Seventy per cent of Earth's surface is covered by water, meaning if we were unfortunate enough to be struck by an enormous asteroid, it'd probably make a big splash. A team of data scientists at Los Alamos National Laboratory recently decided to model what would happen if an asteroid struck the sea. Despite the apocalyptic subject matter, the results are quite beautiful.
Image: Los Alamos National Laboratory
Galen Gisler and his colleagues at LANL are using supercomputers to visualise how the kinetic energy of a fast-moving space rock would be transferred to the ocean on impact. The results, which Gisler presented at the American Geophysical Union meeting this week, may come as a surprise to those who grew up on disaster movies like Deep Impact. Asteroids are point sources, and it turns out waves generated by point sources diminish rapidly, rather than growing more ferocious as they cover hundreds of kilometres to swallow cities.
The bigger concern, in most asteroid-on-ocean situations, is water vapour.
"The most significant effect of an impact into the ocean is the injection of water vapour into the stratosphere, with possible climate effects," Gisler said. Indeed, Gisler's simulations show that large (250m-across) rock coming in very hot could vaporise up to 250 metric megatonnes of water. Lofted into the troposphere, that water vapour would rain out fairly quickly. But water vapour that makes it all the way up to the stratosphere can stay there for a while. And because it's a potent greenhouse gas, this could have a major effect on our climate.
Of course, not all asteroids make it to the surface at all. Smaller sized ones, which are much more common in our solar neighbourhood, tend to explode while they're still in the sky, creating a pressure wave that propagates outwards in all directions. Gisler's models show that when these "airburst" asteroids strike over the ocean, they produce less stratospheric water vapour, and smaller waves. "The airburst considerably mitigates the effect on the water," he said.
Overall, Gisler says, asteroids over the ocean pose less of a danger to humans than asteroids over the land. There's one big exception, however, and that's asteroids that strike near a coastline.
"An impact or an airburst [near] a populated shore will be very dangerous," Gisler said. In that case, the gigantic, city-devouring tsunami every B-list disaster movie has primed you for might actually arrive.