Re: [meteorite-list] Early Mercury Impact Showered Earth
and Jupiter tug rather strongly on this tilt, trying to straighten it out (and indeed this tilt may have been greater in the past). Without the Moon to tug on the Earth's axis and keep us reasonably precessing in a narrow range of shallow axial inclinations, the many perturbations on the Earth would push the cycle of axial precession through a wild ride on a short leash, moving Greenland and Siberia to the sub-solar point and putting Brazil in the position of Antarctica (relative to the Sun). It would be climatic chaos. Yet, Venus maintains the most circular, non-eccentric orbit in the solar system, only 0.006, and seems to continue this delicate balance of some kind of complex resonance with the Earth on a long-term basis. It's hard to imagine major life-changing immense impacts would leave no greater trace. Of course, we have to define how major major is. These early impacts (Moon-forming or Mercury crust- stripping) are low-velocity or grazing encounters with planet sized bodies, as big as Mars or bigger. The range of eccentricities and inclinations in the Asteroid Belt requires the gravitational stirring of a body at least as big as Mars passing through the Belt repeatedly. Uranus was hit hard enough to lay it right over on its side. All these events are major. They leave marks. The impact of an asteroid as big as Vesta or even Ceres on a planet like ours doesn't qualify as major from this standpoint. That impact wouldn't strip crust or form a big satellite or alter a solar orbit in the least. All it would do is boil the oceans instantly, vaporize the top few kilometers of crust, creating a 3500 degree rock vapor atmosphere, and melt the rest of the crust down to its base at the mantle. Nothing major. It interesting to note that such an incident would convert the Earth into a very convincing twin of Venus in one day flat. We would have, in a very short time, a brand-new basalt crust that was all the same age everywhere on the planet (check), a 100-bar CO2 atmosphere from the breakdown of the oceanic carbonates (check) with an equilibrium temperature of about 350 degrees C. (check), a cloud-deck with the same photochemistry as Venus (check), totally suppressed tectonics (all the plates would have been fused completely into one when the crust melted -- check), and so forth. Venus, despite all the landers, mappers, probes, and effort expended on it, remains an on-going quarrel. We thought more data would explain things; it just gets worse. Consensus about how Venus came to be what it is, what forces evolved it, and how they work today, is not in sight. It could be merely because Venus is just that different, but is annoying that no one can agree on the crustal mechanics after all that radar mapping, that we can't explain the landforms, that there are major atmospheric constituents we can't identify, that we can't unravel even the noble gas abundances, and so on. In view of all these difficulties in explaining Venus, wouldn't it be funny if it was just a case of a perfectly ordinary terrestrial planet that took just such a hit from a big asteroid as described above. That would certainly explain it very economically. Nasty way for a world to die, though. Sterling K. Webb - Original Message - From: Rob McCafferty [EMAIL PROTECTED] To: meteorite-list@meteoritecentral.com Sent: Wednesday, April 05, 2006 4:49 PM Subject: Re: [meteorite-list] Early Mercury Impact Showered Earth Definitely a thought provoking article. There are one or two things which have nagged me about Mercury and I see no reason why this article cannot point in the direction of solving them. We think that Mercury was created from a larger parent body that was involved in a catastrophic collision a large proto-planet collided with a giant asteroid about 4.5 billion years ago, in the early years of the solar system. Mercury is an unusually dense planet, which suggests that it contains far more metal than would be expected for a planet of its size, Now I know I'm not the first to suggest this, ideed, I got the idea from a professor I studied under. Could Mercury be an ex-moon of Venus? A large object hitting Venus creating it in much the same way as we predict the moon formed? I've seen a graph of (ln)Spin Angular Momentum vs (ln) mass of the planets and they all fit on the line bar the Earth, Venus and Mercury. However, Earth/moon combined does fit the line, as does Mercury/Venus combined. Is this a coincidence? That the moon is drifting out from the earth due to tidal effects and will one day be lost...The Venus/Mercury mass ratio has greater parity than Earth/moon. Could it not be that the same process took place there and Venus simply lost mercury long ago? I have never once heard this suggested in the popular press and they say some pretty far out stuff. Is this a theory which is generally considered nonsense and if so, why
Re: [meteorite-list] Early Mercury Impact Showered Earth
Hi Sterling: You left out the most recent of the impact theories: how do we get so many Trans Neptunian Objects with satellites? Large impacts! Larry __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Early Mercury Impact Showered Earth
