Scientists find that Earth and Mars are different to the core Science and Technology Facilities Council June 28, 2007
Research comparing silicon samples from Earth, meteorites and planetary materials, published in Nature (28th June 2007), provides new evidence that the Earth's core formed under very different conditions from those that existed on Mars. It also shows that the Earth and the Moon have the same silicon isotopic composition supporting the theory that atoms from the two mixed in the early stages of their development.
This latest research which was carried out by scientists from Oxford University along with colleagues from University of California, Los Angeles (UCLA) and the Swiss Federal Institute of Technology in Zurich (ETH) compared silicon isotopes from rocks on Earth with samples from meteorites and other solar system materials. This is the first time that isotopes have been used in this way and it has opened up a new line of scientific investigation into how the Earth's core formed.
On Earth rocks that make up volcanoes and mountain ranges and underlie the ocean floor are made of silicate - compounds made of silicon and oxygen linked with other kinds of atoms. Silicate dominates down to a depth of 2,900 km - roughly half way to the centre of the Earth. At this point there is an abrupt boundary with the dense metallic iron core. Studies by Birch in the 1950's demonstrated that the outer core had a density too low to be made of pure iron and that it must also be made up of some lighter elements (see notes to editors for further details).
Research team member, Bastian Georg, a post doctoral researcher from Oxford University's Earth Sciences Department said, "We dissolved meteorites, provided by the Natural History Museum in London, in order to compare their isotopic composition with those of rocks from the Earth. The silicon was separated from other elements and the atomic proportions of isotopes measured using a particularly sophisticated mass spectrometer at the ETH in Zurich".
Professor Alex Halliday, also from Oxford University explains, "We were quite startled at our results which showed that the heavier isotopes from silicate Earth samples contained increased proportions of the heavier isotopes of silicon. This is quite different from meteorites from the silicate portions of Mars and the large Asteroid Vesta - which do not display such an effect even though these bodies also have an iron core."
Silicate samples from Mars and Vesta are identical to a primitive class of meteorites called chondrites that represent average solar system material from small "planetesimals" that never underwent core formation.
Professor Halliday continues, "The most likely explanation is that, unlike Mars and Vesta, the Earth's silicon has been divided into two sorts - a portion that became a light element in the Earth's core dissolved in metal and the greater proportion which formed the silicon-oxygen bonded silicate of the Earth's mantle and crust." At depths the silicates change structure to denser forms so the isotopic make-up would depend on the pressure at which metal and silicate separate. Quantifying this effect is the subject of ongoing studies. Co-author on the paper Edwin Schauble from UCLA, has produced preliminary calculations that show that the isotopic effects found are of the right direction and magnitude.
This research provides new evidence that the Earth's core formed under different conditions from those that existed on Mars. This could be explained in part by the difference in mass between the two planets. With Earth being eight times larger than Mars the pressure of core formation could be higher and different silicate phases may have been involved. The mass of a planet also affects the energy that is released as it accretes (or grows).
The Earth accreted most of its mass by violent collisions with other planets and planetary embryos. The bigger the planet, the greater the gravitational attraction and the higher the temperatures that are generated as the kinetic energy of impacting objects is converted to heat. Some have proposed that the outer Earth would have periodically become a "magma ocean" of molten rock as a result of such extreme high temperature events.
There is evidence that Mars stopped growing in the first few million years of the solar system and did not experience the protracted history of violent collisions that affected the Earth. There already exists compelling evidence for relatively strong magnetic fields early in martian history but a thorough understanding of the martian core must await geophysical measurements by future landers. It is however thought that the core of Mars is proportionally smaller than that of the Earth and it probably formed under lower pressures and temperatures.
The research also shows that the Moon has the same silicon isotopic composition as the Earth. This cannot be caused by high pressure core formation on the Moon which is only about one percent of the mass of the Earth. However, it is consistent with the recent proposal that the material that made the Moon during the giant impact between the proto-Earth and another planet, usually called "Theia", was sufficiently energetic that the atoms of the disk from which the Moon formed mixed with those from the silicate Earth. This means the silicon in the silicate Earth must have already had a heavy isotopic composition before the Moon formed about 40 million years after the start of the solar system.
The research was supported from grants provided by the UK's Science and Technology Facilities Council, and the USA's and Switzerland's National Science Foundation.
Contacts Gill Ormrod - Science and Technology Facilities Council Press Office Tel: 01793 442012. Email: gill.orm...@stfc.ac.uk
Pete Wilton - Oxford University Press Office Tel: 01865 283877 Email : pete.wil...@admin.ox.ac.uk
UK Science contact Professor Alex Halliday - Department of Earth Science, Oxford University Tel: 07769728153 Email: al...@earth.ox.ac.uk
Notes to Editors The information in this release in based on the following Nature paper, which appears in 28th June issue.
Silicon in the Earth's core R Bastian Georg 1,2, Alex N. Halliday 1, Edwin A Schauble 3 and Ben C Reynolds 2. 1. Department of Earth Sciences, University of Oxford 2. Department of Earth Sciences, ETH Zentrum, Zurich 3. Department of Earth and Space Science, University of California, Los Angeles.
