Further thoughts on fireballs, asteroids and coincidence

Fragments said to be from the Russian meteorite fall ring the hole in Chebarkul Lake. Credit: Reuters: Chelyabinsk region Interior Ministry

Asteroid 2012 DA14 has moved on, and the Russians are busy cleaning up the mess from yesterday’s fireball. Hopefully a few people are also busy looking for meteorites from the fall. The only meteorite-maybes I’ve seen photos of are the small, black rocks found around the perimeter of the hole in Chebarkul Lake, west of Chelybinsk.

A Tagish Lake meteorite fragment. Credit: Michael Holly, Creative Services, University of Alberta.

If these are indeed meteorites from the bolide, they remind me of the black, carbonaceous debris dropped by the Tagish Lake fall over the Tagish Lake area in British Columbia on January 18, 2000. Carbonaceous chondrites are fragile, carbon-rich meteorites that easily shatter into dust and small bits during a fall. If that’s what we’re dealing with here, meteorite hunters better get cracking – this type erodes quickly. Divers found no trace of any meteorites in the lake at the bottom of the hole today.

It is odd though that two days have gone by without a single significant fragment found. Meteorites, which develop a black fusion crust on atmospheric entry, would show up beautifully against the snowy Russian landscape. So what gives? How long will see purported Chelyabinsk “meteorites”pop up on eBay before the real item finally shows? Only hours after the fall, the first dubious specimens appeared on the auction site. Not a one of them looks like a fresh fall and some are clearly not meteorites. Buyer beware!

These MET-7 satellite photos clearly show the Russian fireball traveling from east to west. North is at top. Asteroid DA14′s trajectory was south to north or nearly perpendicular to the fireball’s. Click for more information and a short video. Credit and copyright: EUMETSAT

As for the Russian fireball being related in any way to the asteroid flyby, it is not. I’ve been in touch with folks who orbits and it’s becoming even clearer that we’re dealing with two very different asteroids. Not only were their orbits nearly perpendicular to each other from the perspective of the Earth, but it’s not possible for a cloud of DA14 fragments to even reach the city of Chelyabinsk at 55 degrees north latitude in Russia.

Since the fragments would approach Earth from due south nearly parallel to the planet’s axis, if they hit the planet, they’d strike the southern hemisphere. From the fragments’ very-close-to-Earth perspective, Chelyabinsk, Russia is on the far or opposite side of the globe and totally out of sight. Amateur asteroid discoverer Dr. Marco Langbroek uses this analogy and I paraphrase slightly:

“Compare it with a car. A bird flying toward your car will always hit the front of the car – it cannot hit the back of the car. Chelyabinsk at 55 North latitude is “the back of the car” in this comparison, given the approach direction of 2012 DA 14 and any fragments of it.”

We place a lot of faith in coincidence because, well, if you drop a plate, it breaks. The two are related. So if two close meteors or asteroids appear around the same time, many of us make the assumption they’re related too. It totally makes sense to wonder about a connection between the two events, but once the data is in, we need to take another look at our surmise. Speaking of data, we’re still waiting on radar images from the Goldstone antenna. As soon as they’re available, you’ll see them here.

Animation of DA14 made from images taken this morning from New Mexico. Credit: Ernesto Guido and Nick Howes

I’m curious if any of you got to see the asteroid flyby either through binoculars or telescope. If so, we’d love to hear your story. Clouds were cruel here in Duluth, Minn., but I stood at the telescope and waited. And waited. Finally, a few thin openings passed the asteroid’s location just above the bowl of the Little Dipper about 7:15 p.m. (CST). There was just enough time to identify DA14 and watch it scoot north. One minute of joy followed by hours of clouds.

Cosmic debris rains down through the atmosphere nearly every day, accumulating at a rate of 37,000 to 78,000 tons per year. While that may sound like a lot, much of it is dust or passes unseen over the oceans.

At least a half-dozen times a year, however, a fireball burns up over a populated area and drops meteorites. Their fall is pinpointed by careful analysis of the angle of entry based on eyewitness reports, Doppler weather radar, security cameras or even dashboard cams, as we saw in Russia on Friday. Once the word is out, everyone from those closest to the areas of impact to meteorite hunters from across the planet are eager to find a piece of otherworldly treasure. The Chelyabinsk region has been pretty much off-limits to foreigners until recently, so it should be interesting to see who gets in and out without being arrested.