Hi, Larry, Rob, List Well, I left it out because of its short shelf life! No sooner was it put forward, than we discovered that 2003 EL61 has two satellites in what seem to be circular, co-planar orbits, which makes impact origin pretty unlikely and then, within a week or two (before or after?), two extra satellites of Pluto with orbits in the plane of Charon. I feel sorry for whoever rushed forward with that suggestion only to be cut down in the prime of life, so to speak. A theory ought to have the shelf life of say, a Twinkie, or at the very least, a Cheeto. Just plain bad luck; it was a perfectly logical and reasonable suggestion. It's just that we don't have a universe as logical and reasonable as our theories some days. Not to get drug into another long weirdness, but one of the interesting flaws of all our theories of the origin of the solar system is that they should explain the origin of big satellite systems just as easily as they describe the origin of big planetary systems, only they don't. Whoops! In fact, the how do satellite systems form? debate is like its own little sideshow, and is a much less settled area of the theory generally. Similarly, we all believe the Titus-Bode Law is not a law at all, just a misleading coincidence, and yet, if you configure it as a power law and jigger the coefficient, presto! you have a satellite law. You can construct Titus-Bode Laws for the Jupiter, Saturn, Uranus satellite systems, all with different coefficients for each planet, but identical in form, only you have to leave out the small random satellites. As originally expressed, Titus-Bode is just a power law with a coefficient of 2.0. It fits the Solar System much better with a coefficient of 1.80 to 1.82. Satellite systems require smaller coefficients still. No explanation as to why that should be. Maybe there is something hiding under the Titus-Bode regularity that will become blindingly obvious once we figure out everything else. Sterling K. Webb --- - Original Message - From: Larry Lebofsky [EMAIL PROTECTED] To: Sterling K. Webb [EMAIL PROTECTED] Cc: Rob McCafferty [EMAIL PROTECTED]; meteorite-list@meteoritecentral.com Sent: Saturday, April 08, 2006 9:21 PM Subject: Re: [meteorite-list] Early Mercury Impact Showered Earth Hi Sterling: You left out the most recent of the impact theories: how do we get so many Trans Neptunian Objects with satellites? Large impacts! Larry __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Early Mercury Impact Showered Earth CORRECTION
Listees, The Giant Impact Theory may be improvable in the strictest sense... Doh! I meant UNPROVABLE, of course! This is what happens when you write for The List only two hours after having a large decayed canine tooth pulled, while the brain is still swimming in a pool of lidocaine... Sterling K. Webb __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Early Mercury Impact Showered Earth
Definitely a thought provoking article. There are one or two things which have nagged me about Mercury and I see no reason why this article cannot point in the direction of solving them. We think that Mercury was created from a larger parent body that was involved in a catastrophic collision a large proto-planet collided with a giant asteroid about 4.5 billion years ago, in the early years of the solar system. Mercury is an unusually dense planet, which suggests that it contains far more metal than would be expected for a planet of its size, Now I know I'm not the first to suggest this, ideed, I got the idea from a professor I studied under. Could Mercury be an ex-moon of Venus? A large object hitting Venus creating it in much the same way as we predict the moon formed? I've seen a graph of (ln)Spin Angular Momentum vs (ln) mass of the planets and they all fit on the line bar the Earth, Venus and Mercury. However, Earth/moon combined does fit the line, as does Mercury/Venus combined. Is this a coincidence? That the moon is drifting out from the earth due to tidal effects and will one day be lost...The Venus/Mercury mass ratio has greater parity than Earth/moon. Could it not be that the same process took place there and Venus simply lost mercury long ago? I have never once heard this suggested in the popular press and they say some pretty far out stuff. Is this a theory which is generally considered nonsense and if so, why? In anticipation of far more knowledgable people telling me the current state of play... R McC --- Ron Baalke [EMAIL PROTECTED] wrote: http://www.spacedaily.com/reports/Early_Mercury_Impact_Showered_Earth.html Early Mercury Impact Showered Earth SpaceDaily April 5, 2006 Leicester, England (SPX) - New computer simulations of Mercury's formation show some of the resulting ejected material ended up on Earth and Venus. The simulations, which track the material's path over several million years, also shed light on why Mercury is denser than expected. Scientists at University of Bern, Switzerland, produced the simulations, which depict the fate of material blasted out into space when a large proto-planet collided with a giant asteroid about 4.5 billion years ago, in the early years of the solar system. Mercury is an unusually dense planet, which suggests that it contains far more metal than would be expected for a planet of its size, said team leader Jonti Horner, who