In 1952 the distinguished Harvard geophysicist Francis Birch showed that the Earth's liquid outer core, where the magnetic field is generated, is chemically different from the solid metallic iron inner core that occupies the very centre of the Earth. Birch argued that the outer core had a density that was too low to be made of pure iron; it had to contain several percent of a lighter element or elements of lower atomic weight. Since then scientists have sought to determine what these light elements are and what their concentrations tell us about the conditions of core formation.
The Science and Technology Facilities Council ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge-exchange partnerships.
The Council has a broad science portfolio including Astronomy, Particle Physics, Particle Astrophysics, Nuclear Physics, Space Science, Synchrotron Radiation, Neutron Sources and High Power Lasers. In addition the Council manages and operates three internationally renowned laboratories: * The Rutherford Appleton Laboratory, Oxfordshire * The Daresbury Laboratory, Cheshire * The UK Astronomy Technology Centre, Edinburgh The Council gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Laboratory for Particle Physics (CERN), the Institute Laue Langevin (ILL), European Synchrotron Radiation Facility (ESRF), the European organisation for Astronomical Research in the Southern Hemisphere (ESO) and the European Space Agency (ESA). It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, and the MERLIN/VLBI National Facility, which includes the Lovell Telescope at Jodrell Bank Observatory.
> Scientists find that Earth and Mars are different to the core > Science and Technology Facilities Council > June 28, 2007
> Research comparing silicon samples from Earth, meteorites and > planetary > materials, published in Nature (28th June 2007), provides new evidence > that the Earth's core formed under very different conditions from > those > that existed on Mars. It also shows that the Earth and the Moon have > the > same silicon isotopic composition supporting the theory that atoms > from > the two mixed in the early stages of their development.
> This latest research which was carried out by scientists from Oxford > University along with colleagues from University of California, Los > Angeles (UCLA) and the Swiss Federal Institute of Technology in Zurich > (ETH) compared silicon isotopes from rocks on Earth with samples from > meteorites and other solar system materials. This is the first time > that > isotopes have been used in this way and it has opened up a new line of > scientific investigation into how the Earth's core formed.
> On Earth rocks that make up volcanoes and mountain ranges and underlie > the ocean floor are made of silicate - compounds made of silicon and > oxygen linked with other kinds of atoms. Silicate dominates down to a > depth of 2,900 km - roughly half way to the centre of the Earth. At > this > point there is an abrupt boundary with the dense metallic iron core. > Studies by Birch in the 1950's demonstrated that the outer core had a > density too low to be made of pure iron and that it must also be made > up > of some lighter elements (see notes to editors for further details).
> Research team member, Bastian Georg, a post doctoral researcher from > Oxford University's Earth Sciences Department said, "We dissolved > meteorites, provided by the Natural History Museum in London, in order > to compare their isotopic composition with those of rocks from the > Earth. The silicon was separated from other elements and the atomic > proportions of isotopes measured using a particularly sophisticated > mass > spectrometer at the ETH in Zurich".
> Professor Alex Halliday, also from Oxford University explains, "We > were > quite startled at our results which showed that the heavier isotopes > from silicate Earth samples contained increased proportions of the > heavier isotopes of silicon. This is quite different from meteorites > from the silicate portions of Mars and the large Asteroid Vesta - > which > do not display such an effect even though these bodies also have an > iron > core."
> Silicate samples from Mars and Vesta are identical to a primitive > class > of meteorites called chondrites that represent average solar system > material from small "planetesimals" that never underwent core > formation.
> Professor Halliday continues, "The most likely explanation is that, > unlike Mars and Vesta, the Earth's silicon has been divided into two > sorts - a portion that became a light element in the Earth's core > dissolved in metal and the greater proportion which formed the > silicon-oxygen bonded silicate of the Earth's mantle and crust." > At depths the silicates change structure to denser forms so the > isotopic > make-up would depend on the pressure at which metal and silicate > separate. Quantifying this effect is the subject of ongoing studies. > Co-author on the paper Edwin Schauble from UCLA, has produced > preliminary calculations that show that the isotopic effects found are > of the right direction and magnitude.
> This research provides new evidence that the Earth's core formed under > different conditions from those that existed on Mars. This could be > explained in part by the difference in mass between the two planets. > With Earth being eight times larger than Mars the pressure of core > formation could be higher and different silicate phases may have been > involved. The mass of a planet also affects the energy that is > released > as it accretes (or grows).
> The Earth accreted most of its mass by violent collisions with other > planets and planetary embryos. The bigger the planet, the greater the > gravitational attraction and the higher the temperatures that are > generated as the kinetic energy of impacting objects is converted to > heat. Some have proposed that the outer Earth would have periodically > become a "magma ocean" of molten rock as a result of such extreme high > temperature events.
