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New Study Claims Mars Dry for 4 Billion Years
Today on the Web there was an item at space.com by Senior Science
Writer Robert Roy Britt, announcing the results of a study due to appear in the July 22 issue of the journal Science, in which Caltech graduate student David Shuster and Asst. Prof. Benjamin Weiss suggest that Mars hasn't had "large areas of freestanding water for four billion years", but don't rule out "pockets of isolated water in geothermal springs for periods of time". The study is based upon argon decay analysis of the remaining argon content of seven meteorites "known to have arrived from Mars after millions of years in space". The study relies on a formula for argon decay that varies with temperature. "Any way we look at it, these rocks have been very cold for a very long time," says Shuster. As of this posting, the 7/22/05 issue of Science is not yet available at its online site www.sciencemag.org . Offhand, there seem to be a number of assumptions to be justified. Whether the study does so successfully remains to be seen, though the fact that these represent elementary issues suggests that they wouldn't be overlooked. First, how is it known that the rocks weren't in space for merely "millions of years" but perhaps for billions of years? If they were thrust into space as the result of a cataclysmic event four billion years ago, and have been floating in space during the intervening time, wouldn't the study be invalidated by the fact that space is cold? Second, what were the climate patterns on Mars up until the time these rocks became spaceborn? Could they have originated in a part of Mars that was "very cold" without implicating the same climate for all the rest of the planet? Third, what were the original argon levels in these rocks, and how is this known? If volcanic, other geological, atmospheric, or even biological processes resulted in a different argon ratio than expected, could this alter the validity of the study? Other questions come to mind, but these are the primary ones that occured to me while reading the media coverage of the study. Mark Adkins |
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Dear msadkins04:
wrote in message ups.com... .... First, how is it known that the rocks weren't in space for merely "millions of years" but perhaps for billions of years? If they were thrust into space as the result of a cataclysmic event four billion years ago, and have been floating in space during the intervening time, wouldn't the study be invalidated by the fact that space is cold? The fact that these meteorites were in ice a few (to several) hundreds of thousands of years old, indicates that they were floating in space for most of the time. Space isn't cold, but the balance between a sink temperature of 3K, and the Sun at 6000K, will achieve a net temperature likely close to something between Earth and Mars... *on average*. Atmosphere only lowers that amplitude of the swings... with little or no effect on the average. David A. Smith |
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On a sunny day (21 Jul 2005 13:14:33 -0700) it happened
wrote in . com: Today on the Web there was an item at space.com by Senior Science Writer Robert Roy Britt, announcing the results of a study due to appear in the July 22 issue of the journal Science, in which Caltech graduate student David Shuster and Asst. Prof. Benjamin Weiss suggest that Mars hasn't had "large areas of freestanding water for four billion years", but don't rule out "pockets of isolated water in geothermal springs for periods of time". Like here for example: http://panteltje.com/panteltje/space...olordetail.jpg from http://panteltje.com/panteltje/space...lake2color.jpg from http://panteltje.com/panteltje/space...22_reull_v.jpg from http://sci.esa.int/science-e/www/obj...objectid=34508 all in COLOR. These springs? I do not think so, but who knows. |
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On a sunny day (21 Jul 2005 13:14:33 -0700) it happened
wrote in . com: Today on the Web there was an item at space.com by Senior Science Writer Robert Roy Britt, announcing the results of a study due to appear in the July 22 issue of the journal Science, in which Caltech graduate student David Shuster and Asst. Prof. Benjamin Weiss suggest that Mars hasn't had "large areas of freestanding water for four billion years", but don't rule out "pockets of isolated water in geothermal springs for periods of time". Like here for example: http://panteltje.com/panteltje/space...olordetail.jpg from http://panteltje.com/panteltje/space...lake2color.jpg from http://panteltje.com/panteltje/space...22_reull_v.jpg from http://sci.esa.int/science-e/www/obj...objectid=34508 all in COLOR. These springs? I do not think so, but who knows. |
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N:dlzc D:aol T:com (dlzc) wrote:
