mirrored file at http://SaturnianCosmology.Org/ For complete access to all the files of this collection see http://SaturnianCosmology.org/search.php ========================================================== Are The Mars Meteorites Really From Mars? Tom Van Flandern Meta Research ALH 84001 meteorite ALH 84001 meteorite Photo courtesy of the Johnson Space Center In August 1996, NASA scientists announced the discovery of possible microscopic bacterial life remnants in a meteorite found in Antarctica in 1984, named ALH84001. There have been previous reports of "biogenic hydrocarbons" and other life indicators in earlier meteorite studies. But this was the first evidence of primitive extraterrestrial life that had little chance to be the result of terrestrial contamination. ALH84001 belongs to a class of meteorites suspected of having an origin on the planet Mars. Originally, the primary argument for a Mars origin of this whole class of meteorites was: ÷ The 12 "Mars" meteorites show water erosion and weathering, cooling rates, oxygen isotope ratios, and other geological evidence from their pre-Earth existence that requires an origin on a major planet parent body, not of asteroidal, cometary, or Earth origin. ÷ Mars is the only known existing parent body that meets most of the necessary constraints. However, the situation is not so clear as the preceding argument might imply. The general class that the 12 Martian meteorites belong to is called "achondrites". This class name was intended to contrast these meteorites with the most common variety of stony meteorites, called "chondrites", that make up 84% of all meteorite falls found on Earth. Achondrites comprise just 8% of all such falls. Within the achondrite classification, many distinct sub-types are recognized. Three of these sub-classes represent the 12 meteorites suspected of coming from Mars: shergottites, nakhilites, and cassignites. All meteorites closely related to these three types are collectively known as SNC meteorites from the initials of the three sub-class names. These are the meteorites showing water erosion, weathering, and other evidences of origin on a major planet. The first problem with ALH84001 is that, while it is broadly similar to other SNC meteorites, it is chemically distinct enough that it does not fit easily into any of the existing sub-classes. In particular, its crystallization age is about 4.5 billion years (Gyr), similar to that of most meteorites from asteroids, but much older than all other meteorites associated with Mars (typically only 1.3 Gyr). The uniqueness of ALH84001 has led meteorite experts to propose a new sub-class called "allanites", and to add the letter "A" to the group designation, making it "SNAC" meteorites. But this proposal is not yet widely accepted. However, because ALH84001 is somewhat different from other SNC meteorites, a common Martian origin for ALH84001 is inferred purely by association, and not by direct evidence of a Martian connection in the meteorite itself. The reasoning is to assume that "if one SNC meteorite is from Mars, then they all are." Next, lets examine some of the requirements imposed on these 12 SNC meteorites if they did indeed originate on Mars. ÷ A meteorite from Mars must escape the Martian gravity field. This implies a launch speed greater than 5 km/s to exceed escape velocity. Such projectile velocities can result only from the largest of asteroidal impacts on Mars, and certainly cannot arise from even the largest volcanoes, or any other known acceleration mechanism. ÷ The meteorite-to-be must be suddenly accelerated from rest to at least 5 km/s as the impact blast wave passes, but without vaporizing. It is easy to compute the amount of energy that must be transferred to the meteorite, and the short time it has for its acceleration to escape speed. Small bodies the size of ALH84001 would normally be completely vaporized by such a shock wave transferring that much energy that quickly, and any surviving fragments of a rock barely big enough to partially survive vaporization would themselves be heavily shocked. Meteorites associated with a lunar origin, for example, apparently all had ejection velocities under 3 km/s, with survival rate decreasing sharply at the higher ejection speeds. [B.J. Gladman, J.A. Burns et al., "The exchange of impact ejecta between terrestrial planets", Science 271, 1387-1392 (1996).] ÷ ALH84001 was neither vaporized nor heavily shocked. So the rock initially ejected from Mars by the impact must have been huge compared with ALH84001, which itself must have been well-shielded deep in the interior of the larger rock. ÷ The requirements to eject relatively large rocks at speeds of at least 5 km/s with minimal shock, and the other physical and chemical constraints for SNC meteorites, place a lower limit on the size of the crater on Mars produced by the responsible Mars-impacting asteroid: at least 175 km in diameter. [A.M. Vickery and H.J. Melosh, "The large crater origin of SNC meteorites", Science 237, 738-743 (1987).] Scenarios for ejection during the formation of smaller craters are all problematical. ÷ The only craters that large on the surface of Mars are on the "old terrain", dated at least 200 million years (My) old. So the launching impact must have been at least that long ago, and the ALH84001 parent rock must have been orbiting in space for at least that long. ÷ Objects in Earth-crossing or near-Earth-crossing orbits have a half-life of just 30 My before collision with the Earth or gravitational elimination. (Common types of gravitational elimination: ejection from solar system; ejection into Jupiter-crossing