> There is evidence that Mars stopped growing in the first few million > years of the solar system and did not experience the protracted > history > of violent collisions that affected the Earth. There already exists > compelling evidence for relatively strong magnetic fields early in > martian history but a thorough understanding of the martian core must > await geophysical measurements by future landers. It is however > thought > that the core of Mars is proportionally smaller than that of the Earth > and it probably formed under lower pressures and temperatures.
> The research also shows that the Moon has the same silicon isotopic > composition as the Earth. This cannot be caused by high pressure core > formation on the Moon which is only about one percent of the mass of > the > Earth. However, it is consistent with the recent proposal that the > material that made the Moon during the giant impact between the > proto-Earth and another planet, usually called "Theia", was > sufficiently > energetic that the atoms of the disk from which the Moon formed mixed > with those from the silicate Earth. This means the silicon in the > silicate Earth must have already had a heavy isotopic composition > before > the Moon formed about 40 million years after the start of the solar > system.
> The research was supported from grants provided by the UK's Science > and > Technology Facilities Council, and the USA's and Switzerland's > National > Science Foundation.
> Contacts > Gill Ormrod - Science and Technology Facilities Council Press Office > Tel: 01793 442012. Email: gill.orm...@stfc.ac.uk
> Pete Wilton - Oxford University Press Office > Tel: 01865 283877 > Email : pete.wil...@admin.ox.ac.uk
> UK Science contact > Professor Alex Halliday - Department of Earth Science, Oxford > University > Tel: 07769728153 > Email: al...@earth.ox.ac.uk
> Notes to Editors > The information in this release in based on the following Nature > paper, > which appears in 28th June issue.
> Silicon in the Earth's core > R Bastian Georg 1,2, Alex N. Halliday 1, Edwin A Schauble 3 and Ben C > Reynolds 2. > 1. Department of Earth Sciences, University of Oxford 2. Department of > Earth Sciences, ETH Zentrum, Zurich 3. Department of Earth and Space > Science, University of California, Los Angeles.
> In 1952 the distinguished Harvard geophysicist Francis Birch showed > that > the Earth's liquid outer core, where the magnetic field is generated, > is > chemically different from the solid metallic iron inner core that > occupies the very centre of the Earth. Birch argued that the outer > core > had a density that was too low to be made of pure iron; it had to > contain several percent of a lighter element or elements of lower > atomic > weight. Since then scientists have sought to determine what these > light > elements are and what their concentrations tell us about the > conditions > of core formation.
> The Science and Technology Facilities Council ensures the UK retains > its > leading place on the world stage by delivering world-class science; > accessing and hosting international facilities; developing innovative > technologies; and increasing the socio-economic impact of its research > through effective knowledge-exchange partnerships.
> The Council has a broad science portfolio including Astronomy, > Particle > Physics, Particle Astrophysics, Nuclear Physics, Space Science, > Synchrotron Radiation, Neutron Sources and High Power Lasers. In > addition the Council manages and operates three internationally > renowned > laboratories: > * The Rutherford Appleton Laboratory, Oxfordshire > * The Daresbury Laboratory, Cheshire > * The UK Astronomy Technology Centre, Edinburgh > The Council gives researchers access to world-class facilities and > funds > the UK membership of international bodies such as the European > Laboratory for Particle Physics (CERN), the Institute Laue Langevin > (ILL), European Synchrotron Radiation Facility (ESRF), the European > organisation for Astronomical Research in the Southern Hemisphere > (ESO) > and the European Space Agency (ESA). It also contributes money for the > UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, > and > the MERLIN/VLBI National Facility, which includes the Lovell Telescope > at Jodrell Bank Observatory.
- - - -
Very interesting. Perhaps mars never had a plate system like earth, but if it did, and the above is kosher, it was a bit different from our core-mantle-crustal plate movement system, I would guess. But one thing is for certain, today, mars is geologically dead. No volcanoes, no plate movement.
I had always been told that Si (silicon) did not form in nature, but if isotopes of silicon were found, perhaps it does, at extreme depths and temps?
> Scientists find that Earth and Mars are different to the core > Science and Technology Facilities Council > June 28, 2007
> Research comparing silicon samples from Earth, meteorites and > planetary > materials, published in Nature (28th June 2007), provides new evidence > that the Earth's core formed under very different conditions from > those > that existed on Mars. It also shows that the Earth and the Moon have > the > same silicon isotopic composition supporting the theory that atoms > from > the two mixed in the early stages of their development.
> This latest research which was carried out by scientists from Oxford > University along with colleagues from University of California, Los > Angeles (UCLA) and the Swiss Federal Institute of Technology in Zurich > (ETH) compared silicon isotopes from rocks on Earth with samples from > meteorites and other solar system materials. This is the first time > that > isotopes have been used in this way and it has opened up a new line of > scientific investigation into how the Earth's core formed.