Dear msadkins04: wrote in message ups.com... ... First, how is it known that the rocks weren't in space for merely "millions of years" but perhaps for billions of years? If they were thrust into space as the result of a cataclysmic event four billion years ago, and have been floating in space during the intervening time, wouldn't the study be invalidated by the fact that space is cold? The fact that these meteorites were in ice a few (to several) hundreds of thousands of years old, indicates that they were floating in space for most of the time. Space isn't cold, but the balance between a sink temperature of 3K, and the Sun at 6000K, will achieve a net temperature likely close to something between Earth and Mars... *on average*. Atmosphere only lowers that amplitude of the swings... with little or no effect on the average. David A. Smith Dear Mr. Smith, If space isn't "cold", in the colloquial sense of this term, and with respect to the area of space occupied by these rocks during their time in space, how is it that these rocks were still *in ice*? Also, if the rocks were "known to have arrived from Mars after millions of years in space" then how is it that the ice they were encased in was only "a few (to several) hundreds of thousands of years old"? (Note that the newest ice would be closest to the surface and therefore melt away first.) Assuming, for the sake of argument, that some of the ice was burned off by atmospheric friction during meteoric entry, or even by heat from the sun while floating through space, my point remains unaltered. Finally, I fail to see how your reply is at all responsive to my question re billions vs. millions of years (how long they were in space) and what the answer implies for the validity of the study results. Mark Adkins |
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Dear msadkins04:
wrote in message oups.com... N:dlzc D:aol T:com (dlzc) wrote: Dear msadkins04: wrote in message ups.com... ... First, how is it known that the rocks weren't in space for merely "millions of years" but perhaps for billions of years? If they were thrust into space as the result of a cataclysmic event four billion years ago, and have been floating in space during the intervening time, wouldn't the study be invalidated by the fact that space is cold? The fact that these meteorites were in ice a few (to several) hundreds of thousands of years old, indicates that they were floating in space for most of the time. Space isn't cold, but the balance between a sink temperature of 3K, and the Sun at 6000K, will achieve a net temperature likely close to something between Earth and Mars... *on average*. Atmosphere only lowers that amplitude of the swings... with little or no effect on the average. If space isn't "cold", in the colloquial sense of this term, and with respect to the area of space occupied by these rocks during their time in space, how is it that these rocks were still *in ice*? Because they were "dug" out of ice that was not very old (compared to billions of years). Namely at the poles of the Earth. Also, if the rocks were "known to have arrived from Mars after millions of years in space" then how is it that the ice they were encased in was only "a few (to several) hundreds of thousands of years old"? (Note that the newest ice would be closest to the surface and therefore melt away first.) The ice record is continuous, and ages beyond the level the meteorites were discovered at. That couldn't happen through successive freeze-thaw. Assuming, for the sake of argument, that some of the ice was burned off by atmospheric friction during meteoric entry, or even by heat from the sun while floating through space, my point remains unaltered. *All* the ice was "burned off". Then it was covered with snow. Then it was packed into a glacier. Finally, I fail to see how your reply is at all responsive to my question re billions vs. millions of years (how long they were in space) and what the answer implies for the validity of the study results. It only addresses your misunderstanding about the "coldness of space". See above where you said: QUOTE wouldn't the study be invalidated by the fact that space is cold? END QUOTE Note that I said nothing to your other three (?) points, since I did not feel I could contribute rationally. Your questions there appear to be good ones to me. David A. Smith |
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Dear Mr. Smith, First, let me note that the July 22nd issue of Science is available at its Website, www.sciencemag.org and that the full text of the article in question is now available there to the general public. (Click on "see current issue" then on "research articles" then on the Mars temperature by Shuster et al.) The rocks are said to have been ejected into space some eleven million years ago, and that assertion is based upon cosmic-ray exposure testing. That opens an entirely different can of worms, so let's stick to the point of contention/confusion we've been haggling over. You say that the area of space that the rocks spent their time in (while in space) varies in temperature between 3 K and 6000 K, and that "on average" the temperature is somewhere between that of Mars and that of Earth. That's quite a variation -- anything up to 273.15 K being at or below freezing -- and it isn't clear to me how meaningful that average is, because it may merely be mathematical and of no actual bearing upon temperatures the meteorites have been exposed to. I suppose I'm confused, if that's the case, because the media description of the article said: (A) that argon decay analysis -- which is temperature sensitive -- permitted the study authors to determine that the