In an amazing coincidence, two large space rocks came within close proximity of the Earth within the same day.
An asteroid was already being tracked by astrophysicists around the world, with its trajectory expected to pass through the ring of artificial satellites that orbit the Earth. However, a totally unexpected meteorite seemingly came out of nowhere—its advent hidden by the Sun’s morning rays—and exploded about 10,000 metres (about 6 miles) in the atmosphere above Chelyabinsk, home to about 1.2 million people in central Russia.
The sonic boom that shook the area resulted from a bolide, which is what scientists call a meteor when it turns into a fireball. A meteor entering the Earth’s atmosphere will burn from the friction of passing through the atmosphere. Often the meteor transitions to the meteorite stage as it breaks into small pieces that hit the ground with relatively little damage. This one, however, exploded once and then three more times.
Before it reached the atmosphere, scientists estimate that it was about 17 metres (55 feet) in diameter. Earlier approximations put it at about 15 metres, but its size was revised upward as a result of tracking information available from an infrasound station in Alaska and analysed by scientists at the University of Western Ontario in Canada. At the time of the explosion, it was about 10,000 metres above Earth, travelling at a rate of 20 kilometres (12 miles) per second. Its passage across the plane of the Sun shows that it was travelling north to south.
It was almost 9:30 a.m. in the Urals Mountain region when the explosion occurred. People out and about beginning a normal weekday heard the sonic boom, felt a shockwave, and saw windows shattered in buildings all around them from the boom. Car alarms were jolted into action and mobile phone networks were interrupted. Additional damage to the buildings came from the meteorite, but most of the 1,000 people who sought medical treatment for injuries were cut from flying glass. About 50 of them required some hospitalisation; there were no fatalities.
It has been 115 years since an object came that close to the planet, and that event also occurred over Russia. In 1908 a meteorite exploded over the Podkamennaya Tunguska River in Siberia. Astrophysicists refer to these kinds of events as impacts, even though the meteorite breaks up before it actually hits the Earth. Scientists had far inferior equipment at that time, and the explosion occurred in an isolated area, but it is believed the explosion took place between 5 to 10 kilometres (3-6 miles) above Earth. That meteorite was estimated to be 100 metres wide, and it levelled 80 million trees in a 2,150 square kilometre (830 square mile) area. To put that in perspective, the pyroclastic blast of the Mount Saint Helens volcano in the United States in 1980 levelled trees in an area of 600 square kilometres (230 square miles).
In the second astral event of the day, a huge asteroid passed uncomfortably close to the planet—but scientists felt confident it wouldn’t hit Earth. They had been tracking the asteroid named DA14 since February 2012, and they were setting up observation posts beginning at 9 a.m. in the eastern United States and about 5:00 p.m. in Italy at the Virtual Telescope Project. Scientists fully expected for the asteroid named DA14 to travel from south to north against the afternoon sky on February 15; they’d been tracking it since February 2012.
Scientists insist there is no correlation between the two astral bodies passing so close to Earth on the same day. The trajectories, with the Chelyabinsk meteorite coming from the north and the asteroid coming from the south, were entirely different.
The closest that DA14 came to Earth was 27,700 kilometres (17,200 miles). The satellites that it passed through were about 5,000 kilometres farther out, maintaining a geosynchronous orbit, which means their orbit takes place within the 24-hour time span of the Earth’s rotation. DA14’s diameter is estimated to be approximately 45 metres (150 feet) across. This astral body is much denser than the meteorite that exploded above Chelyabinsk, another reason why scientists know that the two are unconnected. The next time its orbit comes close to Earth will be 2046.
A meteoroid is a space rock that’s no larger than a metre (3.3 feet). It’s usually made of cosmic dust that has broken off of a bigger cosmic body made of rock or metal called an asteroid. A meteorite is a piece of a meteor or meteoroid that actually manages to make it through the atmosphere and strike Earth. A bolide is an asteroid or meteor that has exploded into a fireball. Current research includes the study of solar electric propulsions that could possibly deflect future astral bodies that come near Earth.
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