> On Earth rocks that make up volcanoes and mountain ranges and underlie > the ocean floor are made of silicate - compounds made of silicon and > oxygen linked with other kinds of atoms. Silicate dominates down to a > depth of 2,900 km - roughly half way to the centre of the Earth. At > this > point there is an abrupt boundary with the dense metallic iron core. > Studies by Birch in the 1950's demonstrated that the outer core had a > density too low to be made of pure iron and that it must also be made > up > of some lighter elements (see notes to editors for further details).
> Research team member, Bastian Georg, a post doctoral researcher from > Oxford University's Earth Sciences Department said, "We dissolved > meteorites, provided by the Natural History Museum in London, in order > to compare their isotopic composition with those of rocks from the > Earth. The silicon was separated from other elements and the atomic > proportions of isotopes measured using a particularly sophisticated > mass > spectrometer at the ETH in Zurich".
> Professor Alex Halliday, also from Oxford University explains, "We > were > quite startled at our results which showed that the heavier isotopes > from silicate Earth samples contained increased proportions of the > heavier isotopes of silicon. This is quite different from meteorites > from the silicate portions of Mars and the large Asteroid Vesta - > which > do not display such an effect even though these bodies also have an > iron > core."
> Silicate samples from Mars and Vesta are identical to a primitive > class > of meteorites called chondrites that represent average solar system > material from small "planetesimals" that never underwent core > formation.
> Professor Halliday continues, "The most likely explanation is that, > unlike Mars and Vesta, the Earth's silicon has been divided into two > sorts - a portion that became a light element in the Earth's core > dissolved in metal and the greater proportion which formed the > silicon-oxygen bonded silicate of the Earth's mantle and crust." > At depths the silicates change structure to denser forms so the > isotopic > make-up would depend on the pressure at which metal and silicate > separate. Quantifying this effect is the subject of ongoing studies. > Co-author on the paper Edwin Schauble from UCLA, has produced > preliminary calculations that show that the isotopic effects found are > of the right direction and magnitude.
> This research provides new evidence that the Earth's core formed under > different conditions from those that existed on Mars. This could be > explained in part by the difference in mass between the two planets. > With Earth being eight times larger than Mars the pressure of core > formation could be higher and different silicate phases may have been > involved. The mass of a planet also affects the energy that is > released > as it accretes (or grows).
> The Earth accreted most of its mass by violent collisions with other > planets and planetary embryos. The bigger the planet, the greater the > gravitational attraction and the higher the temperatures that are > generated as the kinetic energy of impacting objects is converted to > heat. Some have proposed that the outer Earth would have periodically > become a "magma ocean" of molten rock as a result of such extreme high > temperature events.
> There is evidence that Mars stopped growing in the first few million > years of the solar system and did not experience the protracted > history > of violent collisions that affected the Earth. There already exists > compelling evidence for relatively strong magnetic fields early in > martian history but a thorough understanding of the martian core must > await geophysical measurements by future landers. It is however > thought > that the core of Mars is proportionally smaller than that of the Earth > and it probably formed under lower pressures and temperatures.
> The research also shows that the Moon has the same silicon isotopic > composition as the Earth. This cannot be caused by high pressure core > formation on the Moon which is only about one percent of the mass of > the > Earth. However, it is consistent with the recent proposal that the > material that made the Moon during the giant impact between the > proto-Earth and another planet, usually called "Theia", was > sufficiently > energetic that the atoms of the disk from which the Moon formed mixed > with those from the silicate Earth. This means the silicon in the > silicate Earth must have already had a heavy isotopic composition > before > the Moon formed about 40 million years after the start of the solar > system.
> The research was supported from grants provided by the UK's Science > and > Technology Facilities Council, and the USA's and Switzerland's > National > Science Foundation.
> Contacts > Gill Ormrod - Science and Technology Facilities Council Press Office > Tel: 01793 442012. Email: gill.orm...@stfc.ac.uk
> Pete Wilton - Oxford University Press Office > Tel: 01865 283877 > Email : pete.wil...@admin.ox.ac.uk
> UK Science contact > Professor Alex Halliday - Department of Earth Science, Oxford > University > Tel: 07769728153 > Email: al...@earth.ox.ac.uk
> Notes to Editors > The information in this release in based on the following Nature > paper, > which appears in 28th June issue.
> Silicon in the Earth's core > R Bastian Georg 1,2, Alex N. Halliday 1, Edwin A Schauble 3 and Ben C > Reynolds 2. > 1. Department of Earth Sciences, University of Oxford 2. Department of > Earth Sciences, ETH Zentrum, Zurich 3. Department of Earth and Space > Science, University of California, Los Angeles.
> In 1952 the distinguished Harvard geophysicist Francis Birch showed > that > the Earth's liquid outer core, where the magnetic field is generated, > is > chemically different from the solid metallic iron inner core that > occupies the very centre of the Earth. Birch argued that the outer > core > had a density that was too low to be made of pure iron; it had to > contain several percent of a lighter element or elements of lower > atomic > weight. Since then scientists have sought to determine what these > light > elements are and what their concentrations tell us about the > conditions > of core formation.
