Potential solution to meteorite mystery: Chondrules may have formed from high-pressure collisions in early solar system

Jul 08, 2013 by Steve Koppes
This is an artist's rendition of a sun-like star as it might have looked at one million years of age. As a cosmochemist, the University of Chicago's Lawrence Grossman reconstructs the sequence of minerals that condensed from the solar nebula, the primordial gas cloud that eventually formed the sun and planets. Credit: NASA/JPL-Caltech/T. Pyle, SSC

(Phys.org) —A normally staid University of Chicago scientist has stunned many of his colleagues with his radical solution to a 135-year-old mystery in cosmochemistry. "I'm a fairly sober guy. People didn't know what to think all of a sudden," said Lawrence Grossman, professor in geophysical sciences.

At issue is how numerous small, glassy spherules had become embedded within specimens of the largest class of meteorites—the chondrites. British mineralogist Henry Sorby first described these spherules, called chondrules, in 1877. Sorby suggested that they might be "droplets of fiery rain" which somehow condensed out of the cloud of gas and dust that formed the solar system 4.5 billion years ago.

Researchers have continued to regard chondrules as liquid droplets that had been floating in space before becoming quickly cooled, but how did the liquid form? "There's a lot of data that have been puzzling to people," Grossman said.

Grossman's research reconstructs the sequence of minerals that condensed from the solar nebula, the cloud that eventually formed the sun and planets. He has concluded that a condensation process cannot account for chondrules. His favorite theory involves collisions between planetesimals, bodies that gravitationally coalesced early in the history of the solar system. "That's what my colleagues found so shocking, because they had considered the idea so 'kooky,'" he said.

Cosmochemists know for sure that many types of chondrules, and probably all of them, had solid precursors. "The idea is that chondrules formed by melting these pre-existing solids," Grossman said.

One problem concerns the processes needed to obtain the high, post-condensation temperatures necessary to heat the previously condensed solid silicates into chondrule droplets. Various astonishing but unsubstantiated origin theories have emerged. Maybe collisions between in the evolving solar system heated and melted the grains into droplets. Or maybe they formed in strikes of cosmic lightning bolts, or condensed in the atmosphere of a newly forming Jupiter.

Another problem is that chondrules contain iron oxide. In the solar nebula, silicates like olivine condensed from gaseous magnesium and silicon at very high temperatures. Only when iron is oxidized can it enter the crystal structures of magnesium silicates. Oxidized iron forms at very low temperatures in the solar nebula, however, only after silicates like olivine had already condensed at temperatures 1,000 degrees higher.

At the temperature at which iron becomes oxidized in the solar nebula, though, it diffuses too slowly into the previously formed magnesium silicates, such as olivine, to give the iron concentrations seen in the olivine of chondrules. What process, then, could have produced chondrules that formed by melting pre-existing solids and contain iron oxide-bearing olivine?

"Impacts on icy planetesimals could have generated rapidly heated, relatively high-pressure, water-rich vapor plumes containing high concentrations of dust and droplets, environments favorable for formation of chondrules," Grossman said. Grossman and his UChicago co-author, research scientist Alexei Fedkin, published their findings in the July issue of Geochimica et Cosmochimica Acta.

Grossman and Fedkin worked out the mineralogical calculations, following up earlier work done in collaboration with Fred Ciesla, associate professor in , and Steven Simon, senior scientist in geophysical sciences. To verify the physics, Grossman is collaborating with Jay Melosh, University Distinguished Professor of Earth & Atmospheric Sciences at Purdue University, who will run additional computer simulations to see if he can recreate chondrule-forming conditions in the aftermath of planetesimal collisions.

"I think we can do it," Melosh said.

Chondrules are visible as round objects in this image of a polished thin section made from the Bishunpur meteorite from India. The dark grains are iron-poor olivine crystals. This is a backscattered electron image taken with a scanning electron microscope. Credit: Steven Simon

Long-standing objections

Grossman and Melosh are well-versed in the longstanding objections to an impact origin for chondrules. "I've used many of those arguments myself," Melosh said.

Grossman re-evaluated the theory after Conel Alexander at the Carnegie Institution of Washington and three of his colleagues supplied a missing piece of the puzzle. They discovered a tiny pinch of sodium—a component of ordinary table salt—in the cores of the olivine crystals embedded within the chondrules.

