An Article In Meteorite Times Magazine
Martin Horejsi's Meteorite and Tektite Books


 

NWA 2086:

The Mother of all CAIs

Is this the Largest Calcium Aluminum Inclusion in the World?*

*see below

large CAI

At the 2005 Tucson show, I had the wonderful but painful dilemma of choosing only one of two halves of an exceptional NWA individual for my collection. The teardrop-shaped specimen was sliced right down the middle lengthwise and each half held a portion of what I thought might be the most beautiful and largest CAI in the world. I studied each half carefully finally making my choice selecting density over surface area. But the decision always haunted me which might seem odd given the truckload of rare falls I acquired from Bob Haag that year.

Trapped within this individual of NWA 2086, a CV3 W1, S1 with a total known weight of only 780 grams, was a remnant of the birth of our solar system. And not just any remnant, but one visible from across the room! But I never forgot the other half, nor did I stop pursing it.

Perseverance Pays Off!

Almost three years later, hints of an chance to acquire the other half slowly materialized. Although it still took a few months of work, a bit of luck, a good friendship, and a pile of money, I can announce that today the halves are reunited once again. In case you are wondering, the mass of this pair of end sections is about one-fifth the entire total known weight of NWA 2086.

In this installment of the Accretion Desk, I would like to present some never-before-seen pictures of this cosmic masterpiece. And to those running other web sites, I give you permission to use the images of this stone as long as you include a photo credit as “Photo courtesy of Dr. Martin Horejsi” and if for online use, please link to this webpage at The MeteoriteTimes.com. Oh, one other thing. Please send me an email telling me where the picture(s) is/are displayed. Thanks.

CAI close up

 

from MacPherson, et. al. 2005 Chondrites and the Protoplanetary Disk. AASP Conference Series, Vol. 341

Calcium-aluminum-rich inclusions (CAIs) preserve a record of events in the earliest solar system, the timing of these events and the conditions under which they occurred.

Recent technical (analytical instrumentation) and theoretical advances have enabled researchers to extract an astonishing wealth of new information from CAIs, such as:

(1) all CAIs may have formed in a restricted region or regions near the protosun and then were transported radially outward to the various chondrite-accretion regions;

(2) the CAI formation “event” may have been very short in duration, possibly less than 105 years; and

(3) within the region(s) where CAIs formed, there were multiple isotopic reservoirs that experienced little intermixing.

 

vigarano

 

CAIs or Calcium Aluminum Inclusions were first described in the Vigarano carbonaceous chondrite in 1968 by Christophe Michel-Lévy. Ever since, they have long been a desirable feature in meteorites even after an abundance of them falling along with the rest of the amazing constituents of the Allende meteorite in 1969.

The above pictured 61g slice of Vigarano in the author's collection has several excellent CAIs. As if being the type specimen for the V in CV carbonaceous chondrites was not enough.

What is a CAI?

Rather than expounding upon the exciting science of CAIs, let me direct your to David Weir's comprehensive website where he details the complex nature of these geologic micronebulas trapped within their personal carbonaceous universe. Additionally, here are some links to a few great but somewhat information-dense articles about CAIs:

Calcium-Aluminum-Rich Inclusions Are Not Supernova Condensates

An Isotopic and Petrologic Study of Calcium-Aluminum-Rich Inclusions from CO3 Meteorites

Oxygen Isotopes Give Clues to the Formation of Planets, Moons, and Asteroids

Finally, here is a link to one of a small handful of scientific papers that address NWA 2086. Given the number of meteorite dealers who offer or have offered slices of the low TKW NWA 2086, I feel confident that my set of twins is in a class of their own. Of note, however, is a photo of a large CAI in NWA 2086 featured on the wonderful Meteorites Australia website.

Until this pair of end sections was found, the largest CAI I had seen of was barely a centimeter in any dimension, and I had heard of some a little larger. A few articles even pushed the CAI size range to "2-3cm" but I have yet to find someone who has actually seen one that large. In general, a large CAI is considered around five millimeters. These CAIs approach 25mm long and 15mm across, or 0.025 meters by 0.015 meters if you prefer.

CAI close up

 

CAIs are usually just described as white or gray and oval or round. However, this giant CAI needs an entire new set of adjectives including wispy, cloudy, forked, spiraled, nebulous, graduated, purplish, swirled, and budded.

In January of 2006, I presented my one-half of this stone to Mike Zolensky, a planetary scientist and curator of stratospheric dust at the Johnson Space Center. (read more here) Mike was thrilled when he looked closely at the specimen. But not because of the CAI. Instead, it was the fine grained matrix surrounding the CAI that tickled his fancy. I hadn't noticed it before, but if you look carefully at the matrix immediately surrounding the CAI, you will see a region of darker, extremely fine grained material buffering the CAI from the aggressive and distinct chondrule structure making up the bulk of this CV3.

The STARDUST Connection!

But the real exciting bit of synchronicity was that I showed the large CAI to Don Brownlee, the Principal Investigator of the STARDUST Mission, who later was studying CAI material from the second comet particle pulled from the aerogel collector grid!

 

Don Brownlee, the PI of the STARDUST comet sample return mission holds one half of the giant CAI in NWA 2086. The second comet particle studied from STARDUST was a CAI!

 

 

The Aerogel Collector Grid in the clean room of the Johnson Space Center just a few days after arriving back on earth.

According to Don Brownlee, "Many people imagined that comets formed in total isolation from the rest of the solar system. We have shown that's not true. As the solar system formed 4.6 billion years ago, material moved from the innermost part to the outermost part. I think of it as the solar system partially turning itself inside out.

"Truthfully, we really didn't expect to find anything from the inner solar system. Instead, it [the CAI] showed up in the second particle we looked at."

 

The polish on the two halves is different. Both were initially polished rather coarsely to highlight the chondrule structure. Before I acquired the second half, I polished my only piece to a sub-micron level using Tom Philips' equipment. We then inspected the CAI under his powerful microscope, but it was rather uneventful. Maybe in the future, we will continue our photographic search.

inverted color CAI

inverted color CAI

 

The above pair of color-inverted/black & white images provide alternate views of the complex nature of these CAIs. It is tempting to consider diverse forces causing the two CAI images to look differently. But as you know, they are just two surface cross sections of the same three-dimensional object. I wonder if an MRI machine could create a complete 3-D picture of the entire CAI?

 

Until now, it has been a fear of mine that I would never see the other half of this CV3 again. Even worse, I was worried that someone might acquire the other half never knowing the fate of its partner, or even caring. But unlike many meteorites whose sum of the sliced up parts sells for more than the whole, in my opinion, the owning these two complete halves together is worth magnitudes more than if each were sold separately.

NWA2086 exterior


Many of you might remember that my collecting focus is heavily weighted towards low-TKW historic falls. So why, after taking a year's vacation from writing the Accretion Desk would I return with a story about an NWA? Well, in the immortal words of the football legend Terry Bradshaw, "I may be dumb, but I'm not stupid."

Although this stone is a weathered hot desert chondrite, this specimen is truly a world-class example of beauty within, and a meteorite warmly welcomed into my meteorite collection as family.

 

 

The above YouTube movie shows the two halves in direct sunlight. The individual, even if uncut, would have made a nice display piece of this rare stone. But thankfully, someone wiser than I had the constitution to slice open the stone to see what was inside.

NOTE:

*In parting, I'm curious if this is CAI is indeed the largest in the world. The ruler shows the scale so if you know of any CAI as large or larger than this one, please contact me. Thanks.


The Accretion Desk welcomes all comments and feedback.

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