Mars Water Debate Rages (archival thread reposting #4)

[serak_the_preparer]

AlexBlackwell<br />(<b><font color="blue">B</font>/b>)<br />11/01/02 02:14 PM<br /><br />rlb2 wrote:<br />Thanks for your reply above it was very informative.<br /><br />Alex writes:<br />You're very welcome, rlb2.<br /><br />rlb2 wrote:<br />Forgive me for repeating myself over and over from other posts but my focus on Mars is towards the Hellas basin. We have talked about this before but I am totally mystified by it.<br /><br />Alex writes:<br />No need to apolgize, rlb2. Hellas Basin is an interesting area; however, given its location it is hard to target. That said, the French have baselined Hellas for one of the four CNES NetLanders, whose launch will probably slip to 2009 at the earliest owing to the state of flux in the French Mars program. Note that the 2007 CNES PREMIER orbiter, which was once slated to perform a demonstration of future sample return technologies (e.g., aerocapture, rendezvous and capture of the sample return capsule, etc.) as well as perform orbital relay for the NetLanders and orbital science, is rumored to be on the chopping block for budgetary reasons. If so, then the NetLanders, which France and its international partners consider high priority, may have to find another ride to Mars, perhaps in conjunction with the proposed ESA 2009 ExoMars initiative. We'll have to wait and see. Oh yeah, I almost forgot to mention it. As you noted, many Mars scientists see Hellas as a very promising site to "follow the water"; however, other workers have a different take on this interpretation. See, for example, a paper published earlier this year in Geophysical Research Letters:<br /><br />====================================<br /><br />Tanaka, K. L., J. S. Kargel, D. J. MacKinnon, T. M. Hare, and N. Hoffman, Catastrophic erosion of Hellas bas</b>

 

[serak_the_preparer]

That's all for now, friends. This thread is too big to post - even in the current abridged form - all in one sitting. Besides, I'm taking my daughter out to a movie.<br /><br />Sit tight. There's more to come!<br /><br />~Serak the Preparer (Interstellar Culinary Specialist, Retired Pong Champion, Mad Archivist)

 

[serak_the_preparer]

AlexBlackwell<br />(<b><font color="blue">B</font>/b>)<br />11/01/02 02:33 PM<br /><br />cubancat wrote:<br />I'll read the papers as you say and then comment. Perhaps I'll find an image site that has a putative 'dust slide' in line with an MOLA track so we can see if the angle of repose is close to the maximum or exceeded for known materials.<br /><br />Alex writes:<br />Mind you, I'm not saying that the H2O explanation is not viable, only that I currently subscribe to the dust avalanche scar model by Sullivan et al. This is due in no small part to the details they provide along with their analysis, especially in their peer-reviewed paper in JGR-Planets, which itself is based on the preliminary results presented in the three (non peer-reviewed) LPSC abstracts that I linked.<br /><br />Like any scientist, I relish a good argument. Ferris et al. and Ahronson et al. have provided some interesting counter arguments, the former in a peer-reviewed paper in GRL, that posit an aqueous explanation for the dark streaks, or at least they argue that an aqueous explanation cannot be ruled out. Palermo et al. have a good idea, which is an extension of others' work, but the Palermo et al. paper was not very persuasive to me and, IMHO, needs a lot of work. That said, perhaps one might suggest to them that they submit their presentation, trimmed down and more focused, as an extended abstract to the upcoming 34th Lunar and Planetary Science Conference or the Sixth International Conference on Mars? As long as they stick to the "science" these venues would be good places to present their work and get feedback from the Mars co</b>

 