When olivine crystallizes from a liquid of chondrule composition at temperatures of approximately 2,000 degrees Kelvin (3,140 degrees Fahrenheit), most sodium remains in the liquid if it doesn't evaporate entirely. But despite the extreme volatility of sodium, enough of it stayed in the liquid to be recorded in the olivine, a consequence of the evaporation suppression exerted by either high pressure or high dust concentration. According to Alexander and his colleagues, no more than 10 percent of the sodium ever evaporated from the solidifying chondrules.

Grossman and his colleagues have calculated the conditions required to prevent any greater degree of evaporation. They plotted their calculation in terms of total pressure and dust enrichment in the solar nebula of gas and dust from which some components of the formed. "You can't do it in the solar nebula," Grossman explained. That's what led him to planetesimal impacts. "That's where you get high dust enrichments. That's where you can generate high pressures."

When the temperature of the solar nebula reached 1,800 degrees Kelvin (2,780 degrees Fahrenheit), it was too hot for any solid material to condense. By the time the cloud had cooled to 400 degrees Kelvin (260 degrees Fahrenheit), however, most of it had condensed into solid particles. Grossman has devoted most of his career to identifying the small percentage of substances that materialized during the first 200 degrees of cooling: oxides of calcium, aluminum and titanium, along with the silicates. His calculations predict condensation of the same minerals that are found in meteorites.

Over the last decade, Grossman and his colleagues have written a slew of papers exploring various scenarios for stabilizing iron oxide enough that it would enter the silicates as they condensed at high temperatures, none of which proved feasible as an explanation for chondrules. "We've done everything that you can do," Grossman said.

This included adding hundreds or even thousands of times the concentrations of water and dust that they had any reason to believe ever existed in the early solar system. "This is cheating," Grossman admitted. It didn't work anyway.

Instead, they added extra water and dust to the system and increased its pressure to test a new idea that shock waves might form chondrules. If shock waves of some unknown source had passed through the solar nebula, they would have rapidly compressed and heated any solids in their path, forming chondrules after the melted particles cooled off. Ciesla's simulations showed that a shock wave can produce silicate liquid droplets if he increased the pressure and the quantities of dust and water by these abnormally if not impossibly high amounts, but the droplets would be different from the chondrules actually found in meteorites today.

Cosmic shoving match

They differ in that actual chondrules contain no isotopic anomalies, whereas the simulated shock-wave chondrules do. Isotopes are atoms of the same element that have different masses from one another. The evaporation of atoms of a given element from droplets drifting through the solar nebula causes the production of isotopic anomalies, which are deviations from the normal relative proportions of the element's isotopes. It's a cosmic shoving match between dense gas and hot liquid. If the number of a given type of atoms pushed out of the hot droplets equals the number of atoms getting pushed in from the surrounding gas, no evaporation will result. This prevents isotope anomalies from forming.

The olivine found in chondrules presents a problem. If a shock wave formed the chondrules, then the olivine's isotopic composition would be concentrically zoned, like tree rings. As the droplet cools, olivine crystallizes with whatever isotopic composition existed in the liquid, starting at the center, then moving out in concentric rings. But no one has yet found isotopically zoned olivine crystals in chondrules.

Realistic-looking chondrules would result only if evaporation were suppressed enough to eliminate the isotope anomalies. That, however, would require higher pressure and dust concentrations that go beyond the range of Ciesla's shock-wave simulations.

Providing some help was the discovery a few years ago that chondrules are one or two million years younger than calcium-aluminum-rich inclusions in meteorites. These inclusions are exactly the condensates that cosmochemical calculations dictate would condense in the solar nebular cloud. That age difference provides enough time after condensation for planetesimals to form and start colliding before chondrules form, which then became part of Fedkin and Grossman's radical scenario.

They now say that planetesimals consisting of metallic nickel-iron, magnesium silicates and water ice condensed from the , well ahead of chondrule formation. Decaying radioactive elements inside the planetesimals provided enough heat to melt the ice.

The water percolated through the planetesimals, interacted with the metal and oxidized the iron. With further heating, either before or during planetesimal collisions, the magnesium silicates re-formed, incorporating iron oxide in the process. When the planetesimals then collided with each other, generating the abnormally high pressures, containing iron oxide sprayed out.

"That's where your first iron oxide comes from, not from what I've been studying my whole career," Grossman said. He and his associates have now reconstructed the recipe for producing chondrules. They come in two "flavors," depending on the pressures and dust compositions arising from the collision.

