earth and Planetary Science Letters 240 (2005) 179-189. <br /><br />Abstract: Sedimentary rocks exposed in the Meridiani Planum region of Mars record aqueous and eolian deposition in ancient dune and interdune playa-like environments that were arid, acidic, and oxidizing. On Earth, microbial populations have repeatedly adapted to low pH and both episodic and chronic water limitation, suggesting that, to a first approximation, the Meridiani plain may have been habitable during at least part of the interval when deposition and early diagenesis took place. On the other hand, the environmental conditions inferred for Meridiani deposition would have posed a challenge for prebiotic chemical reactions thought to have played a role in the origin of life on Earth. Orbital observations suggest that the combination of sulfate minerals and hematite found in Meridiani rocks may be unusual on the martian surface; however, there is reason to believe that acidity, aridity, and oxidizing conditions were broadly distributed on ancient Mars. When these conditions were established and how much environmental heterogeneity existed on early Mars remain to be determined. Because sulfates and iron oxides can preserve detailed geochemical records of environmental history as well as chemical, textural and microfossil signatures of biological activity, Meridiani Planum is an attractive candidate for Mars sample return.<br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[earthseed]

Hi, Jon.<br /><br />Would I be correct in concluding that Meridiani Planum experienced maybe up to four short-lived episodes of shallow water, and nothing after that? No dates were given; I wonder how old these sediments are, and how long the aqueous periods lasted?

 

[rlb2]

Sand dunes in Endurance Eolian flow origins – wind blown dry stuff. <br /><br />What I see here Jon, see images below, unless I missing something is dunes resembling solids. Can dry fine grain material; without a liquid that fill the voids that turn to a solid, with sharp corners, make impressions like this?<br /><br />Note some of the peaks are over 90 degrees perpendicular to and overhang the surface; the second image below almost looks semi-transparent. Also note the yellow looking substance that appears to be seeping out of the dunes at 7:00 O-Clock from the center of the image below???<br /><br />1P146915466EL5M1<br /> <div class="Discussion_UserSignature"> Ron Bennett </div>

 

[rlb2]

1P146915363EL5M1 <div class="Discussion_UserSignature"> Ron Bennett </div>

 

[JonClarke]

Wind can make the most amazingly beautiful abstract shapes, I don't see anything unusual in that image, in terms of morphology, certainly not over steepened faces. The light angle is low, and the shaded slopes are towards the camera, this makes them look steeper than they are. The slopes that are side on are actually quite gentle for dunes, probably less than 30 degrees.<br /><br />However, I agree that the surface of the dunes reflects lightly oddly, there is a distinct sheet to the surface. However, haematite, such as makes up the concretions and are probably present in the small dunes in a significant fraction, can be very reflective under some light angles. I have often seen this phenomenon in lags of haematite granules on earth in the morning and early evening, they can almost look like glass fragments. Add the contrast saturation of the imaging system that results from this and you have this eeriely beautiful result.<br /><br />Not sure what the "yellow" material is, small rippled drifts of a different composition?<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Paper 1 says: "The age of the rocks at Meridiani is difficult to determine. An upper bound can be derived from orbital images that show that the Meridiani plains materials disconformably overlie dissected Middle to late Noachian cratered terrains... The rocks observed by Opportunity therefore could be as old as three to four billion years."<br /><br />As for the number of wet episodes, remember that these papers are based on a 7 m section out of a total stratigraphic thickness that is possibly nearly a kilometer thick. It is extremely unlike that these are the only water laid sediments.<br /><br />As paper 2 shows, even the aeolian sediments are derived from laterally equivalent lakes, rather as the White Sands dunes are. In Australia such complexes of lakes, dunes, and groundwater discharge zones are collectively known as "boinkas" <img src="/images/icons/smile.gif" /><br /><br />I have no idea how long each major unit took to be deposited. In bionkas a few m of sediment may take thousands or even millions of years to accumulate. A lot will depend on the groundwater history. When groundwater is low the lake sediment dry out and deflate to form dunes. When groundwater is high form sediments are trapped or precipitated. Ecventually the sediments are cemented and then can resist further erosion to some degree.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[rlb2]

<font color="orange">I don't see anything unusual in that image, in terms of morphology<font color="white"><br /><br />I haven't been out in the field as much as you have but I have been to the beach and saw similar looking dunes, however I never saw such sharp peaks. Are they some dunes on earth similar to these without being rigid?<br /><br /><font color="orange">Add the contrast saturation of the imaging system that results from this and you have this eeriely beautiful result.<font color="white"><br /><br />Thanks.<br /><br />I add contrast to help sharpen the image so it isn't so fuzzy, like putting glases on to view them. I have to de-saturate the original image a little because most of them are oversaturated.<br /></font></font></font></font> <div class="Discussion_UserSignature"> Ron Bennett </div>

 

[JonClarke]

That is a really valuable paper, very detailed with lots of interesting stuff. I have been meaning to post a link to it, you have to register but it is free. This is the first issue, I hope there will be lopts more interesting stuff in the future.<br /><br />http://marsjournal.org/<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Dunes can be knife sharp if the last sand moving event was depositional and not erosional. I watched the latest version of "Flight of the Phoenix" last night. Not as good as the original film (or the book), but it has some amazing footage of sand dunes in it. I was thinking of this thread as I watched. <img src="/images/icons/smile.gif" /><br /><br />It is not impossible that they are cemented of course, at least weakly. Some of the surfaces that Opportunity has roled over look crusted, this would certainly hep their preservation. It might also explain why the rover has only got bogged once.<br /><br />Polar dunes may well be cemented, OMEGA has seen extensive gypsum in the north polar dune field, plus ice and snow is a possibility, as Mary Bourke and others have suggested.<br /><br />That there is over saturation in this image is certainly consistent with some sort of specular reflection happening. Gypsum too can be highly relfective, if there are gypsum grains in the and this might contribute to it.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[silylene old]

