Extraterrestrial Organic Chemistry in Meteorites
Unraveling the Organic Chemistry of the Early Solar System by Solid State NMR Spectroscopy, X-ray Absorption Near Edge Spectroscopy (XANES), and Pyrolysis Gas Chromatography-Mass Spectrometry (Pyr-GCMS)- The amazing story ET organic solids tell!
Figure 1 (Right): This amazing image of the trail of the Tagish Lake meteorite I found on a Candian web site documenting the fall and collection of the Tagish Lake meteorite in Western Canada, British Columbia. I know it looks like the meteoroid is rising into the sky, but this is an illusion. Actually this image could be fake! I really don't know- I do know that the Tagish Lake meteorite did land and has turned out to be an amazing fall.
What this image serves to document the fact that the solar system “kindly” provides samples of its earliest history to us via meteorite impact- all the time!. It also reminds us that the Tagish Lake meteorite might be the most important chondritic meteorite from an "organic POV" that enables us invaluable insight into what goes on inside a planetesimal interior (THANK YOU CANADA!- and Chris Herd, CA's Lead Scientist on this amazing acquisition). I am beginning to believe that the Tagish Lake meteorite might truly be the "Rosetta Stone" for understanding meteoritic organic solids.
BACKGROUND: Primitive meteorites (e.g. carbonaceous chondrites) are the remnants of the earliest accreted objects in our Solar System. Meteorites are fragments of asteroids that are fragments of early planetesimals (small worlds) that formed and existed (perhaps for tens or hundreds of millions of years) until they were destroyed by massive collisions with other planetesimals. The size of these planetesimals were too small to under go planetary melting and core mantle differentiation (like Mars, Earth, Venus and Mercury). In principal carbonaceous chondrites (and other chondrites) provide the un-mixed ingredients from a which an "Earth" might be made.
I have focused my research on a sub-constituent of such primitive meteorites - complex organic solids (these are insoluble in any solvent so we call them Insoluble Organic Matter, IOM). IOM is the primitive carrier of much of Solar System carbon (carbonate is the other) and likely all of the Solar system nitrogen (that could make it into a accreted planet).
The fact that carbonaceous chondrites contain (relatively) a lot of organic carbon ( ~ 2 wt %) is really cool and has intrigued scientists for over 50 years. In the 1980's it was shown that this IOM was relatively enriched in deuterium. Now, deuterium is the rarest of the stable isotopes, formed exclusively during the big bang and is very rare. The thinking is that the means by which D could be enriched is through very low temperature isotope fractionation. Thus, high D content is generally considered to ultimately be a signature of very cold chemistry. I agree- the precursor of IOM had to have formed in the interstellar medium.
From the perspective of IOM's origins, many have concluded that as it typically has a high D/H, then these organic solids must have also formed under very cold conditions. The most frequently proposed scenario has been UV-photolysis of interstellar ice mantles on silicate grains from which planetesimals are thought to accrete. I have a problem with this hypothesis- FIRST: specifically interstellar ices (and cometary ices) are predominantly composed of water ice. UV photolysis of water ice produces predominantly OH• radicals- such radicals will destroy any organics- not form them (this is established in the literature with water rich ices). SECOND: organic solids in chondrites exhibit complex morphologies including abundant hollow spheres (SEE FIGURE). These morphologies "scream" of liquid medium processing. It simply does not seem reasonable to presume that such objects formed at interstellar temperatures (~ 20 K or even 120 K); rather IOM morphology suggests to me polymerization must have occurred in a liquid medium- only possible in a planetesimal interior- in liquid water.
I and a number of former post Docs (now PI's on their own!) in my laboratory have been exploring a different scenario: SCENARIO: IOM formed from the reaction of simple interstellar molecules (e.g. formaldehyde) after planetesimal accretion in the warm and wet interiors of planetesimals. This is an idea we can test in the laboratory and we do just that (e.g. Cody et al. PNAS 2011, Kebukawa et al. ApJ. 2013, Kebukawa and Cody Icarus 2015). We find our laboratory generated organic solid products are chemically (nearly) identical to IOM and morphologically the same (lots of hollow balls- aka "nanoglobules").
We are now working on establishing what D/H ratio's in IOM actually mean and more recently are seeking explanations for 13C abundances and 15N abundances in IOM. We have previously found a way to use IOM electronic structure as a cosmochemical thermometer (Cody et al. EPSL 2008); we have made a solid connection between cometary organic solids (outer solar system) with chondritic IOM (inner solar system) (Cody et al. PNAS 2011); we have shown that IOM molecular structure is evolved through hydrothermal processing in plantesimal interiors (Cody and Alexander 2005; Herd et al Science 2011; Alexander et al. MAPS 2015); we are in the works to better understand how IOM passes through terrestrial planet formation to provide terrestrial C and N abundances: we have found a way of measuring D-NMR spectra of IOM - something I thought initially was impossible (Thanks to Ying Wang for pushing us here!)- it is possible (in works to be published- although there is a Wang et al. LPSC abstract 2011). Basically we are pretty busy on using IOM molecular structure to help understand early Solar System History.
Please stay tuned! We are making progress here.
My work with extraterrestrial solids has been part of a long term collaboration with the following wonderful individuals (in quasi chronological and no particular order- all are amazing!):
- Conel Alexander- Staff Member Carnegie DTM- Conel got me started on this even before I joined Carnegie and Conel and I are still working/arguing and publishing on this topic.
- Hikaru Yabuta, Hiroshima University- Hikaru and I worked on the StarDust Samples and the Exciton thermometer as well on a number of very cool papers on moderately altered meteorites- Hikaru is now a team leader for the Hayabusa 2 mission.
- Yoko Kebukawa, Yokohama National University- Yoko and I continue to work on IOM synthesis from formaldehyde- Yoko is leading her own innovative and exciting initiatives into studies of Extraterrestrial materials and is teaming up to participate in future JAXA space missions.
