Archive for the ‘Sikhote-Alin’ Category

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Meteorite show-and-tell at the PVAA September meeting

September 22, 2018

Last night was the September general meeting of the Pomona Valley Amateur Astronomers. Instead of having an outside speaker, we had meteorite show-and-tell. Members brought their personal collections of meteorites and impactites, or talked about their history with meteor-hunting, or both.

We kicked off with a short talk by Dr. Eldred Tubbs, who told us about his experiences working with the Prairie Meteorite Network when he was on sabbatical from Harvey Mudd in 1969-1970. The Prairie Meteorite Network was a program run by the Smithsonian Astrophysical Observatory between 1964 and 1975, which used a series of wide-format cameras scattered across the Midwest and Great Plains to capture images of bright meteors, in hopes of locating the resulting meteorites. In ten years of operation, the Prairie Meteorite Network only discovered one meteorite fall, the Lost City meteorite from just outside of Lost City in eastern Oklahoma.

We then proceeded more or less by size of collection. Our club secretary, Ken Elchert, only has one meteorite-related specimen, but it’s a doozy: a massive bilobed indochinite tektite the size of a small pastry. This blob of glass solidified in the atmosphere from molten material blasted out of a huge impact in southeast Asia about 700,000 years ago. I love tektites–externally they resemble black rock, like basalt, but in fact they are glass, so they only weigh about half as much as you might expect when you pick them up. Ken’s specimen, obtained from a gem and mineral show a few years ago, was easily the biggest tektite I’d ever gotten to see firsthand or touch.

Gary Thompson, our club treasurer, was up next. He presented two small meteorite specimens in nice cases. You can see them on the right side of the photo above, surrounded by books. I wasn’t taking careful notes so I don’t remember the details on the second, but the first, in the larger, wooden box, is a piece of an observed fall from 1918 in Russia.

Laura Jaoui was up next. She has an extensive collection of small specimens, including fragments of lunar and Martian meteorites and a couple of small pieces of the Chelyabinsk meteor that exploded over Russia in 2013. Laura also had a lot of cut and etched pieces to show the internal structure of meteorites, especially the beautiful Widmanstätten patterns inside iron meteorites. She had thoughtfully included a variety of magnifying glasses, jewelers’ loupes, and magnets for investigating the structure and properties of the samples in her collection.

I was next up, with my little collection. I haven’t blogged about all of them yet. The Middlesborough meteorite is not the original–that’s on display at the Yorkshire Museum. My copy is a cast that I obtained this spring, which fired my interest in oriented meteorites. I hadn’t known that such things existed, and I spent a few evenings educating myself about them. I put the results of my research into a slideshow, which I gave for the club late this spring, and later turned into the photo book shown here with my meteorites. In the time since I blogged here about my pieces of Campo del Cielo and Sikhote-Alin I’ve obtained additional, smaller representatives of both falls. The NWA Saharan chondrite I got on eBay earlier this year, and the tiny fleck of Canyon Diablo is from the gift shop at Meteor Crater. I picked up the moldavite in the center at a rock shop in Arizona last year. I do intend to blog about all of these things in time.

The anchor of the evening and the star of the show was Jeff Schroeder’s collection. Jeff has been finding, collecting, classifying, and working with meteorites since the 1970s, and he’s worked with some of the pioneering SoCal meteorite hunters. Almost everything on the long table in the above photos is his, and that’s only a fraction of his collection. Jeff gave us a wonderful talk on the history of the collection–much of which is bound for local universities in time–and on the histories of the specimens themselves, and what they tell us about the history of the solar system.

All in all, it was a great evening, with lots of great specimens and inspiring conversations. We should do more things like it in the future. The 50th anniversaries of the Apollo missions are coming up, and we’re planning to have members give short talks about each manned Apollo mission in the month of its 50th anniversary. But we should have a night next year just for people to bring their memorabilia of the space program. We have a lot of retired aerospace engineers in the club, including people who worked on the Apollo missions and the Space Shuttle. It would be great to hear about these things firsthand.

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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.