Meteor Showers!

The 2012 Geminids over South Dakota. Image credit: David Kingham.

Meteor showers are some of the most beautiful sights one can see with their naked eye, and they have the marked advantage of appearing at almost the same time every year! Very young, we’ve learned to call these luminous streaks across our sky shooting stars, but they are not stars at all, but rather flaming space debrsi! Every year, around 15,000 tonnes of these debris, from sand grain sized to boulder sized, enter the Earth’s atmosphere. As they burn up, they leave behind brightly visible paths. While few meteors survive their journey and fall to the ground as meteorites, most are completely destroyed before impact. 

A few times a year, these shooting stars happen in swarms, sometimes inundating our skies at a rate of up to thousands of meteors per hour! In such impressive cases, they are called meteor storms rather than simple showers. But why do we witness sudden surges of shooting stars at the same time every single year? The answer is comets! We all know about comets: icy bodies orbiting around our Sun, periodically appearing in our skies as bright tailed objects. The trajectory of some of these comets crosses the trajectory of Earth’s orbit. Obviously, the comets and Earth do not cross this point at the same time or that would mean bad news for us! However, comets do leave behind long-lasting trails of debris into which Earth passes once a year, like clockwork. Some of these particles crash through our atmosphere and delight us in the form of a meteor shower. The intensity of each meteor shower depends on the density of the particle cloud leftover by the comet, the position of other planets in our Solar System, the intensity of the Sun’s activity and many more complex variables. Luckily, there are over 50 meteor showers every year, many of which are visible to the naked eye so there’s always a chance to spot a shooting star. The two most prominent showers are the Perseids in mid-August and the upcoming Leonids in mid-November!

Meteors over Russia

A video of the meteor zipping through the air above Chelyabisnk, Russia. Video credit: Wikimedia Commons/Aleksandr Ivanov.

Small rocks enter the Earth’s atmosphere every single day. These are typically the size of a pebble and burn up quite harmlessly many tens of kilometers up into our atmosphere. At larger intervals of time, however, Earth is assaulted by much larger asteroids. On February 15th of this year at 9:20am local time, an asteroid estimated to weigh 11,000 tonnes entered the atmosphere over Chelyabinsk, Russia and subsequently exploded at a height of about 24 km, releasing the equivalent energy of 30 times that of the Hiroshima atomic bomb. The shockwaves that followed the bright explosion damaged upwards of 7,000 buildings and injured about 1,500 people. Now that everyone is only ever a few feet away from some sort of camera, the impressive event was extremely well documented. It is not, however, the first known event of its kind.

The Chelyabinsk meteor is the largest known object to have entered Earth’s atmosphere since what is known as the 1908 Tunguska Event. Meteor airbursts of this size occur every 100 years or so. The Tunguska Event luckily happened over a barren region in Siberia, where only very few eyewitnesses were reported to have seen a great flash of light and feeling a powerful shockwave that knocked them off their feet. The explosion may have been over 30 times more energetic than the Chelyabinsk meteor airburst. It registered on seismographs as an earthquake of 5.0 on the Richter scale and set the nightskies of Europe and Asia aglow for many nights. We can only theorise what may have happened had such an event occurred over a densely populated region, but the effects would most likely have been quite devastating. Later expeditions to the explosion site found entire forests of trees covering an area of 2,150 square kilometers completely scorched and knocked down from the blast.

Due to the remote location of this event, as well as the primitive state of our understanding of meteor behaviour at the time, a number of alternate theories have been proposed to explain the Tunguska Event. These range from a miniature black hole passing through the Earth to a giant pocket of natural gas being released from the Earth’s crust to Serbian inventor Nikola Tesla’s death ray experiment having gone awry. The meteor airburst theory remains the most scientifically supported one to date.

While these events are quite rare, it should be noted that the Chelyabinsk object was completely undetected before it exploded in our atmosphere. Perhaps the Universe is reminding us that we should keep a closer eye on it…