- Ying Wang, Georgia Tech- Ying inspired me to find a way to do natural abundance D Solid state NMR which has provided unique understanding of what D/H means in extraterrestrial IOM and beyond this enabled us to identify wild and unexpected intramolecular D/H fractionation within sites in hydrous silicate glasses.
- A. David Kilcoyne, ALS, LBL, Harald Ade NCSU, Adam Hitchcock. McMaster- David enabled all of us to get the best data you could hope for from the STXM- Harald Ade saw at the beginning the importance of high quality XANES at nanoscales- Harald Ade was also a visionary for STXM as an analytical tool- hence the "polymer stxm" at ALS. Adam Hitchcock enlightened me and the world about the analytic qualities of C-, N-, and O-XANES: if a Nobel prize were given for STXM/light element XANES it would be tough to find just three. Of course, Janos Kirz and Chris Jacobsen were critical- no Soft X-ray optics- No STXM!, but I think that for chemical spectroscopy- I would say that Harald and Adam pushed the spectroscopy and David Kilcoyne was the master at making the best instrument ever conceived. Really all a bunch of geniuses here! Thank you all!
- Sue Wirick- X1A STXM- the first and my total first collaborator with STXM. Thank you Sue!
- Marilyn Fogel (GL now UCR) and Roxanne Bowdin: All of the bulk H/C, N/C, and O/C plus all bulk isotopes on chondritic IOM were done by Marilyn and Roxanne.
- Larry Nittler, Staff Member Carnegie DTM- Larry and I collaborated on a wide range of organic cosmochemistry questions.
- Rhonda Stroud and Brad Degregorio, NRL- Rhonda and Brad have brought TEM to the IOM problem in particular revealing the spectacular nano-morphology exhibited by IOM.
- Chris Herd (U Alberta, CA)- Chris created the Tagish Lake consortium- this meteorite might well be the "Rosetta Stone" of meteorites.
- Summer Research Interns, Jean Lee, Emily Heying, Giovani Amodeo, and others.
FIGURE 2: Scanning Transmission Soft X-ray Microscope (STXM) Image of a FIB section of the ordinary chondrite QUE97008, that is very similar to the famous chondrite Semarkona (a pair?). What we see at the submicron level (View is 3 x 5 microns) is revealed by element filtered imaging 1) on the Carbon K-edge (RED), 2) Calcium L-edge (GREEN) and 3) the Iron L-edge (BLUE). For scale: The hollow RED (carbon-rich) ball ( a "nanoglobule") is ~ 500 nm in diameter.
Blue grains are largley olivine, Green are CPX and RED are pure Extraterrestrial organic solids, we call these Insoluble Organic Matter (IOM). We study IOM to understand the formation and evolution of the early Solar System. How do you think tiny hollow balls of solid organic carbon formed? I have my thoughts!
Note: the hollow ball is actually hollow- this nearly perfectly spherical ball formed somewhere in the early solar system and its shape is governed by the physicochemical nature of its synthesis- BTW, yes there does appear to be a Ca-rich rim inside it- how about that!.... In my view such objects could only be formed in an aqueous medium.
Open to other ideas.... Do you have any? Please let me know.
Note this image was made using AXIS2000 software.
Figure 3 (Right): This is an image of piece of the Tagish Lake meteorite, recovered from the ice in British Columbia, that was kindly passed to meteorite scientist, Mike Zolensky (NASA, JSC) [this image was obtained courtesy of Google “Tagish Lake” from Mike Zolensky, NASA, JSX]. Please note that the block on the left is a centimeter a side. The chondrules and CAI’s are obvious as white bodies embedded in a dark black matrix. The insoluble organic matter exists in the dark matrix. This meteorite has, so far, defied classification beyond identifying it as a generic carbonaceous chondrite exhibiting type 2 alteration (i.e., an ungrouped C2 meteorite). We now know that this particular clast was signficantly altered, post accretion, by hydrothermal processing and yet some Tagish Lake IOM is nearly as pristine as what is seen in CR chondrites (Alexander et al. MAPS 2015).
One of the challenges in understanding the early evolution of the solar system involves establishing whether one can identify chemical signatures of these reactions encoded in the chemical structure of the meteoritic organic fractions and whether there exists any relationship between the molecular structure(s) of organic matter with the classic designations of meteorite group and type, e.g. the degree of alteration. One of the problems with addressing such questions is that between 70-99% of the organic carbon contained with carbonaceous chondrites is insoluble in any solvent. Thus, the classic molecular methods available for the study of complex organic assemblages (e.g., Gas Chromatography-Mass Spectrometry-GCMS) are not available.
In the beginning- my first introduction to IOM from the great Murchison CM2 Chondrite- A Great Fall
I set out to apply solid state Nuclear Magnetic Resonance (NMR) Spectroscopy as a primary method of deriving self-consistent and quantitative analyses of the insoluble organic matter (IOM) fractions obtained from carbonaceous chondrites. In order to this end we utilize a custom designed demineralization procedure derived by our colleague Fuoad Tera (DTM) that employs high molarity CsF aqueous solutions with the pH adjusted with HF to achieve nearly perfect demineralization. With these isolates I am able to apply solid-state nuclear magnetic resonance spectroscopy to thoroughly characterize the meteorite IOM. I have developed a protocol that employs 8+ independent NMR experiments to yield an internally consistent analysis of the essential molecular characteristics. These experiments are time consuming, however, and it typically takes about one month to completely analyze a given IOM fraction. I use these data as a means of comparing the IOM fractions from different meteorites in order to assess the role that parent body and other processes have modified IOM from its pre-solar or otherwise pristine state. Our first 13C Solid State NMR analysis was of Murchison IOM- I like to refer to Murchison IOM as the "ecoli" of ET IOM :) [see figure 4].
Figure 4 (Right): This 13C variable amplitude-cross polarization magic angle spinning (VA-CPMAS) NMR spectrum of the IOM from Murchison (a CM2 Chondrite) was our first clear chemical view of the complex structure of IOM. The spectrum reveals the enormous chemical complexity of extraterrestrial organic matter. Analysis is limited to designating specific spectral regions a likely reflecting the contribution from various functional groups, e.g. alcohols and/or ethers (CHxO).