What they’re looking for are leftover fragments from collisions of bodies in the asteroid belt between Mars and Jupiter. Over the eons, Jupiter’s gravity nudges the shattered rocks out of the belt, sending them toward the inner solar system. Millions of years later, those fragments may hurl toward Earth. As the space rocks plummet through the atmosphere, the heat and pressure become so intense that even a fairly large object, say 13 to 50 feet across, will more often than not burst into harmless pieces that fall to the ground as meteorites.


The famous Peekskill fireball of October 9, 1992 that dropped a meteorite that smashed the rear end of a Chevy Malibu

A 13-footer hits our planet about once a year. One the size of Friday’s fall in Russia — about 50 feet across and weighing about 7,000 tons — strikes Earth about once every 50-60 years. The bigger they are, the less frequently they fall but the greater the consequences.

Yesterday’s flyby asteroid 2012 DA14, a rock about 150 feet across, would have caused regional devastation had it struck in one piece. One that size only rings our bell every thousand years. An asteroid of about 0.9 miles across could cause planet-wide devastation and climate change. The good news is such an event happens only once in half a million years.

While most of the 0.9-mile and larger near-Earth asteroids have been discovered, there are something like a million others as big as the one that zoomed by harmlessly yesterday. Sky surveys have ferreted out many of them, but many more remain to be found — before they find us. While there are many great ideas about how we might deflect an asteroid headed toward Earth, there are presently no programs underway to accomplish that goal.

34 thoughts on “Further thoughts on fireballs, asteroids and coincidence

  1. The best comment I’ve heard on the Russian meteorite: It’s nature’s way of asking, “How’s that space program going?”

  2. Thanx for the article, you know I was wondering about if there was a relation between DA14 and Chelyabinsk.

    About my personal story about checking DA14…

    It was a clear night. Here in Italy one could see the asteroid at close approach at around mag 8. But exactly in those hours I had to play jazz…

    After the musical evening, though I was tired and DA14 was far at mag 13 (nearly the 13.8 visual limit of my C8 scope), I decided for desperation to go with the scope on highland, to have reasonably low light pollution. It was indeed dark, also windy, there was snow around and I was alone, not the happiest conditions. If a werewolf came out I wouldn’t have been too surprised.

    I setup the scope and was well equipped with the coordinates of DA14 at each half hour, which I had downloaded at home by Heavens-above.com. I couldn’t see the asteroid in visual. But then I tried in photocamera, with few seconds of exposition at high sensibility. I soon took another shot, compared it with the previous one, and noticed clearly an object which had moved significantly respect the stars. You would have heard a person in the night in country shouting “Yesss!”.

    I got about 20 photos to make a rough movie (I will share it in a few days). Now knowing exactly where to look I tried to see it visually but I got the confirm that it was too weak. I did all just in time, in few minutes the first light of the dawn came.

    So glad that I didn’t lose it. It was a very special personal moment.

    Looking forward to your stories!

  3. Hi Bob,

    Awesome meteor event. But you said the Russian meteor was 7000 tons. I thought reports were saying it was 10 tons. Has that been adjusted? I calculated a 10 ton object traveling at 10 miles per second as having 280 kiloton of TNT for energy.

    On another note, seeing was great last night. I watched a shadow transit, I think Io’s, on Jupiter, the Orion Nebula looked beautiful, and the moon was so crisp.

    Jim

      • Bob,
        Here’s a little math for those of us who are not real sure what something this size should weigh, and would like to know which number is in the correct ballpark.

        If we assume the meteor was a sphere 50ft across (which most accounts agree on), the volume of that sphere would be 65,450 cubic feet (based on 4/3*pi*r^3). Using the weight of 7000 tons, it would weigh 1,400,000 pounds, giving us a density of 213.9 pounds per cubic foot (pcf). Using the weight of 10 tons, it would weigh 20,000 pounds giving us a density of 0.306pcf.

        For comparison, steel weighs about 495 pcf. Limestone and granite are closer to 170pcf, while ice is 57pcf. It seems to me that your number (7000 tons) is correct! (unless my math is wrong)

      • Would a meteor made of high iron/nickel (or most other metals) have burned up and exploded like this one? I think I read somewhere (maybe here on your blog?) that this meteor was made of mostly carbon, which burns pretty good!