near-surface temperature of Mars hasn't, within the last four billion years, been significantly above the current cold temperature ( 0 degrees Celsius); (B) in support of this thesis, quoted one of the study's authors as saying "However you look at it, these rocks have been very cold for a very long time". OK, you say that space, at least within the area of our Solar System where these rocks are said to have floated around for millions of years, isn't cold. Then, I don't see how these rocks could have been "very cold for a very long time". If the study's authors were merely referring to a period of a few hundred thousand years during which time they were (you've said) buried in the Earth's polar regions, how would this be relevant to the argon-decay testing thesis? The idea, I take it, is that if these rocks have remained cold, very little argon has been released, and argon levels in the rocks are comparable to what they were when on Mars. On the other hand, if they were floating around in space at temperatures above freezing for millions of years, they haven't been "very cold for a very long time". Could variations in their temperature during that period skew the argon-decay analysis in ways that would invalidate the study's conclusion? Now that I've read your reply, I'd be curious to know why these rocks fell at the Earth's poles, and what that might imply about their orbital trajectories in the period immediately before capture by the Earth. Mark Adkins |
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"m" == msadkins04 writes:
m Today on the Web there was an item at space.com by Senior Science m Writer Robert Roy Britt, announcing the results of a study due to m appear in the July 22 issue of the journal Science, in which m Caltech graduate student David Shuster and Asst. Prof. Benjamin m Weiss suggest that Mars hasn't had "large areas of freestanding m water for four billion years", but don't rule out "pockets of m isolated water in geothermal springs for periods of time". Some of your comments may be outdated, now that the actual article has appeared, but just in case that isn't so.... m The study is based upon argon decay analysis of the remaining argon m content of seven meteorites "known to have arrived from Mars after m millions of years in space". The study relies on a formula for m argon decay that varies with temperature. [...] Not decay, diffusion. (Of course, this confusion may have been generated by the space.com article.) Decay implies a nuclear reaction, which shouldn't be affected by temperature (at least not at the temperatures of interest here). Diffusion, OTOH, can be affected by temperature. The hotter a rock is, the easier it is for gasses to diffuse through it. m Offhand, there seem to be a number of assumptions to be justified. m Whether the study does so successfully remains to be seen, though m the fact that these represent elementary issues suggests that they m wouldn't be overlooked. Always be careful about assessing the validity of a scientific paper based on its press coverage. m First, how is it known that the rocks weren't in space for merely m "millions of years" but perhaps for billions of years? [...] Cosmic ray exposure. There is a host of material about this on the Web, but, simply put, the longer a rock is in space, the more cosmic rays to which it is exposed, and the more isotopes are produced in the rock from nuclear reactions. m Second, what were the climate patterns on Mars up until the time m these rocks became spaceborn? Could they have originated in a part m of Mars that was "very cold" without implicating the same climate m for all the rest of the planet? I suppose that is the case. Of course, as one would sample more and more meteorites, this case would become less and less likely. -- Lt. Lazio, HTML police | e-mail: No means no, stop rape. | http://patriot.net/%7Ejlazio/ sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html |
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Joseph Lazio wrote:
"m" == msadkins04 writes: m The study is based upon argon decay analysis of the remaining argon m content of seven meteorites "known to have arrived from Mars after m millions of years in space". The study relies on a formula for m argon decay that varies with temperature. [...] Not decay, diffusion. (Of course, this confusion may have been generated by the space.com article.) Decay implies a nuclear reaction, which shouldn't be affected by temperature (at least not at the temperatures of interest here). Diffusion, OTOH, can be affected by temperature. The hotter a rock is, the easier it is for gasses to diffuse through it. Yes, the term "decay" appeared in the space.com summarizing the (then unpublished) Science article. I thought it was a bit odd, but assumed (wrongly, as it turned out) that the senior science writer at a media outlet devoted to astronomical issues would get it right, and supposed that it was some obscure but proper nomenclature. m Offhand, there seem to be a number of assumptions to be justified. m Whether the study does so successfully remains to be seen, though m the fact that these represent elementary issues suggests that they m wouldn't be overlooked. Always be careful about assessing the validity of a scientific paper based on its press