Space Collisions: Tunguska, Andromeda and You

What happens when worlds collide? A distant star suddenly burns a little brighter. NASA throws another psychedelic photo gallery up on the Web. Star junkies get in a tizzy. Like a well-meaning dad taking a whiffle bat to the groin, collisions between cosmic bodies are amusing as long as we’re not on the receiving end.
Hitting Way Too Close to Home Fortunately, Earth has only experienced one particularly frightening collision in recent history. In 1908, a 10 to 15 megaton explosion shook central Siberia, felling an estimated 80 million trees and racking the region with seismic waves. Potentially 1,000 times more powerful than the atomic bomb that leveled Hiroshima, the Tunguska Event was most likely caused by an asteroid or comet. Luckily, the Tunguska region was sparsely populated, but if the fragment had hit the rotating Earth as little as 4 hours and 47 minutes later, it would have decimated St. Petersburg, then the capital of Russia’s empire.
Experts disagree on the possible size of the Tunguska Event fragment, with estimates varying between tennis court-sized and football field-sized. Now imagine what an object 6 miles (10 kilometers) across could do. That’s the estimate some experts give for the object that caused the K-T boundary extinction event. This impact took place 65 million years ago and likely killed off nearly every large vertebrate species on the planet, including the dinosaurs. Earth’s distant past experienced even greater impacts. Some scientists theorize that the moon is the result of a massive collision between our planet and another cosmic body.
Neighborhood Collisions Earth isn’t the only planet in our solar system to experience jarring collisions. We’ve found Martian rock on Earth, thrown from particularly hellacious impacts on the red planet. Just beyond Neptune’s orbit, fields of floating debris mark the collision point between two massive objects at some point in the planet’s distant past. The resulting explosion would have been the equivalent of 10 billion nuclear bombs going off at once. Such debris is called a collision family, and our solar system is home to at least 35 of them — most of which reside in the asteroid belt between Jupiter and Mars.
Collisions Outside the Solar System If the above cosmic mash-ups sound impressive, imagine what might transpire when stars or entire galaxies crash into one another. According to the Big Bang theory, everything in the cosmos is essentially shrapnel spinning out from the mother of all explosions. Early on in the universe’s history, cosmic collisions were more common, but they still happen. Even our own galaxy, the Milky Way, carries with it debris from ancient galactic mergers. Using space telescopes and computer modeling, astronomers have observed the aftermath of similar mergers, as well as the dance of neutron stars steadily sucking each other into a black hole-birthing collision.
A Fatal Meeting Is there another galaxy out there with our name on it? There sure is. Scientists expect the Andromeda galaxy (currently 2.5 million light years away) to collide with the Milky Way in the far-distant future.
Originally published by Discovery Space.
Robert Lamb is a senior writer and podcaster at HowStuffWorks, where he co-hosts Stuff to Blow Your Mind with Julie Douglas. He has a love for monsters, an aversion to slugs and a hankering for electronic music.
Topics in this Post: Stuff to Blow Your Mind


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