We ended up doing a really wide range of experiments on this single sample and really were able to nail the key features of the complex organic polymeric material. The only thing we missed was only revealed when we set out to do the 2 dimensional MAT experiments (see below).
Next: A Comparison of Organic Matter From Four Different Meteorite Groups:
I have then completed a series of solid-state 1H and 13C Nuclear Magnetic Resonance (NMR) Spectroscopic experiments on isolated meteoritic Insoluble Organic Matter (IOM) obtained from four different carbonaceous chondrite meteorites; a CR2 (EET92042), a CI1 (Orgueil), a CM2 (Murchison), and an undesignated rank 2 meteorite, Tagish Lake. I find that the solid state NMR experiments reveal considerable variation in bulk organic composition across the meteoritic IOM fractions. For example, the fraction of aromatic carbon increases as CR2 < CI1 < CM2 < Tagish Lake (C2). These increases in aromatic carbon are largely offset by reductions in aliphatic (sp3) carbon moieties, e.g, CH3, CH2, CH grouped as “CHx”, and CH2O, CHO, CO grouped as “CHxO”. Oxidized sp2 bonded carbon, e.g. carboxyls and ketones grouped as “CO”, are largely conservative across these meteorite groups. Single pulse (SP) 13C magic angle spinning (MAS) NMR experiments reveal the presence of nanodiamonds in each IOM fraction with an apparent concentration ranking of CR2 < CI1 < CM2 < Tagish Lake. A pair of independent NMR experiments reveals that the aromatic moieties in all four meteoritic IOM fractions are structurally similar with high degrees of substitution.
I concluded from these data that both the aromatic moieties and nanodiamonds may have been unaffected by low temperature parent body processes and constitute inert markers of organic reaction progress. Fast spinning SP 1H MAS NMR spectra ( FIGURE 6) provide information on the fractions of aromatic and aliphatic hydrogen that when combined with other NMR experimental data reveal that the average hydrogen content of sp3 bonded carbon functional groups is universally low indicating a high degree of branching in each IOM fraction. Inspection of Figure 4 (below) reveals the enormous differences in the organic structure of IOM obtained from these four meteorites. The reduction in intensity at ~ 15-70 ppm corresponds to a loss in saturated organic carbon, CHx and CHxO. The apparent gains at ~ 129 ppm reflect a relative increase in aromatic carbon. As a product of our analysis, I have suggested that the aromatic carbon is inert under these parent body conditions and sp3 carbon is lost [to CO2(?)]: this is really an argument based on basic organic chemistry- my colleague Conel Alexander would prefer that sp3 carbon was converted to sp2 carbon and essentially no carbon was lost from IOM. This is also theoretically possible (see XANES below for such evidence). At this point we really do not know. Nor does it appear important. That is until you start to try to understand D/H variations with such processing. What we find is that D/H decreases linearly as the fraction of aromatic carbon increases- but you only see this clearly with the Tagish Lake Clasts- this is profoundly important.
Figure 5 (Right): These NMR spectra reflect ENORMOUS differences in the carbon chemistry of meteoritic IOM material spanning meteorite group. We believe that these differences reflect differences in parent body processing (see Cody and Alexander, GCA 2004 for the gory details). Note that this is just the “tip of the ice berg” of what solid state NMR is uniquely providing us. (Please see Cody et al. GCA to be published late 2004-earlier 2005)
These data led me to conclude that the dominant chemical reaction that yields these chemical differences involve either low temperature chemical oxidation or hydrothermal alteration during the earliest stages of parent body alteration. The Tagish lake IOM, evidently, suffered considerably more chemical oxidation or hydrothermal processing during parent body processing than did the CR2 (EET92042) IOM (Cody and Alexander 2005). As to the nature of the oxidant, the chemical modification of the IOM requires a fairly strong oxidant. My current best guess is that the oxidant was hydrogen peroxide, a likely constituent of the ices from which the aqueous fluids were derived. Hydrogen peroxide may have reacted with any Fe2+ in the system to form Fe(OH)2+ and hydroxy radicals •OH. Hydroxy radicals would have severely degraded the IOM fraction yielding chemical changes identical to those recorded in Figure 4.
FIGURE 6: Solid state 1-H NMR spectra of IOM from CR, CI, CM and TL chondrites. The 1-H NMR solid state NMR spectrum is much simpler than the 13C SSNMR spectrum and given various line broadening issues can only clearly resolve aliphatic hydrogen from aromatic/olefinic hydrogen. But that is actually a very important constraint when aiming to determine IOM molecular structure. These data were collected using our 2.5 mm rotor probe with moderately fast magic angle spinning of 26 KHz (really we spin these samples at 26,000 revolutions per second- blows my mind!). What you see is that evolving from CR - CI - CM - Tl, hydrogen moves from aliphatic dominant to aromatic/olefinic dominant. This parallels what we see with 13C SSNMR. Overall H is being lost and aliphatic carbon is being lost, while aromatic C and H are retained. It turns out that Tagish Lake ultimately confirmed (a decade later) what our Cody & Alexander GCA 2005 Study proposed from these meteorites.
Ok! we think we got it! Study of CM's from different falls and finds and ranging from petrologic type from 2 to 1- Nope! Back to work... more to learn!
Figure XX: 13C VACP NMR spectra of IOM from a variety of CM chondrites of type 1 and 2 petrologic type. Also included are the deuterium and 15-N abundances. What is striking is that the molecular structure of CM IOM is nearly identical across this suite of meteorites. It is interesting that the CM Bells has such anomolous enrichments in D and 15-N even as the molecular structure is very similar to all the other CMs. We are studying what D/H abundance actually means.
