Chelyabinsk: What, Exactly, Just Happened? (Updated)

When you have the largest land mass on Earth, you’re an all-too-likely target.

This morning, Russia was hit once again by a space object, as a bolide exploded over Chelyabinsk, just east of the Ural Mountains, in western Siberia. Eastern Siberia is the site of the largest known strike in modern times, a little over a century ago. It hit in Tunguska in 1908, an air burst with the force of a nuclear weapon, leveling trees for miles around but fortunately injuring or killing few in the sparsely populated region. Had it instead hit in today’s (or even that day’s) New York City, the blast would have killed and injured millions.

And much larger events are possible. To the degree that such a thing can exist, there is now a scientific consensus that the dinosaurs (who didn’t have a space program) were wiped out by a large strike in the Yucatan sixty-five million years ago, clearing the way for placental mammals, who did eventually develop a space program.

Fortunately, today’s event was much smaller -- an explosion high in the atmosphere as entry heating first melted and then boiled the ice inside the frozen rock from deep space, turning it to steam, which blasted the extraterrestrial intruder to pieces. But it happened in a populated area, and the shock wave shattered windows in buildings, injuring over a thousand people at last report. It’s interesting to note in observing the extraordinary video coming from Russia (partially a consequence of so many drivers having dashcams to protect against rampant police corruption) how accurate the special-effects folks in Hollywood have been.

Given that there is a close flyby of another object today, missing the Earth by only a whisker in astronomical terms (just a few earth radii away, and inside the orbit of our communications satellites), it seems like a strange coincidence in terms of timing. When I heard the news of the Russian strike this morning, my most immediate thought was that it was a fellow traveler.

Objects like this are often the result of a breakup of a larger one earlier in the solar system’s history, perhaps due to a collision. Over the eons, the orbits of the ancient debris slowly drift apart from initial differences in their velocity, and from slight differences in infinitesimal forces of solar radiation and wind, and from outgassing, creating a little armada of rocks or ice in loose formation.

The most spectacular example of such a fleet striking a planet was almost two decades ago, when the Hubble Space Telescope watched the debris from the comet Shoemaker-Levy 9 bombard Jupiter, the biggest target in the solar system outside of our star itself, over a period of almost a week. (By remarkable coincidence, it occurred from July 16 through July 22 in 1994, exactly a quarter of a century after the first Apollo lunar landing, whose mission occurred almost exactly over those same dates in 1969, with a return on the 24th.)

So the latest Russian event prompts us to ask if 2012 DA14, the object that has been predicted to fly by for a while (its name indicates that it was discovered last year), is just the largest of a swarm of much smaller ones, previously undetected as this one was, that may continue to hit us for days, like aftershocks of an earthquake.

Initial reports indicated that it was just a coincidence. ESA has claimed that it was unrelated, and NASA scientist Don Yeomans points out that it had a much different trajectory:

Yeomans stressed that the bolide event was likely not associated at all with the incoming asteroid 2012 DA14, which will fly within 17,200 miles (27,000 kilometers) of Earth when it passes safely by our planet today.

“The asteroid will travel south to north,” Yeomans said. “The bolide trail was not south to north and the separation in time between the fireball and 2012 DA14 close approach is significant.”

But some (including me) think that the jury is still out:

The different flyby directions at perigee don’t tell us much. … For departure trajectories we can sketch an entire family of outgoing hyperbolae with asymptotes parallel to the desired departure vector, but with completely different earth-centered inclinations. See the attached scan from Wiesel (1989) but imagine the arrows pointing the other way, to see how two asteroids with slightly different ecliptic inclinations could wind up with radically different (perhaps even 180 degrees different) Earth-centered inclinations at perigee.

I’m not claiming the two objects are related, just saying we can’t rule it out until the trajectory of this new object is traced back to find the asymptote of its approach hyperbola and compare it to 2012DA14.