The Chelyabinsk Surprise
Copyright © 2013 by Ralph F. Couey
Written content only.
Earth has been visited lately, not by aliens in flying saucers, but rocks of varying sizes the appearance of which has caused quite a stir. That earth gets hit is not really news. Several thousand objects collide with our atmosphere each day, most the size of a grain of sand. A few are larger, perhaps baseball-sized. Once a week on average Earth receives a rock about the size of a house. Most burn up in the atmosphere, the larger ones lighting up the sky. The American Meteor Society website lists reports of fireballs happening virtually every day. Damage from these is non-existent to slight. But lately, it seems that the sky has gotten much busier.
March 22nd, a rock estimated to be 3 feet wide lit up the skies over the eastern U.S., generating sighting reports from 13 states. On the night of March 16th, another fireball created by a rock of as-yet unknown size was seen over North and South Carolina, and Tennessee. While all this was going on, Comet Pan-STARRS was painting its tail across our planet’s skies.
Of course, everyone remembers the bomb over Chelyabinsk, Russia on February 15th. This 45-foot-wide rock exploded before hitting the ground, causing wide-spread damage and inflicting injuries on some 1,500 people. This was the same day that an expected visitor, a 150-footer called DA14, passed just above our atmosphere, below the altitude of our communication satellites. Scientists knew this one was coming, but the Chelyabinsk rock surprised everyone.
In the skies over Earth’s southern half, Pan-STARRS was accompanied by another cosmic snowball, Comet Lemmon. But the real…um…”star” of the show will be Comet ISON, which is expected to become visible in late November, and is predicted to be the brightest comet seen by anyone alive today. That’s exciting news. The last visible comet to fly by was Hale-Bopp 15 years ago. They’re rare events to be sure. To have three visible to humans in one year is amazing.
Earth has been hit by space bodies before, mostly in the early epochs billions of years before life arose. In fact, there’s a lot of agreement that the ingredients for life were brought here by the impact of comets. Use of sophisticated technology has uncovered many craters, most of which were obscured by the effects of weather and continental drift. Some, like Arizona’s Barringer Crater, are obvious. This hole, three-quarters of a mile wide and some 570 feet deep, was dug out by a nickel-iron impactor that was about 160 feet wide with a mass of 150,000 tons. At the time, 50,000 years ago, Arizona was a verdant grassland. But if a similar object were to hit Manhattan, it would result in severe damage out to 50 miles and kill hundreds of thousands.
Arizona's Barringer Crater
Photo by NASA
As scary as that sounds, it gets worse. The rock that is suspected to have killed the dinosaurs, struck near what is now a small Mexican fishing village called Chicxulub 65 million years ago. This 6-mile wide impactor excavated a crater 110 miles across and may have been as much as 1,600 feet deep.
The largest one, however, may be a structure recently discovered under the ice of Eastern Antarctica. The jury is still out on this one, but the crater, if that’s what it is, is 300 miles wide. That rock that produced this structure is estimated to have been 30 miles wide. The last two discussed both produced global disasters and mass extinctions.
The power of such a strike derives from three variables, the size and type of the impactor, and how fast it’s traveling when it hits the ground. The Arizona object generated a force of 10,000 megatons. The Mexican dinosaur killer exploded with a force of 100 million megatons. In case you’re wondering, the calculated global catastrophe threshold is 100,000 megatons.
Artists conception of Asteroid Apophis (1,150 wide, 40 megatons of mass) hitting the Earth, probably a NASA image.
One would think that with all the technology humans possess that impending collisions would be easier to spot. This delusion was put firmly to rest by NASA Chief Charles Bolden in testimony before Congress March 20th. When asked what we could do if an asteroid on an Earth-collision trajectory were detected three weeks before impact, Bolden replied, “Pray.” I found that assessment more than a little disquieting.
It’s not like we don’t have enough to worry about. Iran is a year away from producing a nuclear weapon. North Korea is issuing dire pronouncements. Israel and Syria look to be getting ready to lock horns. Now on top of all that, we have to also worry about death from space?
Actually, it isn’t very productive to worry about things over which we have no control. As tough as things are for the average American right now, we have more than enough on our plate. Earth has been hit before; it’s inevitable that it will happen again, perhaps tomorrow, maybe not for thousands of years. There are a multitude of proposals for dealing with a potential planet killer, but that’s all they are for the moment. Mr. Bolden was right in that we really don’t have anything that we could take off the shelf and throw into space. The default action would be the use of nuclear weapons. But those kind of explosions behave differently in space than they do in an atmosphere. It’s likely that such an attempt would take a Chicxulub-sized rock and turn it into a thousand Barringers. Millions would still die.
Money is tight everywhere. Even the Chinese are no longer flush. Any of the plans out there would require the investment of hundreds of millions for development, testing, construction, and deployment, and multiple tens of millions more for a proper Near Earth Object (NEO) tracking network. No government has that kind of free cash right now, and it’s unlikely that we could afford the cost in the forseeable future.
But how can one rationally say we can't afford to prevent Armageddon?
Our fragile, naked home.
Image from NASA, Apollo 8