Archive for the ‘My meteorites’ Category

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My meteorites: Sikhote-Alin shrapnel (186g)

April 30, 2018

This is one of my favorite things: a piece of shrapnel from the Sikhote-Alin meteor that exploded over Russia on February 12, 1947. I picked it up at RTMC a couple of years ago.

I love it because it looks exactly like what it is: a wrecked piece of iron, fractured with the rest of its parent body from the core of long-destroyed planetoid, blasted asunder in the atmosphere in a multi-kiloton airburst, and finally shattered against the bedrock of the Sikhote-Alin mountains in far eastern Siberia. Every surface bears witness to the awesome energies of its birth, unleashed in a chain of events that we can barely comprehend, and certainly could not survive.

It fits perfectly in the hand, inviting you to run your thumb over its cracks, pits, and twisted, jagged edges. It has a satisfying heft, befitting a solid chunk of metal. It is 93% iron and 6% nickel, with small amounts of cobalt, phosphorus, and sulfur, and bare hints of germanium, gallium, and iridium. At room temperature it feels cold to the touch, as if it somehow still holds the chill of space.

I like to pass it around and have people handle it. With its weight, seemingly unnatural coolth, and textures that so clearly tell the story of its creation, it’s a fantastic hand specimen. I like to hold it myself, and think about the billions of years it spent in space. It was floating around out there while our ancestors attained multicellularity, backbones, limbs, amniotic sacs, hair, bipedality, fire, agriculture, writing, telescopes, powered flight, and the ability to split the atom. And then our paths crossed, quite literally, when the trajectory of the Sikhote-Alin meteoroid intersected that of Earth.

The energy released by the airburst of the Sikhote-Alin meteor is estimated at 10 kilotons (for comparison, the Chelyabinsk meteor in 2013 was about 500 kilotons). In all the long history of Earth, such large explosions had been the exclusive province of volcanoes and asteroid and comet strikes. But the Sikhote-Alin meteor entered a new world, where its 10-kiloton detonation was only the sixth largest explosion on Earth in the preceding 20 months, behind the atomic blasts at Trinity, Hiroshima, and Nagasaki in 1945, and the Able and Baker tests at Bikini Atoll in 1946 (all between 16 and 23 kilotons).

It is hard to think about such things, so removed from us in time, and from the scale of our experiences. I hold this cold piece of sharp-edged iron and think about all of the other Sikhote-Alins, Chelyabinsks, Tunguskas, and Chicxulubs out there, any of which might cross our path at any moment, and some of which inevitably will. In the words of the astronomer Kevin Zahnle (quoted in Seeing in the Dark by Timothy Ferris), “a day will surely come when the sheltering sky is torn apart with a power that beggars the imagination.”

Because it is only a matter of time until Earth is threatened with a civilization-ending or mass-extinction-level impact, is is also only a matter of time until we stop thinking of astronomy as the niche preoccupation of a few, and start realizing that it is an unavoidable aspect of our survival.

We need reminders of that fact. This one is mine.

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My meteorites: Campo del Cielo (40g)

April 25, 2018

My recent talk on impacts and the end-Cretaceous extinctions reminded me that I’ve never posted about my meteorite collection. It’s not a large collection, just a handful of things I’ve picked up, but each is satisfying in its own way.

This is the first meteorite I ever owned, a 40g piece of Campo del Cielo from Argentina. It’s about the size of the last joint of your index finger. Following the universal standard for meteorite photography, the scale cube in the photos is 1cm.

I picked this up probably 15 years ago at an auction at a Society of Vertebrate Paleontology annual meeting. I don’t remember the year – early 2000s for sure. The meteorite came with a little drawstring bag made of red felt, and a certificate of authenticity. It was clearly marked as a chunk of Campo del Cielo, which fell over northwest Argentina four or five thousand years ago.

The original Campo del Cielo meteor exploded in the atmosphere, much like the Chelyabinsk meteor over Russia in 2013, but on a much grander scale. The Chelyabinsk meteor is estimated to have been 20m in diameter, and it produced an airburst of approximately 500 kilotons. The Campo del Cielo meteor was probably more like 50m in diameter, so it would have been a multi-megaton explosion in the upper atmosphere. The resulting strewn field is 2 miles wide, more than 11 miles long, and includes at least 26 craters with diameters of up to 100 meters; the impact of the fragment that produced the 100-meter crater would itself have been multi-kiloton event.