> The Science and Technology Facilities Council ensures the UK retains > its > leading place on the world stage by delivering world-class science; > accessing and hosting international facilities; developing innovative > technologies; and increasing the socio-economic impact of its research > through effective knowledge-exchange partnerships.
> The Council has a broad science portfolio including Astronomy, > Particle > Physics, Particle Astrophysics, Nuclear Physics, Space Science, > Synchrotron Radiation, Neutron Sources and High Power Lasers. In > addition the Council manages and operates three internationally > renowned > laboratories: > * The Rutherford Appleton Laboratory, Oxfordshire > * The Daresbury Laboratory, Cheshire > * The UK Astronomy Technology Centre, Edinburgh > The Council gives researchers access to world-class facilities and > funds > the UK membership of international bodies such as the European > Laboratory for Particle Physics (CERN), the Institute Laue Langevin > (ILL), European Synchrotron Radiation Facility (ESRF), the European > organisation for Astronomical Research in the Southern Hemisphere > (ESO) > and the European Space Agency (ESA). It also contributes money for the > UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, > and > the MERLIN/VLBI National Facility, which includes the Lovell Telescope > at Jodrell Bank Observatory.
Thanks for posting this, Ron. It answers a lot of my questions.
On a sunny day (Thu, 28 Jun 2007 09:28:36 -0700) it happened baa...@earthlink.net wrote in <1183048116.321596.151...@i38g2000prf.googlegroups.com>:
>Silicate samples from Mars and Vesta are identical to a primitive >class of meteorites called chondrites that represent average solar system >material from small "planetesimals" that never underwent core >formation.
>Professor Halliday continues, "The most likely explanation is that, >unlike Mars and Vesta,
The _most_ likely explanation is that he meteorites were not from mars in the fist place. We need real samples
> On a sunny day (Thu, 28 Jun 2007 09:28:36 -0700) it happened > baa...@earthlink.net wrote in > <1183048116.321596.151...@i38g2000prf.googlegroups.com>:
>>Silicate samples from Mars and Vesta are identical to a primitive >>class of meteorites called chondrites that represent average solar system >>material from small "planetesimals" that never underwent core >>formation.
>>Professor Halliday continues, "The most likely explanation is that, >>unlike Mars and Vesta,
> The _most_ likely explanation is that he meteorites were not from mars > in the fist place. > We need real samples
In article <c6Sgi.4622$vi5.2...@newssvr17.news.prodigy.net>, "SBC Yahoo" <atilla.the....@liberals.suck.net> wrote:
<snip>
> I had always been told that Si (silicon) did not form in nature, but if > isotopes of silicon were found, perhaps it does, at extreme depths and > temps?
From my reading of the article I got the impression that it isn't a case of different isotopes being formed, but that the primordial (supernova-produced?) mixture of isotopes gets modified in different ways in various physical/chemical environments. I suppose one might think of a phase boundary in a planet's interior as a gigantic chromatographic apparatus, tending to separate those isotopes that prefer to exist in one phase or the other.
In article <f60tvr$4j...@aioe.org>, Jan Panteltje wrote: > The _most_ likely explanation is that he meteorites were not from mars > in the fist place. > We need real samples
While agreeing with you on the need for sample return missions, the identification of certain meteorites as being form Mars is quite secure. The process of impact spalling fragments off the surface also melts small amounts of the rock on slip planes, fracture surfaces etc (unsurprisingly), and the high pressures in the impact drives bubbles of gas into this glass. Onec the rock fragment has wandered through space for a few millennia it hits the Earth's atmosphere, the surface is heated for a couple of seconds, then it crumps down into Antarctic snow or an Egyptian dog (allegedly, for the Nakhla meteorite) and is eventually found by a meteorite hunter. When the gas bubbles are identified in microscope thin sections (well, "thick sections" ; about 0.1mm, polished but no cover slip) and zapped with an ion microprobe beam, the gas composition can be measured ... and is found to have a stable isotope composition matching that measured by the Viking landers, not what we find on Earth. If you're interested, I've got the papers detailing the process somewhere. Identification of Vesta-derived meteorites is a bit less secure, based on the IR reflection spectrum of the fresh meteorite surfaces matching that of Vesta. Once the plausibility of the process had been established by the identification of the Martian meteorites, the identification of other meteorites with Vesta had much less resistance. Plus, there are a number of asteroids in related orbits to Vesta which are interpreted as debris from a recent (last few million years) large impact on Vesta. The lunar-derived meteorites are uncommon, but securely identified by correlation against Apollo samples.
-- Aidan Karley, FGS, Aberdeen, Scotland A light wave is more like a crime wave than a water wave.
In article <c6Sgi.4622$vi5.2...@newssvr17.news.prodigy.net>, SBC Yahoo wrote: > Perhaps mars never had a plate system like earth, but if > it did, and the above is kosher, it was a bit different from our > core-mantle-crustal plate movement system, I would guess.