[serak_the_preparer]

cubancat<br />(<b><font color="yellow">F</font>/b>)<br />11/04/02 11:19 PM<br /><br />Initial observations/questions on the dust hypothesis papers you presented, Alex:<br /><br />L & PS XXX 1809, Sullivan et. al.<br />Model I) If I understand the argument correctly, then ‘seep’ lateral width should be related to slope angle. This is a <b>good model</b>, as I’ve seen the very same process as mentioned hiking in the Pike National Forest on scree slopes both below and above timberline. I could readily agree that if you disturb a scree type slope, the color change is easily visible. But, conversely, on scree slopes, I never see the digitations that one sees on ‘stain’ images. Would that be related to particle size?<br /><br />Model II) If light colored dust (i.e. CO2 snow) fell from the dark region of figure 1, then where is the evidence of the mass flow? If CO2 snow then it has possibly sublimated back into the atmosphere. If not CO2 snow then that is more problematic. This is covered in the beginning of Discussion, and indicated as a problem.<br /><br />Haven’t read about “infinite slope analysis” pg. 175-177, Slope Instability, QE598.2 .S64 1984. But the CSU library does have it, as the call number shows, if I get real ambitious.<br /><br />------------------------------------------------------------------------------------------------------------<br />Can’t agree with the proposition in L & PS XXXI 1058, Edgett et. al. Specifically the M0904689 images on page 2, Figure 1. Some of the streaks are there, but since the image is of less resolution, they appear to be of very low contrast. Examples are 3rd. streaks from bottom, left streak, M0904689, figure 1B. There’s also quite a bit of difference in the ridge about ½ up the image between Figures 1A and</b>

 

[serak_the_preparer]

voyagerwsh<br />(<b><font color="orange">K</font>/b>)<br />11/26/02 10:29 AM<br /><br />In the December issue of <i>GEOLOGY</i>, M. Gilmore et al. have a paper of Martian gullies and the implication of groundwater. Suggesting that guillies are prime cadidates to search for water and possible life.<br /><br /><i>"...gullies do not occur everywhere on Mars, suggesting to us that, as on Earth, the location of these gullies is controlled in part by the presence of an impermeable rock layer (aquiclude) that collected and concentrated local groundwater. Indeed, each of the gullies we observed emanates from a specific, cliff-forming layer, even if the layer is faulted suggesting a causal relationship. We also measured the depths of the gully heads below the local surface and found that the variation in gully depths tend to correlate to rock units interpreted to contain more impermeable layers (e.g., volcanic ash). Gully formation is therefore dependent upon both favorable climatic conditions to produce and sustain liquid water and the presence of impermeable subsurface layers to collect the groundwater. Gullies may mark the distribution of subsurface impermeable layers globally, and are prime targets for the search for present water and life on Mars."</i><br /><br />Role of aquicludes in formation of Martian gullies. GSA release 02-55: Dec. Geology & GSA Today media highlights</b>

 

[serak_the_preparer]

AlexBlackwell<br />(<b><font color="blue">B</font>/b>)<br />11/26/02 11:43 AM<br /><br />voyagerwsh wrote:<br />In the December issue of GEOLOGY, M. Gilmore et al. have a paper of Martian gullies and the implication of groundwater. Suggesting that guillies are prime cadidates to search for water and possible life.<br /><br />Alex writes:<br />Well, if one actually reads the full paper, one will note the "possible life" issue is tacked on only in the very last sentence of a four-page paper. The major thrust of the paper is <i>geological</i>, not astrobiological. Specifically, that the "location of these gullies [discovered by Malin and Edgett] is controlled in part by the presence of an impermeable rock layer (aquiclude) and that the depths of the gully heads below the surface should thus be correlated to subsurface geology." For example, the authors study a series of gullies on a segment of Martian channeled plains (unit AHh5). They discern "a single cliff-forming layer" and note that the "[g]ullies emanate from this layer even where the rock layer is faulted or disrupted...signifying a genetic relationship between the gully and the rock layer." This and other examples have led the authors to favor the aquiclude model over others (e.g., confined aquifers, geothermal heating, etc.).<br /><br />Reference:<br />Gilmore, S. and Eleyne L. Phillips, Role of aquicludes in formation of Martian gullies. Martha , Geology 30, 1107-1110, (2002).<br />Abstract<br /><br />Full access to the online article is available only to those with an online subscription.<br /><br />Alex R. Blackwell<br />University of Hawaii</b>

 

