Science News: Close Encounter with a Second Sun

Meteor trace over Chelyabinsk, Russia. Source: Nikita Plekhanov via Wikimedia Commons Related Links Meteorites from Mars 2013 Year in Review 2013 Science News

First the terminology. Asteroids are billions-years-old leftovers from unsuccessful attempts to make planets. They are asteroids while they orbit the sun. When they enter Earth’s atmosphere, however, they become meteors. And when the meteors fall to earth, they are meteorites.

Space Invasion?

On Feb. 15, 2013, a space rock more than 55 ft in diameter and weighing 10,000 tons entered the Earth’s atmosphere at more than 40,000 mph. It broke apart 12-15 mi from Earth’s surface with an explosion of more than 470 kilotons of energy. To put this into perspective, the earliest atomic bombs generated about 15-20 kilotons of energy.

For people in the Russian city of Chelyabinsk, this meant the appearance of a “second sun,“ which produced enough heat to cause instant sunburns and temporary sun-blindness and a shockwave that shattered windows, damaged buildings, and generated a deafening bang. More than 1,500 were injured.

Getting to Know the Meteorite

On Oct. 16, 2013, the meteorite fragment fished from the Lake Chebarkul, southwest of Chelyabinsk, weighed in at over 1,250 lbs before breaking apart-literally tipping and then breaking the scale used to weigh it, according to a local news agency. Although the meteorite’s “landing“ had been easy to locate due to a 20-foot hole in the ice, scientists had to wait until the ice melted before they could liberate the space rock. During the seven-month wait, they used sonar analysis to pinpoint its location, at a depth of about 40 ft and covered by 8 ft of silt.

As the analysis of the lake-liberated meteorite begins, we already know more about this particular meteor than any other that came to Earth before, thanks to both amateur and professional technology. And what we are continuing to learn troubles some. Piecing together footage from vehicle dash-cams and security cameras, as well as data gleaned from infrasound sensors monitored by the Comprehensive Nuclear Test-Ban-Treaty Organization (CTBTO), scientists now think these events aren’t as rare or as benign as previously believed.

Until Chelyabinsk, NASA’s threshold for concern had been space rocks at least 100 ft wide. Some scientists attribute the significant physical ramifications of this meteor’s atmospheric entry and impact to the narrow angle of entry. Regardless, the Chelyabinsk meteorite is now tangible proof of what can and will happen, researchers now say, with greater frequency. In a study published in the journal Nature, scientists tentatively name the asteroid that gave birth to the Chelyabinsk meteor: a 1.25m-wide rock called asteroid 86039. Based on research identifying other such asteroids in orbit, scientists had posited that such an event would occur once every 150 years. But recent studies indicate an outlook of every 30 years at best. Now astronomers, scientists, and certainly people on the ground, are looking up more often, wondering when the next one will come.