There is (disputed) evidence for something plate-tectonic-like happening early in Mars history. A little south of the equator and covering a bit less than a quadrant of the equator, there is an area of parallel lines of differing magnetic intensity which is cross-cut and little affected by the cratering, so pre-dates the cratering. That puts it sometime between 4565 million years (construction of the planets) and approximately 3800 million years (end of the Late Heavy Bombardment, from Lunar impact metamorphism ages). And it *looks* very like the classic Reykjanes Ridge magnetic anomaly pattern.
However ... with Mars being so much smaller than the Earth, the internal temperatures are much lower, the initial heating by accretion much lower. Which changes pretty much all the details from a plate tectonic point of view.
> But one thing is > for certain, today, mars is geologically dead. No volcanoes, no plate > movement.
Almost certain. The recently announced (suspected) "skylight" openings into Martian lava tubes suggests that there's still some geological life in there ; there have been reports of transient clouds on the summits of the Tharsis volcanos which may be out-gassing ; the annual (Mars years!) movement of mass from one pole to the other is bound to have some effect ; and of course, there's the continuing aeolian deposition and re-working. This parrot hasn't quite fallen off it's perch. Yet.
-- Aidan Karley, FGS, Aberdeen, Scotland A light wave is more like a crime wave than a water wave.
In article <VA.00001410.29af9...@email.provider.invalid>, Aidan Karley <name1_na...@email.provider.invalid> wrote:
> In article <c6Sgi.4622$vi5.2...@newssvr17.news.prodigy.net>, SBC > Yahoo wrote: > > Perhaps mars never had a plate system like earth, but if it did, > > and the above is kosher, it was a bit different from our > > core-mantle-crustal plate movement system, I would guess. > There is (disputed) evidence for something plate-tectonic-like > happening > early in Mars history. A little south of the equator and covering a > bit less than a quadrant of the equator, there is an area of parallel > lines of differing magnetic intensity which is cross-cut and little > affected by the cratering, so pre-dates the cratering.
You mean there are craters in the region, but no magnetic anomalies correlate with them?
> That puts it > sometime between 4565 million years (construction of the planets) and > approximately 3800 million years (end of the Late Heavy Bombardment, > from Lunar impact metamorphism ages).
Just how did they date the periods of bombardment?
> And it *looks* very like > the classic Reykjanes Ridge magnetic anomaly pattern.
> However ... with Mars being so much smaller than the Earth, > the internal > temperatures are much lower, the initial heating by accretion much > lower. Which changes pretty much all the details from a plate > tectonic point of view.
Hm. I can understand a smaller body cooling off aster, but why would it come to a lower temperature? Except for gravitational effects, aren't its impacts as energetic as those into a larger body? Are those effects what would account for that difference?
> > But one thing is for certain, today, mars is geologically dead. No > > volcanoes, no plate movement.
> Almost certain. The recently announced (suspected) "skylight" > openings > into Martian lava tubes suggests that there's still some geological > life in there ; there have been reports of transient clouds on the > summits of the Tharsis volcanos which may be out-gassing ; the annual > (Mars years!) movement of mass from one pole to the other is bound to > have some effect ; and of course, there's the continuing aeolian > deposition and re-working. This parrot hasn't quite fallen off it's > perch. Yet.
In article <VA.0000140f.29af9...@email.provider.invalid>, Aidan Karley <name1_na...@email.provider.invalid> wrote:
>...When the gas bubbles are identified >in microscope thin sections ... and zapped with an ion microprobe >beam, the gas composition can be measured ... and is found to have a >stable isotope composition matching that measured by the Viking landers, >not what we find on Earth.
Indeed, the match to Martian air is startlingly good. The meteorites with the gas bubbles just have to have come from Mars; it would be much harder to explain them originating anywhere else.
Only some of the Martian meteorites have such gas bubbles, but they are all tied together into a family by things like odd mineralogies and unusual oxygen-isotope ratios, so establishing that a few of them are from Mars settles it fairly well for all of them. There is no longer any reasonable doubt about this.
> If you're interested, I've got the papers detailing the process >somewhere.
Try:
+ Bogard et al, "Noble gas contents of shergottites and implications for the Martian origin of SNC meteorites", Geochim.Cosmochim.Acta 48:1723-1739, 1984.
+ Becker&Pepin, "The case for a Martian origin of the shergottites: Nitrogen and noble gases in EETA 79001", Earth Planet Sci. Lett. 69:225-242, 1984.
+ Swindle et al, "Noble gases in SNC meteorites", Meteoritics 19:318-319, 1984.
+ Carr et al, "Martian atmospheric weathering products in SNC meteorites", Nature 314:248-250, 1985.
> Identification of Vesta-derived meteorites is a bit less secure... > The lunar-derived meteorites are uncommon, but securely >identified by correlation against Apollo samples.