coverage. Excellent point. m First, how is it known that the rocks weren't in space for merely m "millions of years" but perhaps for billions of years? [...] Cosmic ray exposure. There is a host of material about this on the Web, but, simply put, the longer a rock is in space, the more cosmic rays to which it is exposed, and the more isotopes are produced in the rock from nuclear reactions. Might they have floated through space for billions of years without appreciable cosmic ray exposure because they were interior portions of much larger Martian rocks? By the time a meteorite reaches the surface of the Earth, it is likely to be much smaller than before it entered the atmosphere. Furthermore, it is not unthinkable that during several billion years of drifting through the solar system, in belts to which meteoritic debris is drawn, that collisions may have occurred. Now, here are two alternative scenarios, which incidentally are not mutually exclusive: (a) Eleven million years ago the rocks in question were liberated, in space collisions, from much larger rocks of which they were interior pieces, and which had previously limited their cosmic ray exposure; (b) These rocks are the remaining core pieces of a larger rock (or multiple larger rocks) whose exterior portions were burned away (and/or broke away) during entry into Earth's atmosphere and/or upon impact, and the appearance of eleven million years worth of cosmic ray exposure is really the result of a much longer exposure shielded by the layers of rock surrounding them for most of their space travel. m Second, what were the climate patterns on Mars up until the time m these rocks became spaceborn? Could they have originated in a part m of Mars that was "very cold" without implicating the same climate m for all the rest of the planet? I suppose that is the case. Of course, as one would sample more and more meteorites, this case would become less and less likely. Well, at the present time, I believe something like seven rocks were sampled. Even assuming the cosmic ray dating method is appropriate, that number is not statistically significant, particularly if they were found in the same area (on Earth), since such a grouping might be interpreted as evidence that they shared a common orbit and hence, perhaps, a common origin. -- Lt. Lazio, HTML police | e-mail: No means no, stop rape. | http://patriot.net/%7Ejlazio/ sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html Mark Adkins |
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"m" == msadkins04 writes:
m Joseph Lazio wrote: "m" == msadkins04 writes: m The study is based upon argon decay analysis of the remaining argon m content of seven meteorites "known to have arrived from Mars after m millions of years in space". [...] m First, how is it known that the rocks weren't in space for merely m "millions of years" but perhaps for billions of years? Cosmic ray exposure. There is a host of material about this on the Web, but, simply put, the longer a rock is in space, the more cosmic rays to which it is exposed, and the more isotopes are produced in the rock from nuclear reactions. m Might they have floated through space for billions of years without m appreciable cosmic ray exposure because they were interior portions m of much larger Martian rocks? By the time a meteorite reaches the m surface of the Earth, it is likely to be much smaller than before m it entered the atmosphere. Umm, why? m Furthermore, it is not unthinkable that during several billion m years of drifting through the solar system, in belts to which m meteoritic debris is drawn, that collisions may have occurred. m Now, here are two alternative scenarios, which incidentally are not m mutually exclusive: (a) Eleven million years ago the rocks in m question were liberated, in space collisions, from much larger m rocks of which they were interior pieces, and which had previously m limited their cosmic ray exposure; (b) These rocks are the m remaining core pieces of a larger rock (...) whose exterior m portions were burned away (...) during entry into Earth's m atmosphere and/or upon impact, and the appearance of eleven million m years worth of cosmic ray exposure is really the result of a much m longer exposure shielded by the layers of rock surrounding them for m most of their space travel. I guess in order to demonstrate that either of these are superior to the currently stated scenario (of an 11-million year exposure because that's how long the rock had been in space) you have to determine the following: 1) What's the cross-section for collisions? A collision would be an easy way to grind up a rock. However, the likelihood of a rock being in a collision depends upon its size. So how big does a rock have to be before it is likely to be in an appreciable collision during the lifetime of the solar system? 2) What's the size of rock have to be before cosmic-ray exposure ages are affected? Your alternate scenarios depend upon "self-shielding," the ability of outer layers of a rock to "protect" inner layers. How big does a rock have to be for that to be the case? -- Lt. Lazio, HTML police | e-mail: No means no, stop rape. | http://patriot.net/%7Ejlazio/ sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html |
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