[serak_the_preparer]

cubancat<br />(<b><font color="yellow">F</font>/b>)<br />11/26/02 02:54 PM<br /><br />Saying that for them was probably like swallowing a large ice cube. It goes down, but you wonder as its being swallowed if you're going to choke.<img src="/images/icons/wink.gif" /><br /><br />I'm surprised at the anathema that science places on even the possibility of life somewhere else than on Earth. The dictum "where there's water there is life" has been found true in every ecological niche on Earth, and in some interesting places like Antarctica and embedded in rock. Why would Mars be any different? Or Europa? Or any other place in the solar system where there is unbound water or ice?<br /><br />We've advanced into the 21st. century, but some of the belief systems are decidedly medieval!<br /><br />Al<br /><br />Treason doth never prosper: what's the reason? Why, if its prosper, none dare call it treason.</b>

 

[serak_the_preparer]

AlexBlackwell<br />(<b><font color="blue">B</font>/b>)<br />11/26/02 04:12 PM<br /><br />cubancat wrote:<br />Saying that for them was probably like swallowing a large ice cube. It goes down, but you wonder as its being swallowed if you're going to choke.<br /><br />I'm surprised at the anathema that science places on even the possibility of life somewhere else than on Earth.<br /><br />Alex writes:<br />Well, your characterization is erroneous. Perhaps you need to read more journals (e.g., Astrobiology, JGR-Planets, etc.), where numerous examples of works speculating on the "possibility of life somewhere else than on Earth" have been peer-reviewed and published.<br /><br />At any rate, and as I mentioned, the Gilmore and Phillips paper was published in a geology journal, and was narrowly focused on the geology of the gully sites, not their astrobiological aspects. Therefore, there is nothing out of the ordinary with their brief mention of the gullies' exobiological potential, which has been the focus of other papers.<br /><br />Alex R. Blackwell<br />University of Hawaii</b>

 

[serak_the_preparer]

cubancat<br />(<b><font color="yellow">F</font>/b>)<br />11/26/02 04:13 PM<br /><br />Active Hydrogeomorphic Processes and the Formation of Dark Slope Streaks on Mars, Ferris, J.C. et. al., Eos Trans. AGU, 83(47),<br />Fall Meet. Suppl., Abstract xxxxx-xx, 2002<br /><br /><br /> <blockquote><font class="small">In reply to:</font><hr /><p>Mars Orbital Camera images reveal concentrations of dark slope streaks non-uniformly distributed within the equatorial region of Mars, where Late Hesperian and younger magmatic, tectonic, and fluvial activity often dominate the geologic record. Although originally ascribed to wet debris flows, all of the hypotheses published in the last ~18 years have focused on these features being solely the result of eolian or dry mass-wasting processes, excluding a role for water. In light of (1) the information provided from the Mars Global Surveyor (i.e., high-resolution imagery and topography), (2) the correlation of dark slope streak concentrations to specific geologic environments and histories portrayed in published research, and (3) geomorphic and hydrologic considerations, we hypothesize that eolian or dry mass-wasting and aqueou</p></blockquote></b>

 

[serak_the_preparer]

voyagerwsh<br />(<b><font color="red">M</font>/b>)<br />12/05/02 03:03 PM<br /><br />Contrast to commonly percieved as Mars was once warm and wet, Owen B. Toon et al. proposed model of dry and cold Mars in the <i>Journel of Science</i> that Mars was periodically bombardmented by asteroids or comets with short period of melting water from Martian ground ice as well as impactors themselves. The falling rain from the ejected stream might have curved the gullies...<br /><br />Mars May Not Have Been Warm or Wet, Study Suggests</b>

 

[serak_the_preparer]

voyagerwsh<br />(<b><font color="red">M</font>/b>)<br />12/05/02 03:24 PM<br /><br />Also, water ice discovered near south pole of Mars.<br /><br />Exposed Water Ice Discovered Near the South Pole of Mars, USGS</b>

 

[serak_the_preparer]

AlexBlackwell<br />(<b>A</b>)<br />12/05/02 04:06 PM<br /><br />voyagerwsh wrote:<br />"Contrast to commonly percieved as Mars was once warm and wet, Owen B. Toon et al. proposed model of dry and cold Mars in the Journel of Science..."<br /><br />Alex writes:<br />Minor nit. Actually the citation is Segura et al. [2002].<br /><br />Environmental Effects of Large Impacts on Mars<br />Segura, Teresa L., Owen B. Toon, Anthony Colaprete, and Kevin Zahnle<br /><i>Science</i> 298, 1977-1980, (2002).<br />Abstract<br /><br />Alex R. Blackwell<br />University of Hawaii

