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My meteorites: moldavite (2g)

October 4, 2018

I didn’t even know moldavites existed until last year. One of the highlights of my trip to the 3RF Messier Marathon in the spring of 2017 was seeing Jeff Barton’s meteorite collection. He set it out for us to peruse one day, and it covered a classroom’s worth of tables. I barely knew from meteorites back then–hadn’t caught the bug yet–but a few things stuck in my head. One was his collection of Chelyabinsk meteorites from the 2013 airburst. Another was his collection of tektites. I knew what tektites were in general, but I’d never seen any firsthand. Jeff had a really nice, good-sized moldavite and he encouraged us to hold it up to the light so we could see that it was translucent glass. I got a few snaps of that and I definitely remembered it.

A couple of months later I was driving back from a museum visit in Mesa, Arizona, with a colleague, and we stopped for lunch and gas. There was a rock shop across the street so I thought, “What the heck” and went in. Amongst the other treasures was this little moldavite in a little display case. I checked it out carefully–there is a burgeoning market for fake moldavites, but most are easy to spot as cast glass. All signs point to it being genuine, so I bought it as a souvenir of the trip.

Fifteen million years ago, a massive impact in what is now southern Germany created the Nördlinger Ries crater, which is 24 km (15 miles) across and still up to 150 meters (~500 ft) deep, despite considerable subsequent erosion. The impact scattered showered tektites over a vast area of east-central Europe, including parts of southern Germany, Austria, and the Czech Republic. Moldavites are typically green. They draw their name from the Moldau River in the Czech Republic, where the first pieces to be scientifically described were found.

This moldavite is one of my favorite pieces in my little collection. At outreach events I encourage people to hold it up to the light, and it never fails to impress. It’s strange, but satisfying, to hold a piece of glass 15 million years old.

Before I started reading up on meteorites earlier this year, I assumed that tektites must be pretty common, since they are impact glass from big meteorite impacts, and the Earth has had hundreds or thousands of crater-forming impacts in the last few hundred million years. But most known tektites can be traced to just four impacts:

  • an impact near southeast Asia or Australia, about 780,000 years ago, that produced the Australasian strewnfield (australites, indochinites, rizalites);
  • the Lake Bosumtwi impact in Ghana, about 1 million years ago, that produced the Ivory Coast strewnfield (ivorites);
  • the Nördlinger Ries impact in Germany, about 15 million years ago, that produced the Central European strewnfield (moldavites);
  • the Chesapeake Bay impact on the east coast of North America, about 34 million years ago, that produced a North American strewnfield (bediasites, georgiaites).

There are exceptions:

  • a Central American strewnfield in Belize, with tektites dated to 820,000 years ago, which only started to be reported in the 2010s;
  • Darwin glass, an impact glass associated with the Darwin Crater near the west coast of Tasmania, estimated to be about 810,000 years old;
  • Libyan desert glass from the eastern Sahara, inferred to be the result of an impact or airburst about 26 million years ago (strictly speaking, probably a surface melt rather than melted material thrown through the air).

If you know of a tektite strewnfield or impact glass site that I’ve missed, please let me know in the comments.

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My meteorites: Canyon Diablo

September 29, 2018

I only have a tiny fleck of the Canyon Diablo meteorite that created Meteor Crater in Arizona. And I didn’t even buy it myself–it was a gift from my friend Andy Farke.

I’ve been to Meteor Crater three times, and it’s been an amazing experience each time. In the gift shop, they have these little baggies for a few bucks with an info card and a little chunk of Canyon Diablo. Andy gave me mine years ago, and I bought one for my son, London, on our last visit.

If you’re wondering why the info card says “meteorite oxide”, it’s because the Canyon Diablo meteorite has been on and in the ground for a long time, and it’s had the opportunity to oxidize. Some of the iron oxide is hydrated iron(III) oxide, good old FeO, better known as rust, and I’ve certainly seen a lot of weathered Canyon Diablo specimens with a reddish patina of rust. But much of the iron oxide is iron(II, III) oxide, Fe3O4, better known as magnetite. Magnetite is black or dark gray, and I reckon that’s what I’ve got here, at least on the surface of this bit. I haven’t read enough to know if there might be unoxidized meteoritic iron in the middle, and I’m not going to tumble the specimen to find out!