I didn’t know any of that at the time I got the meteorite at the auction. I vividly remember how much I paid for it: $80. I remember so clearly because I almost instantly regretted it. I don’t know who I was talking to afterward, but someone looked at the meteorite and commented that it would be easy to fake with a bit of iron slag. That seemed plausible – it didn’t look like any meteorite I’d seen pictures of, so I assumed the chance that it was a fake was high. I had other fish to fry at the time, being a new dad and halfway through a dissertation, so I never did any research to see if the meteorite was real or fake. I kept it, but I never put it on display, and over the years I sort of lost track of it.

I rediscovered it this January during a major bout of house-cleaning. It’s funny, in the time between when I obtained this piece and now, I’ve looked at so many meteorite photos that I can just glance at this and think, “Yep, it’s a Campo”. Five minutes of image searching for Campo del Cielo pieces will turn up many authenticated examples with the same general appearance, like angular chewed gum with fracture lines and surface pitting. Campo del Cielo is one of the least expensive meteorites to obtain, with prices around $1/gram still being pretty common. (So in fact I overpaid a bit back when I got this, but since it was an auction to support the society I don’t mind.) With such distinctive morphology and such low prices, it’s probably much less expensive to simply buy a real piece of Campo than to fake one, especially at small sizes.

So even though it is one of the smallest pieces in my collection, this little gem means a lot to me. It tells two stories: one about my personal journey from interested-but-ignorant space enthusiast to semi-knowledgeable, semi-professional astronomy writer – and one about a 65,000-ton chunk of iron from the core of a shattered planetoid, which exploded with the force of an entire nuclear arsenal and showered a vast area with what must have been a lethal rain of shrapnel, from pea-sized up to house-sized. Including this little piece, cosmic voyager and witness to awesome forces of creation and destruction.

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If you’re interested in obtaining a meteorite or starting a collection, I have two pieces of advice. The first is, buy from reputable dealers. Many honest dealers are members of the International Meteorite Collections Association and will list their IMCA member number wherever they do business. There are good dealers who are not IMCA members for various reasons – some just don’t like clubs and the politics that sometimes comes along with membership – but it’s a start. Also check seller feedback if you buy from online markets like eBay. And use search tools to do quick checks on individual dealers; the meteorite collecting community is pretty vigilant about detecting and outing bad actors.

The second and probably more important guideline is to educate yourself. Spend a week of evenings looking through websites and online ads and learning to know what to look for in genuine meteors. It’s not completely foolproof – a few unscrupulous people will pick up bits of inexpensive recent falls and try to pass them off as examples of rare and valuable historical meteorites, for example – but at least you’ll develop the knowledge to tell genuine meteorites from “meteorwrongs”. Good hunting!

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A little piece of Mars

July 21, 2016

Mini Museum no 3614 DSCN1469

This is my Mini Museum: a collection of tiny samples of rare and interesting specimens from the history and prehistory of Earth and the solar system. There’s a lot of stuff in here that is very satisfying as both a paleontologist and an amateur astronomer. Highlights for me are the preserved woolly mammoth meat, the fiberglass casts of Diplodocus bones used as the Krayt Dragon skeleton in Star Wars: A New Hope, and, above all, the tiny piece of the Martian meteorite Zagami. It’s labeled “Martian atmosphere” because the meteor is known to contain tiny bubbles of Martian atmosphere in pockets of melted glass (Marti et al., 1995).

The specimens are embedded in a single block of acrylic that is 5 inches tall, 4 inches wide, and 1 inch thick. At $299 it’s not cheap, but it’s a pretty astounding collection of objects at any price. There is also a smaller, 10-specimen edition for $99. It doesn’t include Zagami or the Krayt Dragon, but it does have asteroid fragments, Stegosaurus plate, woolly mammoth meat, fulgurite, and the moon tree sample. These will sell out at some point, so if you’re interested in picking one up, don’t tarry.

Reference

Marti, K., Kim, J.S., Thakur, A.N., McCoy, T.J. and Keil, K., 1995. Signatures of the Martian atmopshere in glass of the Zagami meteorite. Science, 267(5206), p.1981.