Doomsday, Whenever: Massive Asteroid Impacts Probably Happen at Random

We always seem to be “overdue” a devastating asteroid impact, but how can we be overdue if asteroids don’t have an impact schedule?

Don Davis/NASA

Humans are naturally tuned to seek out patterns in seemingly random events. It’s an evolutionary trait that has helped us become the smart Homo sapiens we are today.

This ability to spot patterns and predict cyclical events continues to dominate our everyday lives. For example, geologists chart seismic activity in hopes of seeing a tell-tail earthquake signal before the “big one” happens; farmers track seasonal cycles in an attempt to predict periods of drought; Wall Street traders use complex numerical models to warn of the next financial crisis (or, indeed, profit from the downturn). Also, astronomers try to find patterns in cosmic occurrences that could pose an existential threat.

We are, of course, talking asteroid impacts — cataclysmic events that have shaped all of the planets in our solar system. Although Earth’s atmosphere is very good at eroding away ancient impact craters, evidence for asteroid impacts in the geological history of our planet is very common. Frankly, it’s perfectly natural to be hit by large asteroids and comets; that’s how planets accrete rocky material, collect water and accumulate organic chemistry for life (on Earth, at least).

But should we get hit by a massive asteroid in the near future, it could be curtains for our civilization. So it sure would be handy if we could somehow use the geologic record of our planet, see how often we get punched, spot a cycle or some kind of pattern, predict then the next impact is likely to happen and — hopefully — plan for the next marauding space rock to make an appearance in our skies! (Whether we’ll be able to do anything about it is an entirely different matter.)

Although seeking out cycles in asteroid and comet strikes is a doomsayer’s favorite hobby, scientists have had a challenging time at pinning down any kind of pattern in historic asteroid impacts and, as a new study published in the journal Monthly Notices of the Royal Astronomical Society dramatically concludes, there may be no pattern at all.

But what could drive periodic asteroid or comet impacts in the first place? One hypothesis claims that the solar system’s “wobble” through the galactic plane may destabilize comets in the Oort Cloud periodically, causing an uptick in massive planetary impacts. Also, the much hyped solar twin, Nemesis, could gravitationally jumble asteroids during its long orbit around the sun. But neither hypothesis stands up to scrutiny and the existence of an extremely dim solar partner is becoming increasingly unlikely.

Regardless, previous studies have suggested that extinction-level impacts (of the magnitude of the one that wiped out, or at least greatly contributed to the extinction of the dinosaurs) occur roughly every 26 million years (the cause of which is open to debate), but researchers from ETH Zurich and Lund University in Sweden now refute this claim.

“We have determined … that asteroids don’t hit the Earth at periodic intervals,” Matthias Meier, of ETH Zurich’s Institute of Geochemistry and Petrology, said in a statement.

After studying precisely-dated impact craters around the world that were formed in the past 500 million years, Meier and Sanna Holm-Alwmark of Lund University dated some 22 craters with dates of impacts known to a precision of one percent.

Then, using a technique known as circular spectral analysis (CSA), they attempted to find the approximate-26 million year period in this set of craters. They found no such period.

Interestingly, Meier and Holm-Alwmark also found that some of the impact craters were of the same age, hinting at a common source. “Some of these craters could have been formed by the collision of an asteroid accompanied by a moon,” said Meier. “But in other cases, the impact sites are too far away from each other for this to be the explanation.”

One interesting example is the apparent close similarity in age of the famous 66 million-year-old, 110 mile-wide Chicxulub Crater in Mexico (that has been linked with the extinction of the dinosaurs) and the 15 mile-wide Boltysh Crater in the Ukraine. As pointed out by the researchers, although a definitive explanation for this coincidence isn’t immediately clear, the two impactors may have originated from a collision in the asteroid belt, sending fragments to Earth, hitting the planet within a very short period of one another.

And it’s these kinds of clustering impacts that the researchers have identified as being potential problems with previous statistical studies — they assumed each impact is distinct, when in fact, they happened at the same time, possibly skewing results and creating a pattern when, in fact, there wasn’t one.

“Our work has shown that just a few of these so-called impact clusters are enough to suggest a semblance of periodicity,” said Meier.

I have little doubt that these new findings will be disputed, spawning more studies pointing to other statistical techniques and a bigger impact crater data set, but it is interesting to think that, as far as extinction-level impact events go, there really may be no pattern to their occurrence.

We know that a doomsday asteroid is out there, and it will hit us, but it has a random impact date that is only known to our planet’s geological future.