Feeling secure beneath burning space-rocks in the sky

Ever since learning about the Chicxulub asteroid event that wiped out most of the dinosaurs, my kids have been greatly concerned at any mention of red-hot rock falling out of the sky. This is, of course, understandable, since an object 110 miles across hitting the Earth would, once again, be catastrophic to life as we know it. However, smaller versions of this happen all the time, it seems valuable to try and appreciate the difference between a rock that practically remade the planet, and a rock the size of a sofa over Arizona. As proven by the occurrence last week, the latter happens from time to time, and assuming it doesn’t distract someone while driving a car, leaves us no worse for wear.

Early morning event

On June 2, the early-morning sky over Arizona was lit up as a glowing meteor, or bolide, burned and broke apart in the atmosphere. For a bit of panache, it was punctuated by a few flashes of light as larger bits of rock broke apart, releasing a larger pockets of energy at once. For those that missed the bright but brief pyrotechnics, a trail of vaporized rock remained airborne long enough to be stirred and twisted by the wind. Importantly, no injuries or damages were reported, and there probably wasn’t even enough material falling from the sky to leave any meteorites on the ground.

The Jet Propulsion Laboratory (JPL) was able to put together a few details on this particular rock, mainly because it was so well reported. Based on the amount of energy released (around half a kiloton of TNT,) and the speed of 12 miles per second, it seems that this was likely a couch-sized object that weighed around 10 tons when it entered Earth’s atmosphere. At this point scientists have also been able to calculate the meteor’s trajectory, but that shouldn’t suggest that this particular stone-sofa bears any special significance to the state of the world, or even Arizona.

More meteors, or more reporting?

As you can see from the JPL webpage documenting meteors witnessed on Earth, even an incomplete record of these objects adds up pretty quickly. While most incoming rocks probably end up over the ocean, as humans have more and more ways to track and record such events, we’ll probably hear more about them in the coming years. Citizens of St. Louis were treated to a bolide this morning, in fact, and like the 10-ton rock from Arizona, it seems to have been nothing more than a spectacle. Their may be bits of burning rock up there, but there’s no reason to start worrying that the sky is falling.

My first grader asked: Could this meteor have been made by the [Kuiper belt] objects Planet 9 disturbed? Did they bang into each other and chip a piece off?

Since a trajectory was calculated, it looks like this particular rock was in an orbit that only occasionally went as far as Mars from the Sun. Prehaps it was once a piece of something from the asteroid belt between Mars and Jupiter, but it seems that it may have been in an orbit in Earth’s neighborhood for some time, finally running into us last Thursday.

Source: Fireball: Couch-Sized Rock Lights Up the Sky Over Arizona by Phil Plait, Bad Astronomy