Heh, the dunes in <i>Flight of the Phoenix</i> were cool! I always look for the prevailing wind directions and angle of repose, and also noticed the scene when the winds picked up and streamers of light sands flew up and off the crest (something that probably never happens anymore on Mars). <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[bobw]

Hi Jon. Is it a full moon? When I google equilibrium evaporite assemblage and isotropic hydrological conditions the first link is to here. After I quit reading isotropic as isotonic I think I figgured that one out but I sure would appreciate an explaination of "not an equilibrium evaporite assemblage and to a substantial degree have been reworked by aeolian and subaqueous transport", please. I found this, which seems to say that it is possible to predict how much and what evaporites will form. I <i>think</i> this is the kind of thing your #4 is about; sort of like yield percentages in chemistry.<br /><br />http://www.boulder.swri.edu/~bullock/Homedocs/LPSC1998JMM.pdf<br />____________<br />T o generate brines, samples of unaltered mineral mixtures, which are thought to represent the rock in the upper martian crust were ground and mixed with water. Individual pristine minerals were used to simulate martian rocks and have been chosen on the basis of SNC meteorite mineralogy [6]. The slurries were placed in an environment (pressure 1 bar, temperatures set a several values: 1°, 30°, and 50° C) which represent the conditions within the martian subsurface where brines might reside.<br /><br />Evaporite Analysis. For the brines studies, approximately 80 g aliquots of liquid will be used in chemical analyses of the dissolved ion load. The solute load will be tracked over time, and is expected eventually to stabilize for most ions. For evaporite analysis, the remaining 20 g of brine will be divided into four aliquots, and desiccated under simulated Mars atmosphere in one of four ways. These are: Evaporation, rapid and slow, and freezing rapid and slow. Based on pilot-run experience, we calculate that we will have a significant fraction of a milligram of evaporites to analyze. The mineral suites will be examined by infrared spectroscopy as well as by electron microscopy and powder X-ray d <div class="Discussion_UserSignature"> </div>

 

[bobw]

I will try to rephrase that question.<br /><br />Do the crystals in an evaporite deposit have to remain exactly where they were formed to be an equilibrium assemblage or can they blow around in the bottom of a crater and remain dry and still be an equilibrium assemblage?<br /><br />If they got wet with distilled water and dried out, with all that implies with regard to forming new compounds, would they be an equilibrium assemblage then? It seems like isotropic hydrological conditions could imply a state much like the end result of the distilled water case.<br /><br />I am thinking that if they got wet with water containing ions other than those contained in the evaporite they would not be an equilibrium assemblage.<br /><br />I am having a hard time comparing and contrasting an equilibrium assemblage with a non equilibrium one because I really don't know what it means. The abstract says 'not equilibrium assemblage and reworked by wind, water'. If that means 'not equilibrium <i> because </i> reworked by wind, water' I could understand that, but what else is there besides wind and water that makes them not an equilibrium assemblage? <div class="Discussion_UserSignature"> </div>

 

[JonClarke]

As I would understand it, an equilibrium evaporite assemblage is one whose minerals occur in the proporitions identifical to those precipitated. An equilibrium assemblage allows you to make accurate reconstructions of the parental brine.<br /><br />However, they can be redistributed by wind as you say (and this appears to have happened at Meridiani). they also also interact with later ground water of quote different composition and undergo partial dissolution and precipiattion of other salts.<br /><br />So it can get ugly. The specifics of sort of stuff soon moves out of my comfort zone. <img src="/images/icons/smile.gif" /><br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[bobw]

It must be nice to have a comfort zone. Thanks, Jon. <div class="Discussion_UserSignature"> </div>

 

[JonClarke]

It is indeed! <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[telfrow]

Hi, Jon. I saw this today and thought I'd post it in this thread. Interesting.<br /><br /><b>Geologists suggest Mars features are result of meteorite strikes, not of evaporated lakes</b><br /><br /><i>Geologic features at the Opportunity landing site on Mars were formed not by a lake that evaporated but by constant strikes from meteorites, say two Arizona State University geologists. <br /><br />The site where the Mars Exploration Rover Opportunity landed has sediments and layered structures that are thought to be formed by the evaporation of an acidic salty sea. The prevailing thought is that when this Martian sea existed it may have supported life forms and thus would be a prime site to explore for fossils. <br /><br />However, ASU geologists L. Paul Knauth and Donald Burt, who along with Kenneth Wohletz of Los Alamos National Laboratory, say that base surges resulting from massive explosions caused by meteorite strikes offer a simpler and more consistent explanation for the rock formations and sediment layers found at the Opportunity site. The researchers published their findings in the current issue of Nature. <br /><br />The research could impact where and how scientists continue their exploration of Mars in search for past life forms. <br /><br />Impact surges "present a simple alternative explanation involving deposition from a ground-hugging turbulent flow of rock fragments, salts, sulfides, brines and ice produced by a meteorite impact," the three state in their article "Impact Origin of Sediments at the Opportunity Landing Site on Mars." <br /><br />"Subsequent weathering by inter-granular water films can account for all of the features observed without invoking shallow seas, lakes or near surface aquifers," they added. "Layered sequences observed elsewhere on heavily cratered Mars and attributed to wind, water or volcanism may well have formed similarly." <br /><br />When the Opportunity lander touched down on the Meridiani Planum in January 2004, it began a very importa</i> <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>

 

[telfrow]

Also, this: <b>Mars region probably less watery than thought</b><br /><br />http://www.physorg.com/news9252.html <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>