As if we didn’t have enough to worry about on Earth we also have the constant threat of things in space that could destroy us.
Though there is evidence that vast basaltic volcanism contributed to the downfall of the dinosaurs as much as the asteroid impact, a massive asteroid hitting Earth would certainly ruin most people’s days. The object that created the Chicxulub Crater about 65 million years ago was 170-300km across. This contributed (or was the main cause) of the K-PG extinction event, when all non-avian dinosaurs as well as some three-quarters of plant and animal species on Earth were made extinct. Luckily, NASA has the NEO (Near-Earth Object) programme, which uses a variety of resources to hunt and identify Near-Earth Objects. If any such large asteroid were to make a close-call, we would hopefully know about it in plenty of time.
Though many comets in our solar system have had their trajectories mapped there is still the chance that a collision or a gravitational tug could send an asteroid or a comet on its way to the Sun in a much more elliptical orbit. This could send the comet on a trajectory with Earth. Fortunately, the Near-Earth-Object program listed above also keeps its eye on wayward comets. Jupiter’s strong gravity also acts as a gravity well, sucking rogues and other objects towards it and away from the terrestrial planets.
A gamma ray burst
Recent research suggests a nearby gamma ray burst may have been responsible an intense blast of high-energy radiation that hit the Earth in the 8th century. The evidence comes from the detection of high levels of the isotope Carbon-14 and Beryllium-10 in tree rings formed in 775 CE, which suggest a burst of radiation struck the Earth in the year 774 or 775. the researchers suggested that two stellar remnants (black holes, neutron stars or white dwarfs) collided and merged. Energy is released from such a collision in the form of a burst of gamma rays that typically last less than two seconds. The gamma ray burst was about 3,000 to 12,000 light-years away.
Though a gamma ray burst sounds dramatic, our medieval ancestors may not have noticed much difference. A gamma ray burst at that distance means the radiation was absorbed by our atmosphere, only leaving a trace in the isotopes that eventually found their way into our trees and the ice. Though gamma ray bursts are rare, if another explosion happened at the same distance as the 8th Century event, it could knock out our satellites. If such an event occurred even closer, then it would destroy our ozone layer, with devastating effects for life on Earth.
In 1859, the ‘Carrington event’ was a massive solar flare that sent a cloud of charged particles that struck Earth. This created massive currents in the Earth’s magnetic field and send aurora borealis as far south as