 

[serak_the_preparer]

AlexBlackwell<br />(<b>A</b>)<br />12/05/02 05:10 PM<br /><br />voyagerwsh wrote:<br />Also, water ice discovered near south pole of Mars.<br /><br />Alex writes:<br />This refers to a paper (see below) in Sciencexpress, a venue for early online publication of articles that will later appear in Science.<br /><br />Exposed Water Ice Discovered Near the South Pole of Mars<br />Titus, Timothy N., Hugh H. Kieffer, and Phillip R. Christensen<br />Published online December 5 2002; 10.1126/science.1080497 (Science Express Reports )<br />Abstract<br /><br /><br /><br />Alex R. Blackwell<br />University of Hawaii

 

[serak_the_preparer]

borman<br />(<b><font color="blue">B</font>/b>)<br />12/05/02 08:20 PM<br /><br />100 meter mystery<br /><br />I have wondered if there was significance to the obsevation that the gullies form 100 meters below the surface, They have been attributed to water or CO2 depending on whether one favors a wet Mars or White Mars championed by Hoffman. The Hoffman idea was once questioned because of a peculiar need for a heat source, presumeably a lava lip. This seemed a too particular requirement. But perhaps the heat could come the heat of collapse of the 100 meter layer. If the atmosphere was once much thicker in CO2 the soil could have been more saturated with it . As the atmosphere is slowly thinned by solar wind stripping and the atmospheric pressure goes quite low, gas trapped in the upper 100 meters evaporates into the atmosphere. The remaining honeycomb like structure may prove quite crush resistant but after enough weight is placed upon it, say 100 meters of rock, the honeycomb walls collapse. 100 meters of rock falling a millimeter might produce the heat for the speculated CO2 gully forming event . This would negate the need for a lava lip.<br /><br />Along these lines is the question of the apparent sedimentation exposed within craters. Its hard to point to water as there is not always an entrant or exit stream. Volcanic ash deposits have been argued to be insufficient. Hoffman has forwarded that meteor and cometary impacts could fill the gap. But then how can older craters show sedimentation? It seems to beg the question. Why can't the layers have formed over time in a quasi-metamorphic procees of successive evaporative collapses caused by exposure to a low atmosphere pressure?</b>

 

[serak_the_preparer]

AlexBlackwell<br />(<b>A</b>)<br />12/06/02 12:36 PM<br /><br />For balance, some may wish to also read a recently published paper (November 23, 2002) in the peer-reviewed Journal of Geophysical Research - Planets:<br /><br />======================================<br />Craddock, Robert A.; Howard, Alan D.<br />The case for rainfall on a warm, wet early Mars<br />10.1029/2001JE001505<br />23 November 2002<br /><br />Abstract<br /><br />Valley networks provide compelling evidence that past geologic<br />processes on Mars were different than those seen today. The generally<br />accepted paradigm is that these features formed from groundwater<br />circulation, which may have been driven by differential heating<br />induced by magmatic intrusions, impact melt, or a higher primordial<br />heat flux. Although such mechanisms may not require climatic<br />conditions any different than today's, they fail to explain the large<br />amount of recharge necessary for maintaining valley network systems,<br />the spatial patterns of erosion, or how water became initially<br />situated in the Martian regolith. In addition, there are no clear<br />surface manifestations of any geothermal systems (e.g., mineral<br />deposits or phreatic explosion craters). Finally, these models do not<br />explain the style and amount of crater degradation. To the contrary,<br />analyses of degraded crater morphometry indicate modification<br />occurred from creep induced by rain splash combined with surface<br />runoff and erosion; the former process appears to have continued late<br />into Martian history. A critical analysis of the morphology and<br />drainage density of valley networks based on Mars Global Surveyor<br />data shows that these features are, in fact, entirely consistent with<br />rainfall and surface

 

[serak_the_preparer]