My little piece of Canyon Diablo doesn’t look like much in the bag, but up close it has a surprising amount of character. I like it. It pays to not get too jaded about a piece of another world, no matter how humble.

Other posts in this series:

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Meteorites that bury themselves

September 27, 2018

I posted this in the “Space Rocks” forum on Cloudy Nights, but haven’t gotten any responses. If you have any relevant info, I’m all ears!

I recently got interested in oriented meteorites and I started reading up on some of the historically important examples, as well as some more recent finds. Some interesting trends are apparent:

  • Gross-Divina (shown above), July 24, 1837, observed fall, penetrated 75cm into the ground
  • Karakol, May 9, 1840, observed fall, penetrated 53cm
  • Kraehenberg (shown below), May 15, 1869, observed fall, I don’t know the penetration depth but it had to be dug up afterward
  • Middlesbrough, March 14, 1881, observed fall, penetrated 30cm
  • Cabin Creek, March 27, 1886, observed fall, penetrated 90cm
  • Adamana, possibly from July 19, 1912, Holbrook fall – I don’t yet know the circumstances of discovery but it might have been found on the desert surface
  • Baszkowka, August 25, 1994, observed fall, penetrated 25cm
  • Uasara, unknown date, possible observed fall, found on a path
  • Miss of the Desert, 2013, found on desert surface
  • Stromboli Stone, 2013, found on desert surface

There are of course loads of oriented individuals from other falls like Sikhote-Alin and Chelyabinsk, but these are the most strongly-oriented single stones for which I’ve found good information (if Adamana is a singleton and not part of the Holbrook fall). It may be a sort of wonky, artificial assemblage, but a couple of things jumped out: other than the ones that were found on the desert surface, all were observed falls that punched into the ground to a decent distance.

So it makes sense that the ones that weren’t found on the desert surface would be observed falls – if people hadn’t seen them fall, they might never have been found. I grew up in farm country and if you see a fresh hole only a few inches across you tend to think “varmint” and not stick your hand down there. Also, check out the dates – other than a couple in March, most were observed during the warm months of summer, when people are outside working. I assume that just as many highly-oriented meteorites fell in the winter months, or at night, and weren’t found because they weren’t observed falling and immediately buried themselves upon impact.

Does this same sampling bias affect non-oriented meteorites? I’ve only started reading about this stuff and haven’t gotten very far, but I’m curious if non-oriented meteorites from observed falls have had the same propensity for punching into the ground. Thanks in advance for any info, particularly for suggestions of books and resources I might check.

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My meteorites: Middlesbrough meteorite (cast)

September 25, 2018

This is the object that fired my interest in meteorites this year. Back in April, I gave a talk about meteorite impacts and mass extinctions at the Alf Museum. I took my little meteorite collection to have some hand specimens to show around afterward. The whole experience got me excited about meteorites, and I started doing some research online.

I don’t remember exactly what investigative chain led me to the Middlesborough meteorite, whether I found the cast on eBay first, or the Wikipedia article about it. Probably the eBay hit first, because it would never have occurred to me to search for it on eBay had I found the Wikipedia article first. Molding and casting of important specimens may be extremely common in my day job of paleontology (even just for fun), but it is not common at all for meteorites. Off the top of my head, I can only think of a handful of meteorite casts I’ve seen: the Middlesborough meteorite; the Stromboli stone, another oriented meteorite; and the flanged, button-shaped Australite tektites. A scale model of the gigantic Willamette meteorite, made available by Nakhla Dog Meteorites, also deserves mention here. I’m sure there must be more out there, but probably not a great many more.

In any case, the Middlesborough meteorite was my first encounter with the phenomenon of oriented meteorites: meteorites that maintained the same orientation as they were melted by their passage through the atmosphere, and came to be shaped like the nose cones or heat shields of spacecraft. Examples range from tiny, button-shaped meteorites 1cm in diameter to large meteorites weighing hundreds of pounds. Most of the best-known oriented meteorites were observed falls that happened during daytime and often in the summer months. I think there’s a very good reason for that: possibly because of their aerodynamic shapes, most oriented meteorites come cooking in at a several hundred miles per hour and bury themselves in the ground at depths from a few inches to a few feet. I assume that oriented meteorites fall just as often in darkness as in daylight, and in winter as in summer, but since most of them bury themselves, the ones that are seen impacting have a much better chance of being discovered, and there are more people out and about to see them in the warm months of the year. Especially in farm country (which statistically has a better chance of collecting meteorites than urban areas because there’s so much more of it), you don’t tend to go around sticking your arm down newly-observed holes in the ground on the off chance that there might be meteorites down there.