        • Bob,
          Much of a meteoroid’s original mass burns up in the atmosphere but stony ones are more liable to disintegrate into small pieces/dust compared to irons. As for explosions, they can happen with both iron and stony meteorites. The Russian event now appears to have been a fairly common type of chondrite (stony) meteorite with little carbon. In my “53 tiny meteorites” blog yesterday, you’ll see photos of pieces.

  4. Hi Bob!
    I was hoping you could shed some light to a comment my friend in California made. He says he seen the Russian meteor from his home in California. Is that possible? Can you please give a quick explanation of how it isn’t or how it could be.Thanks

    • Hi Hesher,
      That’s a great many thousands of miles away, so no, it wouldn’t be possible because the curvature of the Earth would get in the way. However it’s very likely your friend saw another unrelated fireball.

      • One of the dashcam videos I saw was from just less than 800 km away, and the meteor was very low to the horizon at that distance. In fact, if I remember right, the meteor was right at or just below the horizon when it exploded. I’ll see if I can find that video again and post the link.

          • Bob,
            770km — that’s right near the limit for the Russian fireball which burned up between 18 and 30 miles above the ground. At 18 miles – assuming clear air and approx. sea level altitude – it would have been visible at the start of its fiery flight from a distance of 488 miles. At 18 miles, the limit would be 378 miles. Here’s the calculator if you’d like to play around with it:
            http://www.ringbell.co.uk/info/hdist.htm

          • Well, those numbers would seem to match pretty good, Bob. In the video, the horizon is very flat and the fireball explosion is right at the horizon and disappears behind it. Cool!

          • I got thinking a little more about these numbers. If the fireball was 18 miles above the surface, then according to the calculator you linked to, the maximum distance at which it would have been visible would be 608 km. That’s a fair bit less than the reported 770 km in this video. So I got thinking about the variables that might be involved here:
            A) there is the variable of the actual altitude of the explosion: the meteor was descending (rather quickly!) while it was exploding and you referenced that already by pointing out that the explosion was between 18 and 30 miles in altitude.
            B) there is the variable of the measured distance of 770 km: that is, I assume, a rounded off measured distance /by road/, which would include hills and valleys and corners. It would almost certainly not follow the calculated straight line measurement of 608 km.
            C) and maybe, over that much distance, there might even need to be some allowance for the curvature of the Earth, although I don’t know how much difference that might make between the ‘line of sight’ points and the towns on the surface of the Earth.

            Interesting stuff….

  5. http://www.youtube.com/watch?v=odKjwrjIM-k&feature=player_embedded
    I found this video to be interesting because of the time signature. It is almost exactly 90 seconds (+/- 1 second?) from the bright flash of the explosion (seemingly almost immediately overhead of this video) until the first pressure wave (concussion) hits the ground. When I was a kid, we would count the seconds from a flash of lightening until we heard the thunder and we estimated that to be how many miles away the lightening was. I do not know how accurate that is, but if it is even close, then this explosion occurred something like 90 miles above the ground. But I seem to recall reading somewhere that this explosion was only 12 km above the ground which, from the pictures of the smoke trail, seems rather more accurate to me. Can that 90 second delay be used to calculate with some precision just how high that explosion really was?

      • Yes, I suppose it would include any horizontal distance. But from this video, and others taken in Chelyabinsk (I hope I spelled that right), the horizontal distance would have been pretty minimal, I think. It looks like it went almost vertically right overhead; maybe off by 10 degrees or so from vertical? I’m just guessing from the videos, I certainly don’t know that for a fact.

        • Bob,
          For the nearby, overhead fireball pass, I’ve heard it was somewhere in the 28-30 second range for the shock to arrive. From some places however, you can hear multiple explosions that continued for some seconds.

        • ok, so I did a little digging. Sound travels in air at about 768 mph, with some variance for moisture content, temperature, and air pressure. We were way out as kids in our time-to-distance estimates: 5 seconds of delay equals about 1 mile of distance. So using that, 90 seconds of delay for the meteor’s pressure wave would equal about 18 miles of distance. That sounds much more plausible!
          http://en.wikipedia.org/wiki/Speed_of_sound

Leave a Reply

Your email address will not be published. Required fields are marked *

*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>