Asteroids and Meteors and Craters, Oh My!

The heavens were full of shooting stars and asteroids this weekend. Is the apocalypse nigh, or is it all just a freaky coincidence? Let’s take a look at the incidents.

Asteroid 2012 DA14 was discovered on February 23, 2012. Within weeks, astronomers knew that it would pass very close to Earth on February 13, 2013, but that we weren’t in any danger of a collision. In the weeks leading up to last Friday’s flyby, we were reassured that the asteroid had been tracked very closely and that while there was a minute chance it could collide with a communications or navigational satellite, it would still be about 17,200 miles above the surface of Earth at its closest approach. That’s why it was such a shock to see a fireball in the skies over Russia on Friday morning.

At about 9:25 a.m. local time, the meteor crossed the sky above the Chelyabinsk region of Russia. As it burned up in the upper atmosphere, it was briefly brighter than the sun. The shock wave, which can be heard in the video below (turn down your speakers!), was powerful enough to set off car alarms and shatter windows; estimates of the number of people injured by flying glass range from 700 to more than 1,000.

The meteor is estimated to have been 15 meters (about 50 feet) in diameter, with a weight of 7000 metric tonnes (7700 tons). We didn’t know it was coming because of its small size; there’s an array of telescopes that search for potentially dangerous asteroids, but their search is focused on objects from 100 meters to a kilometer in size. Still, it’s likely the largest object to strike the Earth (albeit in fragments) since the Tunguska Event in 1908, in which a low-altitude atmospheric explosion caused damage over an estimated 2,150 square kilometres (830 square miles) in Siberia. Since the meteor broke up into smaller pieces before impact, there’s no single large crater. A hole measuring 10 meters (33 feet) across was found in the ice covering Chebarkul lake, with smaller fragments being found on top of the snow across the region. There have been reports that the meteor left a burning crater in its wake, but they’re hoaxes – the footage is actually of the Darvaza gas crater in Turkmenistan, which has been on fire since 1971.

So is the Russian meteor in any way related to the passing of Asteroid 2012 DA14? Nope, not at all. Phil Plait explained why not on the Bad Astronomy blog.

For one thing, this occurred about 16 hours before DA14 passes. At 8 kilometers per second that’s nearly half a million kilometers away from DA14. That puts it on a totally different orbit.

For another, from the lighting, time of day, and videos showing the rising Sun, it looks like this was moving mostly east-to-west. I may be off, but that’s how it looks. DA14 is approaching Earth from the south, so any fragment of that rock would also appear to move south-to-north.

Footage of the meteor’s trail taken by a Russian weather satellite confirmed that it had passed from northeast to southwest, so the timing was just a really freaky coincidence. In fact, DA14 passed by exactly as expected and without any damage to Earth.

Shooting stars were also reported this weekend over San Francisco, Cuba, and Florida. Further coincidences that were only widely reported on because of their proximity to the other events? Probably so. Shooting stars can be seen year-round, and while their numbers are highest during the meteor showers of August and November, February tends to have an abnormally high number of bright fireballs in the sky. Scientists haven’t yet figured out the cause of the increase.

In an even stranger coincidence, Australian scientists just announced the discovery in the outback of the third-largest impact crater ever found. The impact zone measures more than 200 kilometers (125 miles) across and has been hidden until now because it’s at a depth of about 4km (2.5mi). Analysis of drill cores found rocks that had been melted into a glass-like material by the heat of the impact. The crater was formed at least 298 million years ago; if further testing pushes this date back, the impact could be a factor in the Devonian extinction that took place 360 million years ago.