Note: After observing the this similarity in IOM structure amongst CM's and observing that our two CR2's EET92042 and GRO95770 also were similar to each other and distinct from CM's we began to believe that IOM molecular structure was a defining signature of chondritic group. Note that while CR2's and CR1's are distinct petrologically- like CM's the IOM looks very similar. This suggested that the concept of petrologic type 1 & 2 has no meaning for IOM molecular structure.
However, when the Tagish Lake clasts became available for study we were blown away to observe that within one object (the TL meteoroid- prior to breaking up) we observe CR-like, CI-like, CM-like and thermally altered IOM - all from one object! (see figure below).
Also, we find that the type 3 petrologica type IOM are completely different than type 1 and 2 (see below).
Yes- I have a lot of papers to write up here- I am working on this!
But the data I have collected is exquisite! I have NMR data on so many chondrites it swirls around me- "saying" publish us!
Yes I will!
Studying The effect of extensive thermal alteration on IOM in the type 3+ chondrites- WOW!
My interest in thermal metamorphism’s effects on IOM were initiated by an early NMR paper on IOM by Cronin, Pizzarello, and Frye (GCA, 1987); where they analyzed a partially purified IOM fraction of Allende. Remarkably, their sample appears to have substantial aliphatic carbon (CHx), in spite of the numerous reports of Allende being subjected to moderate heating (e.g. up to ~ 530 °C). The problem is that Allende has, relatively speaking, only a small amount of organic carbon (~ 0.2 wt %). It took Conel Alexander a considerable time to isolate Allende’s IOM fraction (approximately 3 months of repeated treatments and washes) with a yield of ~ 35 mg of nearly pure IOM. We were fortunate to also receive a sample of Y86720, a well studied thermally metamorphosed CM chondrite. According to some in the literature, the mineralogy of Y86720 may record peak temperatures of up to 850 °C. It turns out the acquiring 13C NMR spectra was also not so simple...
Whereas it was an enormous challenge to obtain organic matter from Allende, it turned out that acquiring NMR data on this sample also provided a significant challenge. After numerous attempts I could obtain no signal when using acquisition parameters that were optimized for all previous IOM NMR studies. I came to understand that both Y86720 and Allende IOM are distinctly different from other meteorite IOM fractions and have now optimized the NMR acquisition parameters to analyze these. What I discovered (the trick!) was quite remarkable- I found I had to treat IOM in Allende and Y86720 as matter behaving like an organic conductor(!)- study of why this is so was published in 2008 (see Cody et al. EPSL 2008). I discovered that primitive IOM when subjected to high temperatures in the laboratory (under Argon!) slowly transforms into graphene- an organic conductor.
We (Me, Hikaru Yabuta, and Bjorn Mysen) subsequently performed experiments to derive a phenomenological kinetic expression for this transformation that can be used as a Cosmo "thermometer". First from 13C NMR we observe upon progressive (and apparently homogenous) transformation to graphene- evident in a progressive "negative" knight shift in primary aromatic carbon resonance (Figure 7). More significantly, however, we discovered via C-XANES that there is a progressive growth in a graphene diagnostic feature - the 1s-sigma* exciton peak at 291.6 eV (FIGURE 8) . Our kinetic expression (Cody et al. EPSL 2008) was used to put effective Temperature max's (see paper for details- basically a isothermal high T "bathtub ring"- see paper!) assuming 10 million years of parent body heating. What we find is largely what the cosmochemical/meteorite community agree upon (SEE FIGURE 9- Exciton intensity vs. Teff- Cody et al. EPSL 2008).
Figure 7: Wait!!!! This is not boring! Yes it looks like a broad peak moving right for some reason. So let me explain to you why it was amazing. Having done 13C SSNMR on organic solids, coals and other things for ever (well since Ph.D. in 1992), I and everyone sees and expects to see 13C in aromatic environments via NMR resonating at a 13C frequency of 130 ppm (relative to std. TMS). So when I finally got a 13C NMR spectrum on Allende IOM I saw that it was very broad and shifted to a frequency of 115 ppm- this was crazy!!! Tagish Lake, mostly aromatic carbon was dead on at 130 ppm, but Yamoto 86720 a thermally metamorphosed CM was shifted to lower frequency, and Vigarano a CV3 chondrite had its aromatic C resonance at even a lower frequency- WHAT WAS GOING ON! It turns out that this is a paramagnetic shift due to conduction band electrons in graphene- Carbon in Allende behaved like an organic metal! We later discovered a more Graphene like characteristic of Allende IOM and used this to derive a Cosmic thermometer. (see below).
This thermometer first published in 2008 remains robust at this writing of 2018. Some like it and some don't. I learned from this experience that sometimes your ideas are not always popular.... but that is OK- because you still have to explain the data- meaning why is Allende IOM shifted from Tagish Lake by 15 ppm in frequency- this you cannot ignore! Whatever your Allende story- it has to tell you that IOM in Allende is an organic metal- that is a fact!
But, I think that data are key and ideas are key, so lets release these and apply the best logic, science, to determine the best ideas.
Figure 8 A C-XANES Spectra of type 3 IOM isolated from CO, CV, Ordinary Chondrites, one Enstatite chondrite (Indarch) and natural graphite. It was known since 1993 that graphite exhibited a novel electronic feature on its carbon K-edge that was shown to be a 1s-sigma* exciton- that is a signature of "graphene". We were excited when we identified the presence of the 1s-sig* exciton in type 3 IOM. We noted that the exciton apparently grows into the C-XANES spectrum- best seen in the 1st derivative of the C-XANES spectrum (B). We were able to use this feature as a cosmo-thermometer!
Figure 9: The correlation of Normalized 1s-sigma* exciton intensity with Effective Isothermal temperature. Curve A is derived from the laboratory kinetics - which predicts temperatures that are clearly too high! Curve C is determined assuming that Allende was never heated above 350 °C - which clearly predicts temperatures too low! Curve B was constrained by an independent effective temperature for Isna (CO 3.8 of 705 °C). Curve B sweeps through many previous temperature estimates for condrites and in the case of Indarch predicts a temperature that is below the temperature of initial melting (~ 1100°C. See Cody et al. EPSL 2008 for more details. The most distinct outlier is Bishunpur where temperature estimates have been low, however, Allende has also been estimated to have been subjected to temperatures ranging from 350 °C up to 600 °C. The exciton thermameter predicts Allende was subjected to an effective temperature of 560 °C for considerable time.
