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Cometary Clues to Solar System Origins

The Earth receives thousands of tons of interplanetary dust every year as it makes its way around the Sun. Can we trace any of this material to a particular source? Scientists from the Carnegie Institution think the answer is yes, at least in the case of comet Grigg-Skjellerup. The Carnegie team worked with interplanetary dust particles (IDPs) collected by a NASA aircraft in 2003, just after the Earth had passed through the comet’s tail, focusing on the chemical, isotopic and micro-structural composition of the grains.

Collecting Comet Dust

A bit of background: NASA’s Scott Messenger (JSC-Houston) predicted that Grigg-Skjellerup dust grains could be captured in the stratosphere at a specific time of the year (the comet reappears every five years). The dust collection flights that followed his prediction involved an ER-2 high-altitude aircraft flown out of Dryden Flight Research Center in 2003. Out of this work came the new mineral now called Brownleeite, a manganese silicide found in one of the particles. NASA routinely collects IDPs in such flights.

comet_grigg-skjellerup

In the Carnegie IDP study, a particular signature seems to stand out. “What we found is that they are very different from typical IDPs,” says Carnegie’s Larry Nittler. “They are more primitive, with higher abundances of material whose origin predates the formation of the solar system.” That again points the finger at comet Grigg-Skjellerup, and it also offers the opportunity to study comet particles in the lab from more than a single comet. Recall that the Stardust mission brought back particles from comet 81P/Wild 2 in 2006.

Image: Comet Grigg-Skjellerup offers up material that is more than 4.5 billion years old. Credit: iStockphoto.

This is helpful stuff because comets are believed to incorporate matter from the Solar System’s formative era. We would expect such material to have escaped the heating and chemical processing that would have affected the planets, but interestingly enough, the Wild 2 dust included a great deal of altered material, as this news release points out. Grigg-Skjellerup’s dust tells us that all comets are not the same in terms of composition, giving us the chance, as Nittler says, to “…use them as tracers for different processes that occurred in the solar system four-and-a-half billion years ago.”

Cometary Differences and Similarities

We can also weigh the Grigg-Skjellerup material against the findings of the Deep Impact experiment on comet 9P/Tempel 1. From the abstract of the paper on this work:

Our study together with observations of comet 9P/Tempel 1 during the Deep Impact experiment and 81P/Wild 2 dust analyses reveal some compositional variations and many similarities among three Jupiter-family comets. Specifically carbonates and primitive organic matter or amorphous carbon were widespread in the comet-forming regions of the outer protoplanetary disk and not all comets contain as much inner solar system material as has been inferred for comet 81P/Wild 2.

Presolar grains — dust particles formed in previous star generations and in supernovae before the birth of the Solar System — provided the biggest surprise. They can be identified by their unusual isotopic compositions, but they’re normally quite rare. Yet in the dust particles associated with Grigg-Skjellerup they are tens of times more plentiful than in other primitive materials.

The paper is Busemann et al., “Ultra-primitive interplanetary dust particles from the comet 26P/Grigg–Skjellerup dust stream collection,” Earth and Planetary Science Letters, published online 8 October 2009 (abstract).

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Comments on this entry are closed.

  • MG Ellington November 5, 2009, 11:29

    “This is helpful stuff because comets are believed to incorporate matter from the Solar System’s formative era.” Does this mean that we expect they are older in many cases than our planets or of the same age? Do scientists expect that the material in these comets is a sampling of what is in many of the planets and/or their moons?

  • Adam November 5, 2009, 15:53

    Hi MG Ellington

    Comets preserve material that hasn’t been changed via the magmatism on and under the surface of larger bodies, like the planets and dwarf planets, which has effectively erased that very early history of the solar system from them. This isn’t to say that comets haven’t had a history of their own, but whatever formative heating they’ve experienced was minor compared to the large-scale lava/magma creation of the larger objects.