presented the research at a meeting of the Royal Astronomical Society. We think that Mercury was created from a larger parent body that was involved in a catastrophic collision, but until these simulations we were not sure why so little of the planet's outer layers were re-accreted following the impact. To solve the problem, the team ran two sets of large-scale computer simulations. The first examined the behavior of the material in both the proto-planet and the incoming asteroid. The simulations were among the most detailed to date, following a huge number of particles and realistically modeling the behavior of different materials inside the two bodies. At the end of the first simulations, a dense Mercury-like body remained, along with a large swathe of rapidly escaping debris. The trajectories of the ejected particles were then fed in to a second set of simulations that followed the motion of the debris for several million years. A second simulation tracked the ejected particles until they landed on a planet, were thrown into interstellar space, or fell into the Sun. The results revealed how much material would have fallen back onto Mercury and allowed the researchers to investigate ways that debris is cleared within the solar system. The group found that the fate of the debris depended on where Mercury was hit, in terms of its orbital position and the angle of the collision. Prevailing gravitational theory suggested a large fraction of the debris eventually would fall back onto the planet, but the simulations showed it would take up to 4-million years for 50 percent of the ejecta to return to Mercury, enough time for much of it to be carried away by solar radiation. This explains why Mercury retained a much smaller proportion than expected of the material in its outer layers, Horner explained. He said the simulations also showed a small fraction of the ejected material made its way to Venus and Earth - a finding that illustrates how easily material can be transferred among the inner planets. Given the amount of material that would have been ejected in such a catastrophe, Horner said, Earth could contain as much as 16 quadrillion tons of proto-Mercury particles. Related Links RAS 2006 http://www.nam2006.le.ac.uk/index.shtml Royal Astronomical Society http://www.ras.org.uk/ __ Meteorite-list mailing list
[meteorite-list] Early Mercury Impact Showered Earth
http://www.spacedaily.com/reports/Early_Mercury_Impact_Showered_Earth.html Early Mercury Impact Showered Earth SpaceDaily April 5, 2006 Leicester, England (SPX) - New computer simulations of Mercury's formation show some of the resulting ejected material ended up on Earth and Venus. The simulations, which track the material's path over several million years, also shed light on why Mercury is denser than expected. Scientists at University of Bern, Switzerland, produced the simulations, which depict the fate of material blasted out into space when a large proto-planet collided with a giant asteroid about 4.5 billion years ago, in the early years of the solar system. Mercury is an unusually dense planet, which suggests that it contains far more metal than would be expected for a planet of its size, said team leader Jonti Horner, who presented the research at a meeting of the Royal Astronomical Society. We think that Mercury was created from a larger parent body that was involved in a catastrophic collision, but until these simulations we were not sure why so little of the planet's outer layers were re-accreted following the impact. To solve the problem, the team ran two sets of large-scale computer simulations. The first examined the behavior of the material in both the proto-planet and the incoming asteroid. The simulations were among the most detailed to date, following a huge number of particles and realistically modeling the behavior of different materials inside the two bodies. At the end of the first simulations, a dense Mercury-like body remained, along with a large swathe of rapidly escaping debris. The trajectories of the ejected particles were then fed in to a second set of simulations that followed the motion of the debris for several million years. A second simulation tracked the ejected particles until they landed on a planet, were thrown into interstellar space, or fell into the Sun. The results revealed how much material would have fallen back onto Mercury and allowed the researchers to investigate ways that debris is cleared within the solar system. The group found that the fate of the debris depended on where Mercury was hit, in terms of its orbital position and the angle of the collision. Prevailing gravitational theory suggested a large fraction of the debris eventually would fall back onto the planet, but the simulations showed it would take up to 4-million years for 50 percent of the ejecta to return to Mercury, enough time for much of it to be carried away by solar radiation. This explains why Mercury retained a much smaller proportion than expected of the material in its outer layers, Horner explained. He said the simulations also showed a small fraction of the ejected material made its way to Venus and Earth - a finding that illustrates how easily material can be transferred among the inner planets. Given the amount of material that would have been ejected in such a catastrophe, Horner said, Earth could contain as much as 16 quadrillion tons of proto-Mercury particles. Related Links RAS 2006 http://www.nam2006.le.ac.uk/index.shtml Royal Astronomical Society http://www.ras.org.uk/ __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Early Mercury Impact Showered Earth