orbit, collision with Jupiter; or falling into the Sun.) Almost nothing that orbits near the Earth can survive for 200 My. So the initial ejection orbit must not have come especially close to Earth. ÷ ALH84001 has been exposed to cosmic rays in space for just 15 My. This appears to contradict the previous requirement. But a consistent picture can be patched together by assuming that the parent rock of ALH84001 the one launched from Mars in the giant impact had to be at least 12 meters in diameter to shield the Mars meteorite deep in its interior from cosmic rays for most of its life. This is also consistent with the need to have a large parent body to prevent vaporization and shield ALH84001 from shock. This larger parent rock presumably had an orbit that did not venture too close to the Earth, but perhaps took it into the main asteroid belt. ÷ Then the parent rock must have been shattered 15 My ago in a collision with another sizable asteroid, exposing the ALH84001 fragment directly to cosmic rays thereafter, and altering its orbit to an Earth-crossing one. ÷ Finally, ALH84001 must have collided with the Earth and fell in Antarctica about 13,000 years ago, where it was discovered in 1984. It is noteworthy that the standard picture requires that all SNC meteorites presumably must have undergone a similar scenario, yet they must still fall to Earth during modern times more often than meteorites launched from the Moon by impacts, since "Mars" meteorites outnumber "Moon" meteorites. But with no better alternative explanations acceptable to the mainstream available, the Martian origin scenario went largely unchallenged. So it came as no surprise when one meteorite researcher produced a plot of a chemical analysis of trapped gas samples from another SNC meteorite, EETA79001, showing an almost perfect match to samples of Martian atmosphere gases taken by the Viking spacecraft. [R.O. Pepin, "Meteorites Evidence of Martian origins", Nature 317, 473-475 (1985).] Non-meteorite-experts may be forgiven for not considering what was not shown: ÷ The log-log plot hid the size of the discrepancies for individual gases. ÷ Gases were selectively plotted only for cases of relative agreement. ÷ No comparison plots to show how well the same data fit gas compositions for other source bodies, or solar system averages in general, was presented. This highly misleading paper is the original source of the assertion, quoted often in the media of late, that the case for a Mars origin was based on an "almost perfect match" with Viking samples of Martian atmospheric gases. Lets examine this match in detail. [This data is mainly from D. Bogard, "Trapped noble gases in the EETA79001 meteorite", Meteoritics 17, 185-186 (1982); R.H. Becker and R.O. Pepin, "The case for a Martian origin of the shergottites; nitrogen and noble gases in EETA79001", Earth Planet.Sci.Lett. 69, 225-242 (1984); H.Y. McSween Jr., "What we have learned about Mars from SNC meteorites", Meteoritics 29, 757-779 (1994).] Carbon dioxide (CO2) is the most abundant gas on Mars by far. Yet its relative abundance in the meteorites is but a tiny fraction of its abundance on Mars. So instead, investigators have concentrated on an isotopically heavy form of carbon that is present in similar abundances on Mars to within the broad error limits of the Viking measures. Similarly for nitrogen only the isotopically heavy form has a reasonable match between Viking and the meteorite. Yet at least one carbonaceous chondrite meteorite that nobody associates with Mars has a similar heavy nitrogen abundance. The EETA 79001 The EETA 79001. Photo courtesy of the Johnson Space Center Two key ratios in the comparison are shown in the table below. Values are listed for SNC meteorite EETA79001, Earth, and Mars. Since these ratios are very different from those in ordinary meteorites, they are the core of the case for a Martian origin. But as the Earth data shows, they do not really distinguish origin on Mars from origin on any terrestrial-type planet. - - - - - - - - - - - - 40Ar / 36Ar - - - - 129Xe / 132Xe EETA79001 - - - - -1650 - - - - - - - - -2.0 Earth - - - - - - - - - - -296 - - - - - - - - -0.98 Mars - - - - - - - - - - 3000 - - - - - - - - -2.5 This, then, is the "nearly perfect match" cited by the media. The reality is that no gases match between Mars and meteorites well enough to be persuasive of a specifically Martian origin. Excuses must be invoked for the lack of a better match for each individual gas abundance or ratio: contamination from Earth's atmosphere, seepage from the meteorite, alteration during shock or acceleration, alteration by water or weathering, etc. The case for a Martian origin is really a case based on a lack of a suitable alternative. Regular readers of the Meta Research Bulletin [MRB available from Meta Research, P.O. Box 15186, Chevy Chase, MD 20825] will not be surprised to learn of the alternative we suggest. Extensive evidence exists for the explosion of one or more bodies in or near the asteroid belt during the past half billion years of solar system history. [T. Van Flandern, "Dark Matter, Missing Planets and New Comets", North Atlantic Books, Berkeley, Ch. 11 (1993); see also "A revision of the exploded planet hypothesis", MRB 4, 33-42 (1995).] Since the explosive break-up of a larger body solves all the dynamical problems involved in delivery of the life-bearing meteorites to Earth in recent times, it should not be ignored as a viable possibility for the origin of these meteorites. As may be seen in the last reference cited, I associate the K/T boundary in the geological record on Earth with the achondritic