According to officials with NASA and the US Geologic Survey (USGS) the meteorite that flashed across the sky over Chelyabinsk, Russia Friday morning is not only the biggest meteor the Earth has directly encountered in over 100 years, but the shockwave from when it exploded shook the ground like an earthquake.
The last time something like this happened was nearly 105 years ago, in June of 1908, when a 40 m object (either a meteor or a comet) exploded over the Tunguska region of eastern Russia. The shockwave from that event leveled trees over 2,000 square kilometres and apparently registered as a magnitude 5.0 earthquake to seismic instruments across Eurasia.
Scientists are still working on the exact details, but the object that exploded over Chelyabinsk was a bolide — a meteor that explodes into extremely bright fireball. Estimates put it at roughly 17 meters long, with a mass of about 10,000 metric tons. It entered the atmosphere travelling at 15-20 km/s (54,000-72,000 km/h), leaving a vapour trail hundreds of kilometres long and exploding somewhere between 30-50 kilometres above the ground, with a force equal to a 500 kt nuclear bomb.
The shockwave from the explosion took between one-and-a-half to two-and-a-half minutes to reach the ground, and when it did, it shattered thousands of windows in communities around the region, as well as causing several building fronts to buckle from the stress and it apparently collapsed the roof of a zinc factory. To seismographs around the world, it registered as the equivalent of a magnitude 2.7 earthquake.
Last reported, over 1,100 people were injured, either by flying broken glass or meteorite fragments, and nearly 3,000 buildings — including 34 healthcare institutions and 361 schools — were damaged. Last count, the damage estimate was 1 billion rubles, equal to more than 33 million dollars.
Initially classified as just a meteor, the object was then called a meteorite when evidence was discovered of fragments reaching the ground. One particularly large fragment (possibly the main surviving chunk of the meteor) smashed through the ice covering Lake Chebarkul, about 80 km west of Chelyabinsk.
The difference in terminology for meteors, meteoroids and meteorites may seem subtle, but it is significant. The term meteoroid is used for anything floating around in the solar system that's anywhere from the size of a grain of sand up to as big as a boulder. The visible streak in the sky created when a meteoroid encounters the atmosphere is called a meteor. A meteoroid that survives creating a meteor trail and impacts on the ground is then called a meteorite.
There has been some question about whether or not this asteroid was connected with asteroid 2012 DA14, which made an extremely close pass by the Earth on Friday afternoon. However, whereas some asteroids and meteoroids flying around in space aren't alone as they do so, these two encounters were entirely coincidental. There's a very cool graphic at The Telegraph that illustrates it.
The reason that astronomers can be so certain of this is due to the trajectories of the two objects. The meteor that streaked across the sky above Chelyabinsk today traveled from northeast to southwest. Asteroid 2012 DA14 swung by the Earth traveling from south to north. If the two objects were somehow related, their paths would have been more parallel to each other.
Another question being asked is why, if we knew asteroid 2012 DA14's path so exactly, and we know the positions and paths of other objects out in space so well, how did this meteor over Russia catch us off-guard?
The sad truth is that we have no idea exactly how many meteoroids and asteroids there are flying around out in space, and the smaller an object is, the harder it is to see it. With this object over Russia only being 17 metres wide, it is extremely difficult to see objects of that size unless they are made of an extremely reflective material, and rocks floating around in space are notorious for being made of dark materials.
[ More Geekquinox: Russian meteor causes sonic booms, rains down debris ]
As I learned from Phil Plait (@badastronomer) today, there are two satellite missions in the works to help with this problem though.
One is the Sentinel Mission, being developed by the B612 Foundation. This satellite will orbit around the Sun at roughly the same distance as the planet Venus scanning out towards Earth's orbit with infrared instruments to spy asteroids and meteoroids.
This will complement the NASA WISE mission (Wide-field Infrared Survey Explorer), which has been in operation since 2009, and has already provided data that suggests there are between 3,200 and 6,200 potentially-hazardous asteroids (PHAs) whizzing around out there.
One thing seems clear from the events of the past day, though. The issue of near-Earth asteroids and their danger to us is not something we can ignore. We can only hope that the U.S. Congress can follow through on their plans to schedule a hearing on the issue of potentially-hazardous asteroids, and that this hearing will actually see some real results — like increased funding to NASA, and to organizations like the B612 Foundation, so that we can better protect ourselves in the future.
(Images courtesy: Getty/US Geologic Survey/Andrey Orlov, Chebarkul/EUMETSAT/NASA JPL)
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