The amazing Tagish Lake Clasts- All primitive IOM in one primitive object- The Rosetta Stone for meteorites? I think this might well be so.
Compositional Variation of IOM Accompanying Hydrothermal Alteration: type 1-2 All CM.
- We are finished with our analysis of a suite of 7 CM chondrite IOM fractions with varying degrees of hydrothermal alteration (petrologic type 1-2). We were fascinated with the idea that that like the variation of IOM molecular structure across meteorite groups (see figure 4 above) would also be reflected across a single group (e.g. CM with a full spectrum from petrologic type 1 to 2). As you can see in Figure 9, we observe virtually no difference in IOM molecular structure with petrologic type amongst the CM group. This was nearly a years worth of work (still not properly published) and a startling negative result.
- While we puzzled this lack of any significant variation amongst CM's (Figure 9), we several years later were invited to study the new released Tagish Lake Clasts. These were the amazing samples that were collected from the Tagish Lake and remained frozen by an individual until the Canadian Government bought these for study (THANK YOU CANADA; I believe that these samples are the "Rosetta Stone" of chondritic IOM). Working under the Lead of Chris Herd (U. Alberta) we discovered that within a single extraterrestrial object (~ 10 m in diameter) there was the full range of IOM alteration that we observed across all primitive meteorites (see Figure 4 - above) (FIGURE 10- CONEL REVIEW ARTICLE With TL comparison with other groups IOM NMR HERE).
Figure 11: A compilation of type 1 and 2 (not 3 IOM) samples- (trust me type 3 IOM is a whole different beast and one that I will be addressing soon!).
On the left are 13C NMR spectra of IOM from different meteorites that are clearly different based on degree of parent body alteration. Top most pristine, bottom most hydrothermally altered.
On the Right are 13C NMR spectra of IOM from different clasts from one meteoroid- now meteorite- that span the range of IOM chemistry we see on the left- THIS IS REALLY AMAZING! This is why I think that the Tagish Lake Clasts are possibly the "Rosetta Stone" for primitive IOM.
What we see is that the organic solids isolated from the Tagish Lake fragments (from an intact body that exploded in the Earth's atmosphere)- span almost the entire range of molecular structure of type 1-2 IOM from any meteorite group. This is really important. We never expected to see this- so what it means is that contrary to what we saw above with regards to CM IOM- IOM can vary considerably within a given parent body. So while our CR's look a like and the CM's all look a like- this does not mean that IOM molecular structure can speak definitively to something regarding CM, CI, CR, ... etc. planetesimal history- there is much going on here that is not at all understood!
We are at the verge of understanding what IOM molecular structure means- but more work needs to be done- BTW, type 3 IOM is completely distinct from even heated-CM (like PCA). There is much more that needs to be learned- but much we have learned- Check out the Tagish Lake papers!
Organics in Comets! Our studies of Comet Wild 2/81P provided by the STARDUST Mission- Thank you NASA!
Analysis of Cometary IOM via Micro XANES (Closing the loop? and adding more questions)
- I and Hikaru Yabuta (now Professor at Hiroshima University) were pleased to be included to be included in the Stardust Mission Principal Examination Team. The capsule successfully returned to Earth in 2006 and in short order many of us were hot on the trail of cometary organics- the first captured for sure from a comet (note of course Interplanetary Dust Particles (IDPs) have been long considered to be sourced from Earth passing through Cometary tails (Spoiler- our analysis strongly supports this contention about IDPs).
Figure 12: Comets are widely considered the most primitive objects in the Solar System. It has been largely believed that comets condensed from the molecular cloud ~ 4.5 billion years ago and have largely been frozen remnants of molecular cloud material for the entire history of the solar system.
Figure 13: The STARDUST Mission was launched in 1999 and sent on a 7 year and 3.3 billion mile journey to collect partices from the Comet 81P/Wild 2. The mission was a total success and the sample capsule was successfully parachuted into a dry lake bed in Utah with the sample collector completely intact.
Figure 14: LEFT: an image through an aerogel collector highlighting a terminal particle that is clearly defined and very very small! RIGHT: My STARDUST analyzing partner Dr. Hikaru Yabuta (HIroshima University) behind the ground breaking "5.3.2" Scanning Transmission X-ray Microscope (STXM)- this end station is the model by which all STXM's are made [our excellent data could only have been obtained with incredible help and collaboration with David Kilcoyne!]. Note that the actual microscope is out of the picture on the right- but it is resides in a rectangular aluminum box so showing it hardly reveals anything. Dr. Yabuta is standing behind (her right) of the "nitrogen filter" - NOTE TO THE WISE: BTW, back in the day we all learned how important the N-filter is- MAKE SURE YOU DO!
Figure 16: LEFT: Of course what people are drawn to are the terminal particles- On the image left you see a cross section into an aerogel collector- particles came in from the left, there was an "explosion" yielding a "bulb" and then obvious tracks lead to terminal particles at the end of the entrance point- ~ 10 mm after impact. Now realize that the impact velocity was on the order of 6 km/second- so... the particle had to decelerate really fast: from 6 km/s to 0 in 10 cm! It is a wonder that anything could survive such an impact, but this is were the aerogel did a great job. RIGHT: A terminal particle that was microtomed to a thickness of ~ 150 nm. The first thing we did was "mapping", basically we take a pair of images, one on top of a given K or L edge and another just below the edge, the "map" is plotted as -log[I(above)/I(below)]- where brighter = more of element, black means none of the element. So on the right we show an Oxygen "map", Iron "map", and calcium "map" and then a three color composite where Oxygen is green, iron is blue, and calcium is red. Note, the tiny bright spots in the iron "map" are most likely FeS grains, beyond these there are two obvious grains one with abundant Fe and Ca and the other having less Fe and Ca (the big grain on top); we can guess that we are looking at enstatite (top) and CPX (bottom).