And there are one or two peculiar meteorites which perhaps might be from Mercury, but we're unlikely to have confirmation of *that* for quite a while, since we'd need (at the very least) surface analysis by a lander, and none are planned. -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | he...@spsystems.net
On a sunny day (Tue, 17 Jul 2007 21:55:27 +0100) it happened Aidan Karley <name1_na...@email.provider.invalid> wrote in <VA.0000140f.29af9...@email.provider.invalid>:
>In article <f60tvr$4j...@aioe.org>, Jan Panteltje wrote: >> The _most_ likely explanation is that he meteorites were not from mars >> in the fist place. >> We need real samples
> While agreeing with you on the need for sample return missions, >the identification of certain meteorites as being form Mars is quite >secure. The process of impact spalling fragments off the surface also >melts small amounts of the rock on slip planes, fracture surfaces etc >(unsurprisingly), and the high pressures in the impact drives bubbles of >gas into this glass. Onec the rock fragment has wandered through space >for a few millennia it hits the Earth's atmosphere, the surface is >heated for a couple of seconds, then it crumps down into Antarctic snow >or an Egyptian dog (allegedly, for the Nakhla meteorite) and is >eventually found by a meteorite hunter. When the gas bubbles are >identified in microscope thin sections (well, "thick sections" ; about >0.1mm, polished but no cover slip) and zapped with an ion microprobe >beam, the gas composition can be measured ... and is found to have a >stable isotope composition matching that measured by the Viking landers, >not what we find on Earth. > If you're interested, I've got the papers detailing the process >somewhere. > Identification of Vesta-derived meteorites is a bit less secure, >based on the IR reflection spectrum of the fresh meteorite surfaces >matching that of Vesta. Once the plausibility of the process had been >established by the identification of the Martian meteorites, the >identification of other meteorites with Vesta had much less resistance. >Plus, there are a number of asteroids in related orbits to Vesta which >are interpreted as debris from a recent (last few million years) large >impact on Vesta. > The lunar-derived meteorites are uncommon, but securely >identified by correlation against Apollo samples.
Thank you, sounds reasonable. I made that remark inspired by yet an other posting in the trend of: 'and now we have to rethink completely about how planets and comets...' as seen often posted by NASA in sci.astro. Although I agree then methods you describe are very accurate with a low margin of error I would personally like to see some astronauts digging on mars :-) It seems our view of how planets are formed is still changing, and that would have some consequences for making statements where things come from. No mars is not geologically dead, there is a picture somewhere of a geyser like feature.. although some claim it is a dust devil... We really need to go there an look.
In article <timberwoof.spam-C671EF.15121717072...@nnrp-virt.nntp.sonic.net>,
Timberwoof wrote: > Just how did they date the periods of bombardment?
Radiometric dating and stratigraphy on lunar rocks in part, in-filled by crater counting. Some meteorites have poly-phase metamorphic and/ or igneous textures that fit broadly within the "accumulation and late heavy bombardment" model. It's not an exact science, but good enough for give-or-take of a hundred million years.
> Hm. I can understand a smaller body cooling off aster, but why would it > come to a lower temperature? Except for gravitational effects, aren't > its impacts as energetic as those into a larger body? Are those effects > what would account for that difference?
The kinetic energy of an incoming meteorite increases as the mass of the primary increases. Think of it the other way around : to raise a 1kilo meteorite off the Earth to "infinity" (or Pluto, which is an approximation to infinity) will take a certain amount of energy ; double the mass of the Earth and the same mass will need twice as much energy to be raised to infinity. Turn the rocks around now and they'll return their respective loads of kinetic energy to the planet they left. The energy delivered per kilo of the primary (Earth, Mars, whatever) doesn't change (within reason, assuming no gross changes in density, but remember that Earth is also denser than Mars due to it's own gravitational compression). But the region of space that is "hoovered clean" by the planetesimals is bigger for bigger planetesimals, so the lumps of kinetic energy arrive more frequently, the aggregating planetesimal has less time to radiate from proportionately less surface area before the next lump of kinetic energy impacts.
-- Aidan Karley, FGS, Aberdeen, Scotland A light wave is more like a crime wave than a water wave.
In article <JLCMuA....@spsystems.net>, Henry Spencer wrote: > And there are one or two peculiar meteorites which perhaps might be from > Mercury, but we're unlikely to have confirmation of *that* for quite a > while, since we'd need (at the very least) surface analysis by a lander, > and none are planned.
Be a bit harsher for them than for the Mars rovers. What is it - something like 600 K towards noon? And a diurnal range of 400 K. Severe.
-- Aidan Karley, FGS, Aberdeen, Scotland A light wave is more like a crime wave than a water wave.
In article <f7kivo$ng...@aioe.org>, Jan Panteltje wrote: > I made that remark inspired by yet an other posting in the trend of: > 'and now we have to rethink completely about how planets and comets...' > as seen often posted by NASA in sci.astro.
You'd be referring to Ron Baalke's re-posting of NASA press releases ? Well, the operative words are "press release" ; there's a fine line to tread between boring the pants off the intended audience (news editors) and over-simplifying the science beyond what the egg-heads can stomach without interrupting. I regularly have to summarise what we're seeing in a well, whether the geological objectives are being achieved, what the likely impact of today's events would be on requirements for 3 days from now ... all without confusing the audience of drillers, and often without actually telling them anything that they don't *need* to know (because the well is "tight"). I can appreciate the job that the man does - it's not easy.