AlexBlackwell<br />(<b>A</b>)<br />12/06/02 12:47 PM<br /><br />borman wrote:<br />I have wondered if there was significance to the obse[r]vation that the gullies form 100 meters below the surface...<br /><br />Alex writes:<br />Significance aside, there is a plausible geological scenario explaining this observation. As Gilmore and Phillips pointed out in their recently published paper in the journal Geology:<br /><br />"...(2) the depth of gullies below the local surface ranges from 70 to 800 m, and (3) is positively correlated to mapped geologic units. Gully formation is therefore dependent upon both favorable climatic conditions to produce and sustain liquid water and the presence of impermeable subsurface layers to collect the groundwater. Gullies may mark the distribution of subsurface impermeable layers globally...<br /><br />borman wrote:<br />The Hoffman idea was once questioned because of a peculiar need for a heat source, presumeably a lava lip. This seemed a too particular requirement.<br /><br />Alex writes:<br />That was not the only requirement of Hoffman's White Mars model, which, in fairness to Nick, has undergone a bit of tweaking since his idea was first published in the peer-reviewed journal Icarus. For example, as sources Nick postulated subsurface "liquifers" of CO2 whose existence many scientists feel is implausible over geologic time.<br /><br /><br /><br />Alex R. Blackwell<br />University of Hawaii

 

[serak_the_preparer]

voyagerwsh<br />(<b><font color="red">M</font>/b>)<br />12/06/02 01:27 PM<br /><br />Some perspectives from Michael H. Carr of USGS on the "dry model"...</b>

 

[serak_the_preparer]

AlexBlackwell<br />(<b>A</b>)<br />12/06/02 01:50 PM<br /><br />Yes, Mike Carr's comments in the SF Chronicle story were also echoed in Richard Kerr's News of the Week piece that accompanied the Segura et al. paper:<br /><br />"'Geologists say there was all this water, overflowing lakes, and massive erosion,' says planetary geologist Michael Carr of the U.S. Geological Survey in Menlo Park, California. But climate modelers can't explain why Mars would have been any warmer in its earliest days than it is today."<br /><br />[...]<br /><br />"And, more recently, geologists have recognized that great craters appear to have been filled to overflowing by rain on early Mars. 'The amount of erosion is huge,' says Carr. On the other hand, climate modelers can't stuff enough greenhouse gases into a martian atmosphere to compensate for the chilly faintness of the sun 4 billion years ago.'<br /><br />[...]<br /><br />"...Ross Irwin of the Smithsonian Institution's National Air and Space Museum in Washington, D.C., allows that impacts might have contributed to some of the earliest erosion, when the biggest asteroids were hitting, but later valley formation and the flooding of large craters seem to have required far more water than impacts could have supplied. Carr agrees that 'the valleys are only part of the problem. The amount of erosion is enormous. You're talking kilometers of water,' not the 50 meters from an impact."<br /><br /><br /><br />Alex R. Blackwell<br />University of Hawaii

 

[serak_the_preparer]

sci_man_mjl<br />(<b><font color="blue">B</font>/b>)<br />12/07/02 01:33 AM<br /><br />As i said earlier, Mars does not and probably never has had a chance for significant masses of water. The theory that it was once covered in flowing lakes and rivers is fleeting with every report that comes out such as the following:<br /><br />http://www.sciencedaily.com/releases/2002/12/021206074940.htm<br /><br />New Research Belies Previous Idea That Mars Was Once Warm, Wet Planet<br /><br />[But the study belies the warm, wet, Mars theory of rivers and oceans embraced by many planetary scientists, since such impactors were so infrequent. "There apparently were some brief warm and wet periods on Mars, but we believe that through most of its history, Mars has been a cold, dry planet," said Segura, currently a visiting researcher at NASA-Ames in California.]<br /><br />I still think that Mars only has significant ice deposits in the polar caps, and with its very erratic rotation, these come and go with tremedous frequency. The polar caps will disappear in time.</b>

 