Hi, Ron Baalke posted: http://www.spacedaily.com/reports/Early_Mercury_Impact_Showered_Earth.html Early Mercury Impact Showered Earth Given the amount of material that would have been ejected in such a catastrophe, Horner said, Earth could contain as much as 16 quadrillion tons of proto-Mercury particles. That's 1.6 x10^17 tons or 1.6 x 10^20 kg. The rough estimate I posted Monday (before this article was out of embargo), made by extrapolating from Bret Gladman's 1996 simulation of meteorite transfer, was roughly 3 times greater (5 x 10^20 kg). That's about one gram per 10,000 grams of Earth. This study would put it at one gram per 31,250 grams of Earth. I'd say being within a third of an order of magnitude amounts to pretty much the same thing when you're talking either computer simulations or back-of-the-envelope scribbles! It's actually a pretty remarkable correspondence when two different methods produce such a similar result. The group found that the fate of the debris depended on where Mercury was hit, in terms of its orbital position and the angle of the collision. The two studies are quite different in their approaches. To do this new study, they had to decide on ONE impact at ONE angle and calculate from that. Hard to know which impact angle is right after 4 billion years. Gladman's original study was based on simulating 200 random impacts and so creates essentially an average impact. It's a fascinating notion, whether the Earth is 1/10,000th Mercury or 1/30,000th Mercury. One assumes that the Mercurial debris were well mixed into the early Earth, or at least its upper crust, and since have been churned by tectonics for billions of years. It would seem very unlikely that anybody could identify any component of the Earth as Mercurian in origin, particularly in such a small concentration. Making matters worse is that we don't have any way of knowing what the original Mercurian crust (which would have been blasted away to the Earth and Venus) would have been composed of, and so have no clues as to what to look for in the Earth's composition. Anyone have any rare isotopic ideas? Timing is another factor. Did the Earth get splatted with Mercurian stuff before or after our own Big Impact which formed the Moon? If it was before, then the Mercurian deposits would have been redeposited on the Moon! (There are an awful lot of refractories on the Moon, really.) Even going to Mercury wouldn't be much help, as the missing material of its former crust isn't there any more! Even the theory of the Moon's formation by a big impact has testable implications (that the Moon should be very, very dry, which it is, and highly refractory, ditto), but it's hard to think of any evidence for the Mercury Crust Removal Scenario that we didn't already have an explanation for before the theory came along. If Gladman's simulation is correct, Venus would have received 13 times more of Mercury than we did. Since Venus's crust is young (~500 million years), any Mercurian traces are gone now, even if you could go down into the Venusian Hell to look for them! We always expected Mercury to be dry and refractory because it formed near the Sun, and the big metal core used to be explained the same way. The Giant Impact Theory may be improvable in the strictest sense, at least without going to Mercury, which of course we will do eventually. Nevertheless, The Big Whack Theory is important in another sense. Belief in it implies a much more collisional history for the early Solar System than previously thought. That in turn implies a much more mixed origin for the planets than the usual view. All the differing theories of solar system origin (a la the 1990's anyway) agree on the fundamental concept of the planets having been formed from very narrow zones of fairly uniform composition. There is a body of clues accumulating that suggest it ain't necessarily so. Here are a few: a) Stardust shows us LOTS of cometary silicates. But silicates are inner solar system products. If comets were formed beyond Neptune, where'd all those silicates come from? b) Closer looks at individual asteroids show us a very wide range of compositional differences. How could they have formed in narrow zones of uniform composition? c) Many of the newly discovered Trans-Neptunian or Plutonian planets have densities that show they must be mostly or entirely rock. How could they have formed out where there was nothing but ices? Did they move around? Or are some of them captured from other stars? (Nobody likes that unlikely idea...) To make matters even worse, the discovery of a nice neat multiple satellite system around one makes a violent capture or planet-move almost impossible to conceive of. So there must have been enough inner solar system materials out beyond Pluto to form whole planets. That's enough to give a roomful of cosmogonists lifelong migraines... d) A recent dynamic study claims the