  • Carl November 5, 2009, 17:05

    Hello, MG,

    “The objects that did not accrete to form large enough bodies to differentiate retain the chemical composition of the original condensed solar nebula. Thus we believe the oldest meteorites (and comets, should we ever get to sample them) hold clues about the early phases of solar system evolution.” From http://lasp.colorado.edu/~bagenal/1010/SESSIONS/11.Formation.html ‘A Scenario for the Origin and Evolution of the Solar System’.

    The other thing that comets offer is fuel for fusion-powered craft: “Using deuterium as the rocket fuel of choice, abundantly available on the comets of the Oort cloud, rockets driven by deuterium fusion, can there be refueled.” http://arxiv.org/abs/0906.0740 which is a link from the Centauri Dreams October 26 article, “Refining the Deuterium Starship”, by Adam Crowl. By the time actual fusion starships might be built, astronomy could be able to verify cometary clouds around destination stars, potentially enabling them to visit several star systems.

  • kurt9 November 6, 2009, 17:30

    I’ve a question for you guys.

    I believe that cyano-bacteria is the most simple form of life that generates Oxygen as a by-product of photosynthesis. It is also the only such life form that is not a Eukaryote. My question is this: was the Cyano-bacteria that existed on the early Earth sufficient to create a Oxygen atmosphere that is breathable by modern life, or was the emergence of Eukaryote photosynthetic life necessary to create this atmosphere?

    I think this issue is relevant to the commonality of habitable planets in the galaxy.

  • ROCA November 7, 2009, 16:26
  • Administrator November 7, 2009, 19:21

    Thanks, ROCA. It’s now fixed.

  • ljk January 31, 2011, 5:33

    Extreme 54Cr-rich nano-oxides in the CI chondrite Orgueil -Implication for a late supernova injection into the Solar System

    Authors: Liping Qin, Larry R. Nittler, Conel M. O’D. Alexander, Jianhua Wang, Frank J. Stadermann, Richard W. Carlson

    (Submitted on 25 Jan 2011)

    Abstract: Systematic variations in 54Cr/52Cr ratios between meteorite classes (Qin et al., 2010a; Trinquier et al., 2007) point to large scale spatial and/or temporal isotopic heterogeneity in the solar protoplanetary disk. Two explanations for these variations have been proposed, with important implications for the formation of the Solar System: heterogeneous seeding of the disk with dust from a supernova, or energetic-particle irradiation of dust in the disk. The key to differentiating between them is identification of the carrier(s) of the 54Cr anomalies.

    Here we report the results of our recent NanoSIMS imaging search for the 54Cr-rich carrier in the acid-resistant residue of the CI chondrite Orgueil. A total of 10 regions with extreme 54Cr-excesses ({\delta}54Cr values up to 1500 %) were found. Comparison between SEM, Auger and NanoSIMS analyses showed that these 54Cr-rich regions are associated with one or more sub-micron (typically less than 200 nm) Cr oxide grains, most likely spinels. Because the size of the NanoSIMS primary O- ion beam is larger than the typical grain size on the sample mount, the measured anomalies are lower limits, and we estimate that the actual 54Cr enrichments in three grains are at least 11 times Solar and in one of these may be as high as 50 times Solar. Such compositions strongly favor a Type II supernova origin. The variability in bulk 54Cr/52Cr between meteorite classes argues for a heterogeneous distribution of the 54Cr carrier in the solar protoplanetary disk following a late supernova injection event. Such a scenario is also supported by the O-isotopic distribution and variable abundances in different planetary materials of other presolar oxide and silicate grains from supernovae.

    Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
    Journal reference: Geochimica et cosmochimica Acta (2011) 75:629-644

    DOI: 10.1016/j.gca.2010.10.017

    Cite as: arXiv:1101.4949v1 [astro-ph.EP]

    Submission history

    From: Liping Qin [view email]

    [v1] Tue, 25 Jan 2011 21:06:24 GMT (6847kb)

    http://arxiv.org/abs/1101.4949