I didn’t know all this when I found the cast on eBay, of course. I did some comparing around, decided that the asking price was reasonable, made the purchase, and then set about educating myself about this new (to me) class of objects. Whenever I wrap my head around a new domain of knowledge these days, I like to crystallize what I’ve learned by putting together a slideshow on the topic. These slideshows serve two purposes: they help me remember what I once knew, the next time I circle back to that topic, and they help me introduce others to the subject. I spent a week of evenings reading up on oriented meteorites, made a little slideshow, which I presented at the next PVAA meeting, and then turned the slideshow into a photo book through Shutterfly. You can see the book amidst my expanding meteorite collection in the last post.

I will probably write more about oriented meteorites in the future. For now it is very satisfying to have a cast of the Middlesborough meteorite. I see that I’ve managed to write a whole post and hardly say anything about the history of the meteorite itself, its discovery, and subsequent studies. I’ll try to get to those things in the not-too-distant future.

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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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A planetary observing run on Mount Baldy

August 2, 2018

Last night I went up to Cow Canyon Saddle with some fellow PVAA members and other friends, for an informal star party. Venus, Jupiter, Saturn, and Mars are nicely lined up along the ecliptic right now, so we went to take a look.

I was rolling with London’s XT4.5 dob and my Apex 127 Mak. I hadn’t gotten the Apex out in a little over a year, and it was nice to confirm that it’s still in fighting trim.

Me, not so much. It was my first session with a scope – any scope – out in months, and I was a little scattered. I had to rifle through three bags to find my good diagonal, and it took three attempts to get out of the house with both my phone and my headlamp. The rustiness even extended to the sky. Normally I can get most of the good stuff using memory and dead reckoning, but I had to haul out an atlas to remember how to get to M81/M82 and M11. Sad!

I got up to Cow Canyon Saddle a little after sunset. Amanda and Ron Spencer and their kids were already set up, checking out Jupiter with their 90mm refractor. Ludd Trozpek was there, too, with a 10-inch dob. My friends and WesternU colleagues Thierra Nalley and Jeremiah Scott arrived a few minutes later.

Thierra, Jeremiah, and I started in Venus, which is in a half-full phase right now. We quickly moved on to Jupiter and then Saturn. Mars hadn’t cleared the mountains to the east so we spent some time running up the magnification on Saturn. The seeing was phenomenal. We put the 8.8mm ES82 in the Apex 127 for 175x and Saturn looked like it was nailed to the wall. We put in the 5mm Meade 100-degree and at 308x the seeing was visible, not as the usual small-scale shimmers, but as an occasional wave of distortion washing over the whole field of view, as if we were viewing Saturn through a thin film of water with a low ripple now and then. In my experience, nights on which I can push past 300x are few and far between, so we got pretty darned lucky.

Enough about the eyepieces and the conditions. The planets looked unreal. Even at low power, Saturn’s Cassini Division was easy and crisp, as if it had been punched out of the disc of the rings with a metal press. At higher power, the shadow of the rings on the planet and the shadow of the planet on the rings were equally stark. And the planet itself was striped with pastel bands of salmon and cream. We had no problem holding any of these details in direct vision. As always, it was a kick in the brainpan to be reminded that while I’ve been going about my little business on this little planet, Saturn has been doing its own thing out there, 800 million miles away: regal, immanent, undeniable. We caught Rhea and Titan, too, but failed to spot the other moons.

Jupiter was only slightly overshadowed by its smaller sibling. The King of Planets was wrapped in dozens of belts and zones, down to the limit of vision, with the four Galilean moons neatly arrayed to either side.

Of course, we had gone up in large part to look at Mars, and see if we could detect any details through the nearly-global dust storm. When Mars cleared the mountains to the east, it was instantly the brightest thing in the sky. Even Jupiter looked wan compared to the red planet. I think every scope on the mountain was aimed at Mars within the first minute. The seeing may have been good up high, but Mars was fairly boiling in the near-horizon turbulence. Still, we could see the north polar cap immediately.