> It seems our view of how planets are formed is still changing, and that > would have some consequences for making statements where things come from.
Details are being elaborated, certainly, but the broad picture hasn't significantly changed really in 20-something years. "Giant Impact" was the last really significant lump to be added to the pot ; late addition of volatiles by comets ... well, that's really been there all along (though Giant Impact has brought whole-planet fusion back to the forefront). Now, the level of detail that, for example, GRAPE computers can bring to modelling the evolution of planetary systems and the process of turning dust-clouds into planets ... that's impressive. But it's also just doing an awful lot of Newton with a couple of Cook's Constants for adhesion, inelasticity, etc.
-- Aidan Karley, FGS, Aberdeen, Scotland A light wave is more like a crime wave than a water wave.
> > In article <c6Sgi.4622$vi5.2...@newssvr17.news.prodigy.net>, SBC > > Yahoo wrote: > > > Perhaps mars never had a plate system like earth, but if it did, > > > and the above is kosher, it was a bit different from our > > > core-mantle-crustal plate movement system, I would guess. > > There is (disputed) evidence for something plate-tectonic-like > > happening > > early in Mars history. A little south of the equator and covering a > > bit less than a quadrant of the equator, there is an area of parallel > > lines of differing magnetic intensity which is cross-cut and little > > affected by the cratering, so pre-dates the cratering.
> You mean there are craters in the region, but no magnetic anomalies > correlate with them?
> > That puts it > > sometime between 4565 million years (construction of the planets) and > > approximately 3800 million years (end of the Late Heavy Bombardment, > > from Lunar impact metamorphism ages).
> Just how did they date the periods of bombardment?
Not with particularly great precision.
Basically I believe it is referenced to the moon and the few age determinations of lunar rocks. This then allows some dates to be assigned to the relative time scaled infered from crater studies.
> > And it *looks* very like > > the classic Reykjanes Ridge magnetic anomaly pattern.
> > However ... with Mars being so much smaller than the Earth, > > the internal > > temperatures are much lower, the initial heating by accretion much > > lower. Which changes pretty much all the details from a plate > > tectonic point of view.
> Hm. I can understand a smaller body cooling off aster, but why would it > come to a lower temperature? Except for gravitational effects, aren't > its impacts as energetic as those into a larger body? Are those effects > what would account for that difference?
> > > But one thing is for certain, today, mars is geologically dead. No > > > volcanoes, no plate movement.
> > Almost certain. The recently announced (suspected) "skylight" > > openings > > into Martian lava tubes suggests that there's still some geological > > life in there ; there have been reports of transient clouds on the > > summits of the Tharsis volcanos which may be out-gassing ; the annual > > (Mars years!) movement of mass from one pole to the other is bound to > > have some effect ; and of course, there's the continuing aeolian > > deposition and re-working. This parrot hasn't quite fallen off it's > > perch. Yet.
> -- > Timberwoof <me at timberwoof dot com>http://www.timberwoof.com > "When you post sewage, don't blame others for > emptying chamber pots in your direction." ‹Chris L. > an important web site:http://www.muslim-refusenik.com/
In article <VA.0000142c.0297f...@email.provider.invalid>, Aidan Karley <name1_na...@email.provider.invalid> wrote:
>> And there are one or two peculiar meteorites which perhaps might be from >> Mercury, but we're unlikely to have confirmation of *that* for quite a >> while, since we'd need (at the very least) surface analysis by a lander...
> Be a bit harsher for them than for the Mars rovers. What is it - >something like 600 K towards noon? And a diurnal range of 400 K. > Severe.
Indeed, Mercury is a harsh environment even for *orbiters*, never mind landers.
(If your orbit passes low over the sunlit side, *half the sky* is full of oven-hot planet -- a far worse thermal problem than just having rather brighter sunlight. This is why Mercury-orbiter designs tend to use quite elliptical orbits: most science instruments would benefit from more time down low, but the thermal environment is just horrible, and reasonable spacecraft designs have to spend most of their time higher up so they can cool off. An orbit over the terminator -- the day-night boundary -- would be much better, although even there you'd probably want it to be somewhat elliptical, but there's no way to *keep* an orbit over the terminator for long without advanced propulsion. A solar sail actually would work very nicely for this...)
On the surface, you can probably reduce both the peak temperature and the temperature swing by landing near one of the poles... but things still get pretty chilly at night.
ESA's BepiColombo mission originally included a small lander, but alas, that got deleted to keep the budget under control. -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | he...@spsystems.net
On Jul 17, 1:55 pm, Aidan Karley <name1_na...@email.provider.invalid> wrote:
> The lunar-derived meteorites are uncommon, but securely > identified by correlation against Apollo samples.
There's no such thing as an uncommon lunar-derived sample. They'd have to be everywhere you'd care to look. Where the hell else would that sort of displaced mega, giga if not teratonnage have gone? - Brad Guth