So why is this amazing? These are high Temperature phases that are expected to have formed relatively near to the sun, yet the comet 81P/Wild 2 is unambiguously a Kuiper belt object that has resided at an orbit at or beyond that of Pluto for likely most of Solar system history (~ 4.5 Ga). So these little high T grains must have formed in the inner part of the Solar system, were then cast out to the Kuiper belt and accreted into a cometary planetesimal that was (at some point) destroyed through planetesimal collision yielding multiple planetary fragments one of which was Comet 81P/Wild 2 that due to some gravitational perturbation was ejected from the Kuiper belt and launched in-ward towards Earth- achieving an orbit such that the NASA STARDUST mission was able to cross the comet's orbit and collect the samples that once brought to Earth were analyzed by Hikaru, David and me :)
For this particle we are talking about an incredible journey!
Figure 17: Left- So for us organics folks (Hikaru, David Kilcoyne and me), the organic particlaes seemed come from the "bulbs" [note this has not been systematically verified at all, but rather our initial experience] RIGHT: Examples of four organic rich STARDUST Particles- the particle (upper right) has an enstative grain in its core. Also note that whereas the particle images are made a single energy, the particle on the upper right is a carbon "Map". These are tiny particles, fortunately the STXM at ALS beamline 5.3.2 provides X-ray focus down to 30 nm so a micron is like a foot ball field.
Figure 18: LEFT C-XANES spectra of a range of organic rich STARDUST comet particles compared with A) a respresentative anhydrous Interplanetary Dust Particle (IDP)- thought be be comet derived, B) very primitive IOM from a CR chondrite [Note: in general we find that that organic matter in CR chondrites is the most primitive = least thermally altered, than any other ET organic solids]; C) IOM from the Allende CV chondrite- this is an example of an extensively thermally metamorphosed IOM. The various "peaks" labeled A-F correspond to various XANES "bound states", where A= aromatic 1s=π*, B= a 1s-π* of aromatic carbon bonded to a carbonyl (e.g. acetophenone), and so on...
On the RIGHT: we have used XANES (easy to do) to determine atomic O/C and N/C. What we found what that the STARDUST particles are enriched in oxygen and nitrogen relative to more thermally altered Chondritic IOM. Note that the O/C and N/C of the anhydrous Interplanetary Dust Particle IDP L2011R11 is similar to the two STARDUST particles.
We were intrigued as to whether there was an "evolutionary" trend linking comet/IDPs with chondritic IOM possibly due to the extent of parent body heating. If there were such a connection than this is a game changer, because many believe that the processes that make refractory solids in comets (from far from the Sun) had to be different from processes that made IOM in chondrites (near to the Sun).
Figure 19: Comparing C-XANES spectra from STARDUST particles with that of Murchision IOM (a fairly primitive carbonaceous condrite- Low temperature but fairly wet). The yellow square refers to high N/C and O/C, where the C-XANES is dominated with a single peak at ~ 289.9 eV that is diagnostic of C-O (sigma bond) that could reflect either alcohol or ether. The purple square is also a C-XANES spectrum from a STARDUST particle , but with lower N/C and O/C. Note that the ~ 289.5 eV peak is no longer predominant, two (actually three) new peaks appear at 285 eV (aromatic/olefinic 1s-π*), and 286.5 eV (indicative of an ene-ketone, observed in the decomposition of polysaccharides), and a peak at 287..5 eV (carboxyl 1s-π*).
The C-XANES data do suggest a chemical pathway from STARDUST organic solids to chondritic IOM, suggesting that inner solar system IOM shares a common origin with organic solids that formed in the Kuiper belt.
This is not at all an mainstream idea, but this observation got me interested in exploring the chemistry. The next observation (see below) was a 2D solid state NMR result that really upset the "applecart" with regards to IOM organic structure.
Meanwhile back to the IOM problem- PROGRESS!: Identifying a source/origin for IOM in primitive Solar System Objects: The First lab synth. of actual IOM-like organic matter.
Figure 20: The Magic Angle Turning (MAT) 2D solid state NMR experiment performed on Murchison IOM. We are looking "down" on a "contour" map of spectral intensity. This experiment reveals static chemical shielding powder patterns along the MAS dimension (horiz.) and the isotropic spectrum projected on the "evolution dimension" (vert). This experiment took a huge amount of time, but as B shows clearly worked! The cool thing was that this experiment clearly showed us that substituted furan moieties were abundant and substituted phenolic moieties were not. This was completely counter to what was expected based on canonical pyrolysis studies (see caveats about Py-GCMS- below) by Hayatsu, Anders and all back in the 1980's and was a really important clue as to how IOM might have formed as furans are most easily formed by hydrothermal rxn's of sugars and sugars most easily form from formaldehyde- an abundant molecule in interstellar ices. (Cody et al. PNAS 2011).
Note: This image was made using MacRMN software written and provided by Phillip Grandinetti
Figure 21: A schematic reaction pathway showing how starting with the formose condensation one can move to a complex suite of sugars and these can lead to a very complex suite of molecules including highly substituted furans, branched and cyclic alkenes, and ultimately small highly substituted aromatics as have been shown to be the key to primitive IOM chemistry. The key is that, however IOM is made, the reactions have to occur at moderate temperatures, must be spontaneous, and most lead to considerable molecular complexity. The scheme shown on the left has this potential and we have been studying this in detail to understand IOM synthesis better.
BTW: There is always a temptation to attempt to "draw" a cartoon "molecular structure" of what IOM molecular structure might look like. The same was true for coal and kerogens (type I, II and III). In my view such an attempt is a mistake and is bound to fail. The reason is that IOM structure is way too complex (you would need at least 10,000 or more individual carbon atoms) to be included in a such "cartoon" and the structure is obviously a three dimensional structure in any event.