We decided to let Mars climb up out of the murk, so we switched to the deeper sky for a while. Lyra was almost at the zenith and Epsilon Lyrae was an easy split at 175x in the Apex 127. We spent some time with the Ring Nebula while we were in that neighborhood, then swung north to catch M81 and M82 before they got too low. Then it was back to the band of the Milky Way to pick up M11, the Wild Duck Cluster (after the aforementioned faffing about) and Albireo.

We went back to Mars and the view in clear air was vastly improved. The north polar cap was steady, and we caught fleeting hints of detail elsewhere on the planet. I don’t think that was all imagination – the most recent Hubble images show some of the dark features in the southern hemisphere starting to emerge through the dust. We had fun, both with the observing and with teasing each other about Percival Lowell, canals, and Tharks.

Jeremiah had been keeping an eye on Cassiopeia as it rose in the northwest, and I was casting frequent looks in that direction as well. A little after 10:00 the Double Cluster finally cleared the local horizon and we got a nice look at 48x in the Apex 127 (as low as that scope goes, using the trusty 32mm Plossl). Our final object was the heart asterism around Sadr at the center of Cygnus, which I wrote about for the Binocular Highlight column in the July issue of Sky & Tel.

The Spencers had departed before we looked at the Double Cluster, and Thierra and Jeremiah left after Sadr. Ludd and I finished the session with a few minutes of binocular observing. He had along a recent acquisition: a WWII-vintage Sard 6×42 with a true field of 11.9 degrees. It’s a legendary instrument that lives up to the legend. The first thing you notice when you pick them up is that they’re heavy – there’s a lot of glass in there. That’s in part because the prisms are huge. Unlike some modern binos that skimp on prisms, the Sards have prisms that are if anything maybe a little oversized. The eye lenses are also immense. It’s not just a lot of glass, it’s good glass, as I could tell as soon as I looked through them. It’s not sharp to the edge – stars take on interesting shapes in the outer 25% or so of the field – but it is impressively sharp over a huge true field, with excellent clarity. It was an interesting experience, looking at all of the constellation Lyra at one time. Cassiopeia almost fits – you can see all but one of the stars at either end of the W/3/M. Ludd reports that under darker skies, the Sards are a wonderful tool for scanning the Milky Way. They’ve re-fired my occasional interest in low-power, super-wide-angle binos. If anything comes of that, you’ll hear it here first.

So, all in all a fantastic observing session, with some of the best views of Jupiter and Saturn that I’ve ever had. I should do this more often.

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Observing report: InSight Delta V launch from Vandenberg

May 5, 2018

The InSight Delta V rising above the western horizon as seen from Claremont. Composite of three raw iPhone 7 shots.

This morning at 4:05 AM PDT, a United Launch Alliance Delta V rocket blasted off from Vandenberg Air Force Base, carrying the InSight lander to Mars. For the first time ever for a Vandenberg launch, London and I got up to see it. We went to the top of the 1st Street parking garage in downtown Claremont.

I’d only ever seen one rocket launch before, another Vandenberg launch back in 2010. But I was at the All-Arizona Star Party for that one, so all I saw was a little red spark cruising along the western horizon. Not bad for being 400 miles away, but it didn’t give me a sense of what to expect from here, where we’re still 170 miles out as the crow flies.

The InSight Delta V passing Jupiter as seen from Claremont. Composite of five raw iPhone 7 shots. Trajectory line added in GIMP.

I needn’t have worried – it was extremely cool. The rocket exhaust was easily visible to the naked eye, rivaling Jupiter in brightness. London said he could see the plume of fire as an extended object. His eyes are noticeably sharper than mine and I don’t doubt it. I couldn’t make that out with my own eyes, but it was dead easy in binoculars, and even my phone captured the exhaust plume as a little inverted teardrop of fire. I assembled these composites of the rocket lifting above the western horizon and then flying past Jupiter just a few minutes later, right before main engine cut-off. We saw a brief flare as the second stage lit, but it’s a much smaller engine and it rapidly disappeared from view.

I have to thank PVAA newsletter coordinator Claire Stover for putting me onto the Launch Alert mailing list, which sends updates about upcoming launches. There’s a Falcon 9 set to lift off from Vandenberg in a couple of weeks, on May 19. I think that will be a daylight launch, so I don’t know what to expect in terms of visibility. I’ll keep you posted.