"I can retire now," he quipped.

Explore further: Student to live in simulated space habitat

More information: "Vapor saturation of sodium: Key to unlocking the origin of chondrules," by Alexei V. Fedkin and Lawrence Grossman, Geochimica et Cosmochimica Acta, Vol. 112, July 2013, pages 226-250.

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cantdrive85
1.4 / 5 (10) Jul 08, 2013
Or maybe they formed in strikes of cosmic lightning bolts


Bingo, electric discharge can explain all these anomalies without "cheating", as was suggested above.
HannesAlfven
1 / 5 (7) Jul 08, 2013
The same sort of problems -- regarding olivine, at least -- appear to plague cometary theory as well. See this ...

The Electric Comet - Full Documentary
http://www.youtub...tt2EUToo

It seems (to me at least) that the Electric Universe case on comets might be one of the strongest cases to be made for a far more recent planetary catastrophe. In the EU view, comets and asteroids would have similar origins, but different orbits -- comets being those items which which were ejected at far higher velocity from the claimed interaction, which then causes them to pick up more electrons further away from the Sun, which causes a brighter electrical discharge as they then move back through the Sun's (claimed) electric field.

I don't envy the theorists who are trying to fit all of these enigmas to conventional theory. This is essentially a history of the universe here which is being proposed. The levels of uncertainty involved are necessarily off-the-charts.
Torbjorn_Larsson_OM
5 / 5 (5) Jul 08, 2013
The problem for the "EU" crackpots is that the work showed that "EU" didn't work (and it never has). "Various astonishing but unsubstantiated origin theories have emerged. ... Or maybe they formed in strikes of cosmic lightning bolts, or ..." If "EU" predicted "cosmic lightning bolts", which is doubtful since there is nothing published in peer review, it wasn't useful.

Those deficiencies lead to a non-astonishing, substantiated predictive theory that _is_ useful. Problem solved, alleged "uncertainties" removed. (And crackpottery like "EU" rejected once again.)

Shootist
1 / 5 (3) Jul 08, 2013
The problem for the "EU" crackpots is that the work showed that "EU" didn't work (and it never has). "Various astonishing but unsubstantiated origin theories have emerged. ... Or maybe they formed in strikes of cosmic lightning bolts, or ..." If "EU" predicted "cosmic lightning bolts", which is doubtful since there is nothing published in peer review, it wasn't useful.

Those deficiencies lead to a non-astonishing, substantiated predictive theory that _is_ useful. Problem solved, alleged "uncertainties" removed. (And crackpottery like "EU" rejected once again.)



The UK's replacement for David Attenborough, Brian Cox, was recently heard touting electrostatics as the probably source of chondrules made from dust bits (held together by van Der Waall force) suddenly heated to 3000C by the resultant static discharge (lighting in the primordial dust cloud).
cantdrive85
1 / 5 (7) Jul 08, 2013
Or maybe they formed in strikes of cosmic lightning bolts, or ..." If "EU" predicted "cosmic lightning bolts", which is doubtful since there is nothing published in peer review, it wasn't useful.

Haha, and who exactly would peer review it? Oh right, experts in electrical discharge and plasma cicuitry, like the folks at the IEEE. Strangely, that's where most PC and EU papers are published. If you're not aware of the predicted "cosmic lightning bolts" then you are COMPLETELY ignorant of EU and its most basic tenets. How valuable is an opinion based on utter ignorance? As valuable as larssens. BTW, one of their books is called 'Thunderbolts of the Gods', and it's not about theology. Rube
HannesAlfven
1 / 5 (4) Jul 09, 2013
Re: "which is doubtful since there is nothing published in peer review"

That's funny, because I have so many "peer-reviewed" papers on my hard drive which pertain to this subject that it's clear that I could spend an entire lifetime reading it. Have you considered that you simply don't know what the theory says, in order to know where to look? I mean, IEEE's Transactions on Plasma Science never stopped publishing on plasma cosmology since the days of Hannes Alfven.