So I challenge anyone confronting a cartoon of IOM molecular structure: Ask whether this cartoon actually an accurate representation of primtive IOM? How constrained are the specific functional groups as are defined. What exactly is the cartoon telling you?
I will not make such a cartoon- it is not informative, it provides no predictive value, and is not an accurate representation of IOM. The generalized reaction pathways on the left will lead to all the complexity that you do see in IOM and for me that is a sufficient and informative description.
Figure 22: So if we are correct about formaldehyde being the source of IOM we should be able make in the laboratory starting with formaldehyde (and glycolaldehyde). So we try it and it works really well. 13C solid state NMR spectra compares IOM from Murchison (CM2) with organic polymers we made in the laboratory. Sample F50 was synthesized at 50 °C and looks different. However, sample F250-4 (250 °C 4 hours) is starting to look very similar (not identical) but close to Murchison IOM at the functional group level. This is, as far as I know, the only laboratory synthesis that looks chemically like actual IOM. For example, UV-photolysis experiments of interstellar ice analogues yield an organic polymer ("goo") that when interrogated by C-XANES looked nothing like primitive IOM. (see for example Neuvo et al. Adv. Space Science 2011). From a perspective of organic chemistry the only two molecules that are both reactive and abundant in interstellar ices and cometary ices are formaldehyde and HCN. We already know that HCN polymer looks nothing like primitive IOM at the functional group level (13C NMR and C-XANES) and at the elemental level (atomic CNO).
Figure 23: Basically, whereas 13C NMR makes the connection between laboratory "IOM" and natural IOM, C-XANES of laboratory synthesized IOM looks nearly identical to organic solids in Interplanetary Dust Particles (IDPs) thought to be derived from comets. Laboratory "IOM" = F50 and F250, whereas as IDP organic solids are in column B. Looks like pretty convincing - but has some really interesting implications for our Early Solar System History!
Figure 24: On the left (A) we have have little organic "micro-balls" (scale bar = 1 µm) that were made by Dr. Yoko Kebukawa from hydrothermal rxn's with formaldehyde. On the right we have little organic "micro-balls", well ball (scale bar = 1 µm) that was made by nature and resides in an ordinary chondritic meteorite. Yoko showed that that little organic balls that she make are hollow and the focused ion beam mill showed that the natural organic ball in the ordinary chondrite is hollow. So, if the molecular chemistry of formaldehyde polymer is essentially identical to natural IOM and the physical morphology of laboratory analogue IOM is very similar to nature extraterrestrial IOM, then you would think that this would be pretty solid evidence of a connection and support for the idea that interstellar formaldehyde trapped in interstellar ices and carried into accreting planetesimals might be the origin of the Solar Systems greatest reservoir of primitive organic carbon- well I do, but the cosmochemical community is a pretty skeptical bunch of folks and many really like the idea that organic solids were made through UV photolysis at very low conditions... more work needs to be done to convince all parties that shape matters and smooth-hollow microballs can't form at 20 - 120 K in interstellar ices.
C-XANES: Powerful, but subtle- Lessons needed to be learned by all.
Figure 25 (Right): Carbon Near Edge X-ray Absorption Spectroscopy of Insoluble Organic Matter derived from four different carbonaceous chondrites. Note the systematic differences in the intensity of various 1s to bound-state transitions that correlate with the chemical differences observed via solid state NMR. NOTE: The aromatic 1s-π* transition does not get more intense (see 13C NMR spectra above), rather, becomes broader- this pretty much tells you that the aromatic structure is being modified from CR2 to TL; likely in the direction of polynuclear aromatic carbon growth. This would strongly suggest that my previous assumption of aromatic carbon being a "neutral" remnant of parent body processing can't really be completely correct. Rather the nature of aromatic carbon is being modified moving from CR2 to TL (and within the Tagish Lake meteorite, from clast 5h to clast 11v- see Tagish Lake papers). What I mean is that if the ∏ systems become larger then the number of ∏* states will increase shifting absorption intensity to higher energies...
C-XANES is a very powerful ultra-micro analytical technique. However, the key Near Edge features- e.g. various 1s-π* transitions - can vary subtly in intensity if compared to a molecular spectroscopy like 13C solid state NMR. For example in the figure above we show C-XANES spectra for the same IOM samples that we showed 13C NMR data above (See Figure __); where as 13C NMR data reveal a very big change in the intensity of the aromatic carbon resonance at ~ 130 ppm, the intensity of the 1s-π* intensity variations are more subtle. As another example please compare the 13C NMR spectrum of the formaldehyde polymers F50 and F250-4 above with the C-XANES spectra of the same organic solids just below (it is clear that the very significant differences in molecular structure evident in the 13C NMR are much more subtle on the carbon K-edge). Finally see C-XANES below - where things are are simpler.
Figure 26: So here is a simple example [well not so simple :)] of a system where the aromatic carbon increases as other carbon types (in this case sp3 carbon as alcohol in the form of cellulose and hemicellulose) accompanying fungal degradation of spruce wood by the "brown rot" fungus - Postia Placenta. Over a span of 8 months almost all of the polysaccharide is consumed by the brown rot fungus leaving the largely aromatic carbon rich biopolymer Lignin remaining and essentially unaffected (which is amazing!!!!).
So you see a progressive increase in aromatic carbon 1s- π* intensity at ~ 285 and 287.2 eV (reflecting an increase in lignin concentration relative to cellulose and hemicellulose.
The key here is that the lignin structure has not changed at all, only polysaccharide is being selectively removed by the fungal organism.
Compare this with the C-XANES of CR-CI-CM and Tagish lake above, where 13C NMR shows a huge difference in aromaticity (Fa) but no obvious increase in aromatic 1s-π* intensity- THIS IS REALLY IMPORTANT IF YOU DO C-XANES.
NMR is much easier to interpret than C-XANES; I find that C-XANES is very often miss-interpreted :
PLEASE DO NOT "BLACK BOX" C-XANES !
