Making sense of cosmic coincidences

Albert Einstein once said that “God does not play dice with the world.” Many people were inclined to challenge that judgment this month when two extraterrestrial objects intruded on our daily lives, one sideswiping the planet, the other impacting in Russia.

While the first visitor passed a “mere” 27,000 km from Earth, the latter was the largest space rock to hit our planet since 1908. Or so we think. Earth is peppered with space debris daily and while most of it is too small to notice, larger chunks might be making their way to Earth’s surface, but in areas so remote no one ever notices.

Scientists have been watching asteroid 2012 DA14 for about a year since it was discovered by Spanish astronomers at the Observatorio Astronomico de La Sagra in February 2012. Forty-five meters in diameter and weighing 143,000 tons, it is in an Earth-like orbit, circling the sun every 366 days. A year ago it passed 2.6 million km from Earth, but since its orbit is more elliptical than that of Earth, the distance changes.

This year, 2012 DA14 passed a little over 27,000 km from Earth, a distance that is equivalent to twice the diameter of Earth, which makes it seem far away, but within the orbit of geosynchronous satellites, which makes it feel close.

This close to Earth, Earth’s gravity will alter the asteroid’s own orbit; we cannot know the new shape but scientists are not concerned. Its next pass-by will occur in 2046, and it is only expected to come within 1.6 million km from Earth.

For all the attention, DA14 was only the eighth-closest approach by a known asteroid on record. Two years ago, 2011 CQ1 passed within 5,500 km, a distance less than the Earth’s radius. It was only a meter in size, so it is unlikely to have done much damage even if it had hit.

But while astronomers were watching DA14 — and reminding us that an object this size only comes this close to Earth every 40 years on average — a 15 to 17 meters across meteoroid (what scientists call an asteroid before it enters Earth’s atmosphere) crossed the sky over Russia on Feb. 15 in a spectacular display before striking the ground near the city of Chelyabinsk. That impact was the end of a journey that lasted billions of years, and crossed billions of kilometers.

The rock was originally reckoned to have been just 10 tons in size, but subsequent analysis revealed that the estimate was off by a considerable amount. In fact, it likely weighed about 10,000 tons, and produced an explosion equivalent to 50 kilotons of energy, about 20-30 times size of the atomic bombs detonated over Hiroshima and Nagasaki. The blast was strong enough to be detected by 17 nuclear monitoring stations around the world set up as part of the Comprehensive Test Ban Treaty. Over 1,200 people were injured and some 4,000 buildings were damaged. While the total cost of the damage was in the tens of millions of dollars, fortunately no one was badly hurt.

Scientists believe the rock was the largest to have entered Earth’s atmosphere since the Tunguska impact on June 30, 1908, near Podkamennaya Tunguska River in today’s Krasnoyarsk Krai in Siberia. Then, an object thought to have been twice the size of this month’s meteoroid, exploded 5 to10 km above Earth’s surface, knocking down an estimated 80 million trees over an area covering 2,150 sq. km, and producing a shock wave that reached 5.0 on the Richter scale.

These two events have raised fears — or really just reminded us — of the chance of an impact with an object that could threaten our planet, a prospect that has for the most part been relegated to the realm of bad Hollywood filmmaking.

It is estimated that anywhere from 1,000 tons to more than 10,000 tons of material from outer space enters Earth’s atmosphere or lands on Earth every day. Most of it is tiny grit that burns up in the atmosphere without a trace.

Larger objects do penetrate to Earth’s surface, but land in remote places where they vanish without notice. Only about six to eight times a year does an object large enough to leave a sign do so where it can be seen by ordinary people.

NASA, the U.S. space agency, tracks some 10,000 objects in its Near Earth Object program. That sounds like a lot but if objects the size of the Russian meteoroid are included, the number of objects to watch could reach 100 million, many of which are just too small to be tracked with existing technology.

The question is what would humans — as a planet — do if faced with the prospect of a collision with a large object, one big enough to kill cities (like DA14 or even larger).

Conceptually, this idea is called Planetary Defense, and it is exactly what it sounds like. NASA first landed a rocket on an asteroid in 2001 and then launched a projectile into a comet in 2005. The European Space Agency has proposed an Asteroid Impact and Deflection Assessment mission to begin testing Planetary Defense concepts and deflection strategies.

The mission is aimed at intercepting an asteroid three times the size of DA14 in 2022 when it is 11 million km from Earth.

The most important question is whether the odds of success would be sufficient to stave off the panic that would be triggered by reports of the impending catastrophe.

Scientists would argue that the odds of a successful intercept are better than those of such an incident in the first place. That is unlikely to provide much comfort.