[serak_the_preparer]

cubancat<br />(<b><font color="orange">G</font>/b>)<br />12/09/02 07:09 PM<br /><br />Sorry I can't provide a link, as this was a copy of a post off of a mailing list. Since this is the original posting on the Mars Water Debate...<br /><br /><b>DARK STREAKS ON MARTIAN SLOPES MAY SIGNAL ACTIVE WATER</b><br />From University or Arizona News Services, 520-621-1877; Writer - Agnieszka Baier<br />December 9, 2002<br /><br />Salty water driven by hot magma from Mars' deep interior may be forming some of the mysterious dark slope streaks visible near the Red Planet's equator, according to University of Arizona scientists.<br /><br />They have determined the dark slope streaks generally occur in areas of long-lived hydrothermal activity, magma-ground-ice interactions, and volcanic activity. Some of the dark slope streaks are brand new - they have formed after the Mars Global Surveyor spacecraft began detailed mapping of the planet in April 1999. Others have been observed to fade away on decadal time scales. Their findings support the hypothesis that Mars remains hydrologically active and that water could be shaping the planet's landscape today.<br /><br />Dark slope streaks were first detected using Viking Orbiter images during the early 1980s. At that time, Holly Ferguson and Baerbel Lucchitta of the U.S.G.S. in Flagstaff suggested that these features may be explained by wet debris flowing down the slopes. But all other explanations exclude a role for water and instead involve wind erosion, dust avalanching, or landslides.<br /><br />While acknowledging that dry processes can create such features, the UA researchers argue that some of the streaks' characteristics can be better explained by water seeps.<br /><br />"There is no identifiable characteristic of a dark slope</b>

 

[serak_the_preparer]

sci_man_mjl<br />(<b><font color="blue">B</font>/b>)<br />12/10/02 04:32 AM<br /><br />"The same may be happening in Tharsis or Elysium, which we believe are the long-lived zones of magma-driven activity," Dohm says. "Large intrusions of magma at depth may provide the heat to drive a regional hydrothermal system." === This is interesting, since the original assessment was that Mars had little to no magma activity.<br /><br />"This briny groundwater may be emerging through springs on the slopes of impact craters, in depressions, or along faults and fractures, Dohm adds. Since brines have a lower freezing point than pure water, they could exist at the Martian surface at current low temperatures and pressures. " === I have yet to see proof of this. We still don't know if the surface soils contain enough waters to make this feasible. Could it be that salts or other loose sediments are in these areas in significant amounts. These elements could break like ice packs under pressure from above and cause landslides. The resultant flow would look like water erosion and have a different albedo from the surrounding harder soils.<br /><br />"And where you have a long-lived heat source and ample water, there is an exciting potential for subsurface life," Dohm adds. === Good luck getting the evidence on and proving that theorem in our lifetime.<br /><br />I am still of a mind that any waters are constantly moved around the planet by its erratic orbit and the tremendous dust storms. When the polar caps are again exposed to constant sunlight due to Mars orbital eccentricity, the once equatorial region will again be saturated with ice.</b>

 

[serak_the_preparer]

borman<br />(<b><font color="blue">B</font>/b>)<br />12/14/02 11:30 PM<br /><br />Can an isothermal proccess be invoked for CO2 weathering of high lattitude Martian gullies?<br /><br />Current day weathering events on Mars have implicated water in the formation of Dark Streaks. Schorghofer, Aharonson, and Khatiwala upon analysis of some 23000 MOC images have found a correlation control at 275K implying a possible water trigger for an avalanch. Presumeably the water source is atmospheric water frost at 0.5-cm depth. Ferris et al have suggested some streaks may even be formed directly from hydrothermal briny seeps or seep path beneath. It may be possible that THEMIS’ 38 meter resolution can provide the “smoking gun” to support the Ferris immediate connection. If the hot spots are found, but do not correlate with streak location, at least a water-replenishing source is available for Schorghofer et al should normal atmospheric column density of H2O prove insufficient for frost deposition.<br /><br />Martian gully erosion occurs closer to the Martian poles than dark slope streaks constrained to a />275K line. Moreover, erosion occurs prefferentialy on slopes facing away from the sun, suggesting insolation and/or lack of it is instrumental in triggering the erosional proccess. It has been noted that during polar summers the CO2 line receeds towards the pole uncovering what is best interpreted as water ice (Boynton et al). Gully erosion is considered to be recent in the geological sense being relatively free of cratering. Water weathering has been suggested where water has been trapped at aquiludes. The outstanding problem is a heat source to keep water fluid at these more extreme lattitudes. Most arguments require some sort of geothermal heat as well as salini</b>