Or really anything- spectroscopy is not best done without understanding.
ELEMENTAL ANALYSIS OF IOM: Predominantly an Alexander and Fogel Story! Check it out! If you are into H/C, O/C, and N/C- go to Alexander et al. 2007 and 2010- it is all there- you will be satisfied :)
Elemental Analysis and Stable isotopic Abundances
- With Conel Alexander at the lead and In collaboration with Dr. Marilyn Fogel then at the Geophysical Laboratory (now at UCal Riverside) comprehensive H/C, O/C, and N/C data was well as dD, d15N, d13C, and d18O on nearly 100+ IOM fractions has been determined and it is clear that there is no simple story here. But there is a lot of data!
Figure 27; JUST ANOTHER REMINDER THAT IOM IS NOT KEROGEN! a comparison of O/C (Y-axis-blue), N/C (Y-axis Red) vs H/C (X-axis) variation amongst some IOM samples and some coals (type III kerogens). In both cases metamorphism pushes samples towards the origin. It is clear that "metamorphic" trends of IOM and type 3 kerogen follow very different trends with regards to O/C (blue)- Is this due to differences in molecular chemistry or is this due to process. I believe it is "process", specifically I believe that the striking reduction in O/C in type III kerogen may well be mediated by deep basin microbial action- obviously such would not affect any such change with IOM (no bio!)- hence the retention of high O/C across a range of H/C.
NOTE: N/C and O/C appears invariant with H/C. I have check this out, but this trend is more for less metamphosed IOM, at lower H/C, N/C definitey begins to dive. So the four meteorites platted here are the same CR- CI - CM and Tagish Lake samples. We are working on this!
UPDATE: See the N/C vs T(EFF) °C correlation below where you can see that N/C does in fact dive (with the Type 3 chondrites) to very low values.
Figure 28: During the 2017 LPSC Conference I presented a talk on the peculliar nature of nitrogen in extraterrestrial organic matter. What Nitrogen is doing in IOM is really peculiar and we are still working on it (We being Dionysis and Conel).
In the course of setting up the discussion I realized that Marilyn and Conel had collected bulk elemental data on many of the meteoritic IOM that I had made T(EFF) estimates, so I could see if there was any correlation between N/C and temperature. On the left is what I see. BTW, the red points are experiments that Dionysis did completely independently.
Interestingly the lone Enstatite chondrite (Indarch EH4) has the highest T-EFF and the lowest N/C - not far from what is estimated for Earth- at least by Bernard Marti (I think that Alex Halliday would like much more nitrogen - which would be in variance with what we see here- but more work likely needs to be done. This is where we are now.
Lots to consider here.
And we are!
Pyrolysis GC-MS of IOM: Great tool but complex Information and chemistry!
Figure 29 (Right): Pyrolysis-GCMS selected ion chromatograms highlighting the relative distribution of alkyl aromatics, phenol, and naphthalene/alkylnaphthalene. There appear to be Qualitative trends in molecular structure are revealed in these pyrolysate data. These data clearly point to some interesting chemical trends and these should be followed across all meteorite groups! Yet to be done! However, I really have no explanation as to why Allende select Ion chromatograms look like they do relative to the CR-CI-CM- and TL IOM. Based on subsequent 13C NMR and C-XANES clearly show is that Allende (CV 3.5+) IOM is completely different structurally from any petrologic type 1 and 2 IOM.
Pyr-GC-MS data are hard to relate to actually organic molecular structure. It is NOT CORRECT to assume that simple molecules in pyrolysate have anything to do with "monomers" in a classic polymer sense.
Pyrolysis Gas chromatography and Mass Spectrometry (Pyr-GC-MS)
- In addition to the analyses described above we have been analyzing our IOM samples with pyr-GC-MS. Pyr-GC-MS can provide a molecular fingerprint of meteoritic IOM requiring less than 1 mg. of sample. The data derived from pyr-GC-MS is complicated by the fact that one detects the stable products derived from rapid heating in a helium stream. The molecular distribution so derived cannot readily be re-integrated to derive a quantitative picture of the extraterrestrial macromolecule that is IOM. What you see is the stablized compounds that make it out of the pyrolysis process. If you note the apparent H/C of the pyrolysate you will see that it is much higher than IOM, and as only 30 % of IOM makes it to pyrolysate (70 % chars and goes nowhere), it tells you that the "char" is very H-depleted. Thus pyrolysis- GC-MS involves very strong H-C disproportionation: not a minor fact when interpreting things.
- We have been developing an approach wherein we can use pyr-GC-MS data to define a compositional space where in trends in IOM evolution with parent body processing can be revealed. However, In the case of primitive IOM, over 70 % of the pyrolysate is ignored by researchers because if falls in to the category of Unresolved Organic Matter (UOM) aka "humpane". When you look at characteristic mass fragmentation data of IOM "humpane" one observes considerable molecular complexity- Much work needs to be done here. We are working on it!
Figure 30: Typical pyrolysis GC-MS Total ion chromatogram (TIC) of Murchison IOM T = 615 °C 10 secs, heating rate 500 °C/second. What one observes numerous sharp peaks corresponding to simple compounds (e.g. naphthalene) over riding a broad featureless continuous elution of complex molecules (aka unresolved organic matter, UOM, or "humpane"). This "humpane" actually constitutes 70 + % of the pyrolysate and is generally ignored (which is not a correct thing to do). Note that Naphthalene while so prominent is less than 5 % of the pyrolysate. The mass spectrum of "humpane" reveals it to be likely hydroxylated and highly branched aliphatic molecules that due to their high polar nature do not separate well during chromatography. Note, that if you do slow pyrolysis, you might never see the humpane only the naphthalene, alkly-naphthalenes, alkyl phenols, ... etc.
Key Point: most of the pyrolysate from IOM is unresolved complex organic matter (the lump under the sharp peaks) that can't be ignored when attempting to intepret pyrolysis GCMS. You simply cannot ignore this!