meteorites in general, with the S-class asteroids, and with the explosion of a former terrestrial-class "Planet V" in the inner asteroid belt. In fact, this association is consistent with all the facts cited in this article regarding the origin and nature of the SNC meteorites. No low probability acceleration-to-escape-speed-from-Mars-without-vaporization event is needed. Of course, some astronomers still insist, contrary to much evidence, that planetary explosion events must themselves be of low probability. So achondritic and stony-iron meteorites in general, and SNC meteorites in particular, might be the small remaining residue of objects injected into Earth-crossing orbits perhaps 65 My ago by a planetary explosion. Planet V must have been a terrestrial-type planet with extensive water oceans and a thick atmosphere on which at least primitive life arose. And a continuing residue of fragments from that former planet still occasionally fall on Earth today at a greater rate than meteorites from recent, small lunar impacts. The cosmic ray exposure age was still probably altered by exposing fresh material in a secondary collision-in-space event; but there is no longer a need for the solar orbit of the meteorite to be significantly altered by this collision, which allows a much smaller impacting object to accomplish the secondary break-up. One remaining point deserves comment. Although the trapped gases in one SNC meteorite were no "exact match" to Mars, they were arguably closer to Mars than anything else existing today. Is that coincidence? Perhaps not, even in this alternative scenario. I did not have SNC meteorites in mind when I wrote the following last year. Rather, I was considering other evidence about Mars from the Titius-Bode law, the spin-rate of Mars, the planet's relatively small mass, and other cosmogonic considerations. I was trying to fit Mars into an evolving picture of the early solar system that included "Planet K" and "Planet V", plus the other planet-moon relationships discussed at length in "Dark Matter, Missing Planets and New Comets". I wrote, "And this [explosion of Planet V] may have been the event that delivered large quantities of water to the inner solar system, most notably to Mars (which may have still been one of Planet V's moons at the time of the explosion)." [MRB 4, 39 (1995).] That seemed a logical, but hardly compelling, possibility at the time. Since then, I have become better acquainted with the evidence for a strong hemispheric asymmetry for Mars (thanks to Jim Erjavec), with one hemisphere having most of the fresh, young craters and evidence for flowing water, and the other being apparently much older. The northern lowlands apparently sit on thin Martian crust, and the older southern uplands on thick crust. Moreover, the center of mass of the red planet is offset from its center of figure by the anomalously large amount of 3 km. [Icarus 93, 386-393 (1991).] Moreover, a strong case has been made that the crust of Mars has shifted by of order 90 degrees relative to the spin axis. [Scientific American 253, December, 94-102 (1985).] And Mars has lost the bulk of its original atmosphere. [J.Sci.Exploration 10, 355-361 (1996).] Both of these features are predictable consequences for the moon of a planet that explodes: The thickest part of the crust would tend to shift until it was nearly centered on the spin axis, and most the the original atmosphere would be blown away. All these features readily fit into a picture of Mars as a moon of Planet V when the latter exploded. One side of Mars would have been heavily impacted by the explosion, and would have accumulated much water on a temporary basis. The former planetary crust on that side would be largely destroyed, with a consequent shifting of the center of figure of the planet. Since all these unexplained anomalies actually exist on Mars, the fact that they fit so well into this scenario argues that it probably has at least an element of correctness to it. But then not only was a significant portion of Mars's atmosphere blasted away by the event, but gases and outgassing materials from Planet V would have been added to the new mix. So the present Martian atmosphere would be a mixture of its original atmosphere and gases from Planet V. This virtually guarantees that samples of Martian atmosphere today and samples of gas bubbles in meteorites from Planet V would bear a resemblance beyond chance. So I suggest for your consideration that the life-bearing meteorites originated on the former fifth planet of the solar system, Planet V, that exploded perhaps 65 million years ago, causing the demise of dinosaurs and many other species on Earth as a consequence. One day soon, Mars sample return missions will be able to test various elements of this idea directly. The hypothesis also predicts that, when we can do more comprehensive geology on the Moon, a lunar counterpart of the K/T boundary layer on Earth will be found there. In the meantime, I do not see an obvious terrestrial test that might be done unless, by serendipity, some investigator were to find trapped gas bubbles in, say, tektite glass found in the K/T layer on Earth, or some such fortuitous discovery. Tom Van Flandern's Page <../planetarysystems/vanflandern.html> The ALH 84001 Meteorite NASA Site The EETA 79001 Meteorite NASA Site ------------------------------------------------------------------------ *Planetary Mysteries * *All rights reserved. Copyright © 1996 - 2000 except where protected by previous copyright.* *This page optimized for 800 by 600 resolution with Netscape Navigator.* *For problems, please contact the WebMistress .*