It's really quite amusing that some people have fully bought into the notion that there is only one paradigm which can explain our observations in cosmology and astrophysics. It's very revealing that most press releases fail to even mention for people learning the "mainstream" views all of the assumptions and delicate structure involved with each claim. This press release fairs better than most, but the track record on this point is startling. Students are not even taught that Alfven disagreed with MHD's application!
HannesAlfven
1 / 5 (4) Jul 09, 2013
"Professionals generally avoid the risk inherent in real critical thinking and cannot properly be called critical thinkers. They are simply ideologically disciplined thinkers. Real critical thinking means uncovering and questioning social, political and moral assumptions; applying and refining a personally developed worldview; and calling for action that advances a personally created agenda. An approach that backs away from any of these three components lacks the critical spirit ... Ideologically disciplined thinkers, especially the more gung-ho ones, often give the appearance of being critical thinkers as they go around deftly applying the official ideology and confidently reporting their judgments. The fact that professionals are usually more well-informed than nonprofessionals contributes to the illusion that they are critical thinkers."

Disciplined Minds, Jeff Schmidt (fired by the AIP for writing this book, largest freedom-of-expression case in history of physics discipline)
HannesAlfven
1 / 5 (4) Jul 09, 2013
"Because they internalize both the paradigms and their employers' priorities and values, scientists, at least in their own eyes, are completely nonpartisan in their work: They don't 'get political.' They don't think about, let alone challenge, the ideology built into their techniques. Contrary to popular images of scientists as challengers of established beliefs (like Galileo or Einstein), the vast majority of scientists never seek to test their paradigms and do not participate in paradigm disputes. They don't waste their employers' coin by getting caught up in efforts to overthrow existing worldviews or to establish new ones. Instead, they tend to treat the accepted models of reality as reality itself."

Disciplined Minds, Jeff Schmidt (he won his court case against the AIP, with the support of Noam Chomsky and the signatures of more than 1,000 other researchers; and yet, to this day, people pretend like it never happened, as if the book was never written ...)
HannesAlfven
1 / 5 (4) Jul 09, 2013
"Professionals look beneath the surface of their technical work and see a world of contending social forces. Where the nonprofessional might see only technical details, the professional sees sides of debates being supported, points of view being advanced and interests being served."

"Professionals, on the other hand, are required to be creative in their work -- but within strict political limits. Their creativity must serve their employers' interests, which often are not the same as their own interests, the interests of clients or customers or the public interest ... The professional's lack of control over the political content of his or her creative work is the hidden root of much career dissatisfaction."

Is this the system you thought you were defending? Seems to me that the reality of the physics discipline long ago departed the ideal which the public continues to hold in its mind about what it means to "think like a scientist".
cantdrive85
1 / 5 (4) Jul 09, 2013
yet, to this day, people pretend like it never happened, as if the book was never written ...


There is a tremendous amount of ignorance in the small specialized insular group we call astrophysicists. To our dismay their main thrust of research, plasma, is also that which they are completely ignorant. One day science/society will reflect on the current paradigm of "science" with as much contempt as we do epicycles. It's shameful to be associated with the era of the "dark sciences".
HannesAlfven
1 / 5 (4) Jul 09, 2013
"A faculty member who talks informally with a student in the hallway or at the weekly after-colloquium reception inevitably comes away with a feeling about whether or not that student 'thinks like a physicist.' The student's political outlook can easily make a difference in the faculty member's assessment. For example, in the usual informal discussion of an issue in the news, the student who rails against technical incompetence and confines his thoughts to the search for technical solutions within the given political framework builds a much more credible image as a professional physicist than does the student who emphasizes the need to alter the political framework as part of the solution. Indeed, the latter approach falls outside the work assignments given to professional physicists in industry and academe and so represents thinking unlike a physicist's."

Do you think that this is an effective approach to a unification theory in physics? Does nature care about the games we play?
HannesAlfven
1 / 5 (4) Jul 09, 2013
Re: "To our dismay their main thrust of research, plasma, is also that which they are completely ignorant."

I've rummaged through quite a few of their textbooks. They do indeed mention plasmas quite frequently. The pattern which I see is that they tend to teach plasmas strictly in terms of mathematical formalism. This seems problematic to me because the cosmic plasma models have been the subject of critique for many decades now. I believe that the most serious problem is that the students are not told of any controversy whatsoever -- even though Alfven himself repeatedly recused himself from the way in which the models were being applied. And without a strong conceptual understanding for how plasmas are observed to behave in the laboratory, it's nearly impossible for the students to question these cosmic plasmas models. It's (btw) been shown by Eric Mazur at Harvard that problem-solving skills improve when students are taught the concepts first.