Smaller Space Rocks Sneak In and Blow Up
    By Enrico Uva | February 16th 2013 05:26 AM | 2 comments | Print | E-mail | Track Comments
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    When I first heard about the blast in Russia, I was unaware that an airbursting asteroid is called a bolide. Explosive events resulting from smaller bodies are far more likely than doomsday-style collisions. But they could do their fair share of damage; yesterday, I was surely not alone in being reminded of the 1908 Tunguska event in Russia.  
    According to this two year-old article, Forget Big Asteroids: It's the Smaller Rocks That Sneak In and Blow Up, bolides form in the Earth's atmosphere every two to twelve years. They are caused by an increase in pressure in front of a moving meteor. That compression is what causes both the increase in heat and shock wave. Proportional to the density of the medium and to the square of the velocity of the moving body, ram pressurecan also dramatically affect entire galaxies.

    Likely, I'm also not alone in forgetting that in late 2009, a bolide exploded over an island in Indonesia, releasing the equivalent in energy of about 100 000 tons of TNT. The responsible asteroid was about 5 to 10 meters in diameter and exploded in the air between 15 and 20 km above the island. A much smaller event occurred in the early 1990s on the south shore of the St. Lawrence River, across from Montreal.* I was a few kilometres from it, but the shock wave caused an earthquake-like tremor that shook my bungalow.

    As Alor, a planetary defense expert, pointed out a couple of years ago, you don't see bolides in time to do anything about it.
    * I can't find any reports about it on the web. I do recall that it was associated with a meteor, but the tremor may not have resulted from a bolide but from an actual impact on the ground. A more recent event in Nova Scotia with reports of a " mysterious boom" was more likely to be from ram pressure.


    I didn't realize bolides were restricted to bursts, I thought they included the flash gordon style flaming balls crossing the sky.

    Referring to the never wrong Wikipedia "One definition describes a bolide as as a fireball reaching an apparent magnitude of −14 or brighter."
    Never is a long time.
    I thought they included the flash gordon style flaming balls crossing the sky.

    could be...I'm not the authority on bolides. In fact I just learned how to spell the word. Until I fixed it, I consistently had a double "l" throughout the blog.