 

[serak_the_preparer]

voyagerwsh<br />(<b><font color="red">M</font>/b>)<br />12/16/02 11:17 AM<br /><br />Borman, tremendous floods carved Athabasca Vallis and channels in Chryse Planitia have suggested that liquid water more likely than CO2 was the erosion or impoundment agent.<br /><br />References<br /><br />1. No Mystery! Water Carved the Outflow Channels on Mars N. Coleman, Member, AGU, 252 Johnston Ln, Mercersburg, PA 17236, 2002 Fall AGU Meeting.<br /><br />2. AQUEOUS FLOWS FORMED THE OUTFLOW CHANNELS ON MARS. (PDF) Neil M. Coleman, Member, American Geophysical Union and the Health Physics Society (252 Johnston Lane, Mercersburg, PA 17236, LPSC 2002.</b>

 

[serak_the_preparer]

AlexBlackwell<br />(<b>A</b>)<br />12/16/02 04:14 PM<br /><br />A paper published online today in the Journal of Geophysical Research-Planets:<br /><br />========================================================<br />Carr, Michael H.<br />Elevations of water-worn features on Mars: Implications for circulation of groundwater<br />10.1029/2002JE001845<br />17 December 2002<br /><br />Abstract<br /><br />Central to the model of the evolution of the martian hydrosphere by<br />Clifford and Parker [2001] is a permanent freezing of the planet at<br />the end of the Noachian and recharge of the global groundwater system<br />by basal melting of ice-rich polar deposits. Acquisition of MOLA data<br />by Mars Global Surveyor provides a means of testing the model, since<br />discharge of water onto the surface, after development of the<br />cryosphere, is driven by the hydrostatic head created by the<br />difference in elevation between the base of the polar-layered terrain<br />and the discharge site. The new data show that, while most post-<br />Noachian water-worn features are at a lower elevation than the base<br />of the polar-layered terrains, as required by the model, there are<br />exceptions. Prominent among these are possible lacustrine deposits<br />within the canyons, tributaries to the canyons, and valleys on<br />several volcanoes. These high-standing features can be reconciled<br />with the model if volcanic melting of ice within the cryosphere is<br />invoked as a source for water at high elevations. An alternative is<br />that high pressures may have developed below the cryosphere as a<br />result of water being trapped beneath the growing cryosphere and the<br />impermeable basement. Yet another alternative is that, since the end<br />of the Noachian, the groundwater system has

 

[serak_the_preparer]

borman<br />(<b><font color="blue">B</font>/b>)<br />12/17/02 01:52 AM<br /><br />A further note on Dark Streaks from Schorghofer et al is a histogram of streak orientations with respect to lattitude: near the equator they are likely to be going downslope from any direction; as one goes north, sun facing slopes are preffered. This implicates insolation as integral to a putative trigger for slope streaks in general. It would not be an expectation of hydrothermal seeps which would not care about the upper centimeter as a contol. This is not to say that a seep can not occur and form a streak. In either event, a replensihing source of water would seem to be needed as these streaks are occuring in present time at present temperatures and atmosphere. Once water vapor is blown north past the 275K line it should condense and be removed from the equation upon becoming permafrost until the poles wander. The "squirtgun" model examined by Carr may prove useful in suggesting a source. Noting that the streaks are mainly grouped about the Tharsis Rise and its near antipode, the main model requirements are path and pressure and liquid water. While being near a potential heat source on the Tharsis side which may indeed contribute to additional surface sources along the same theme accounting for the greater number of streaks, the antipodal streaks may argue that volcanic heat is not a requirement. The requirement is only pressure and path in whatever form it can be attained and of course the maintenance of liquid water.<br /><br />It is getting late, and I fear this will become a rather long post which I will pick up upon later in order to explain the subject further.</b>