A medium-sized asteroid that can crush a city like New York hits the Earth less often than previously thought, once every thousand years rather than about a hundred. This is according to a study that used military satellites
In the photo: remains from the explosion of an asteroid with a diameter of 50 meters in Tunguska, Siberia, 1908
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Rocky space debris created by collisions in the asteroid belt between Mars and Jupiter, or chunks of rock separated from a passing comet, hit the Earth every day as meteorites, but most of the pieces from asteroids or comets are smaller than a grain of rice and burn up quickly in the upper atmosphere as meteors.
Still, in 1908, a meteor up to 50 meters in diameter nearly hit the ground before burning up over Russia, causing an explosion that flattened hundreds of square kilometers of woodland in Tunguska, Siberia. The explosion was about 10 megatons of TNT - or 10 million tons. For comparison, the atomic bomb that was dropped on Hiroshima in World War II exploded with a force of 13 kilotons or 13 thousand tons.
In a new study that examined data produced by military satellites over the past eight years, it appears that medium-sized asteroids like the one that hit Siberia only hit on average once every thousand years and not every hundred or two hundred years as previously thought, says Peter Brown, an astrophysicist from the University of Western Ontario.
The study, published last Thursday in the journal Nature, is based on measurements of the flashes of light created when the fragments burn up in the atmosphere.
Fragments larger than a meter in diameter are also too small to be detected by ground-based camera networks or telescopes, so Brown and his fellow researchers, including General Simon "Pat" Worden of the US Air Force Headquarters, turned to military satellites to use them to detect the lights of nuclear explosions.
By measuring the density of the light flashes using highly sensitive instruments, the researchers were able to estimate the size of the asteroid and the intensity of its explosion.
They were able to detect 300 meteor flares produced by fragments 1994 to 2002 meters in diameter from February XNUMX to the end of September XNUMX. These explosions are no more than one ton of TNT in force, leading Brown to conclude that the chances of a Tunguska-style asteroid hitting Earth again are low. from what they thought before.
Scientists who did not participate in the study were also impressed by the analysis. "It's an interesting approach to studying the phenomenon," says Timothy Spar of the Harvard-Smithsonian Center for Astrophysics, which participates in studies of near-Earth asteroids. "I'm sure the military has other things to do and it's really good to see that the data can also be used for other uses by the way," Spar said.
Brown also compared his results to telescope data on larger asteroids taken as part of the Near-Earth Asteroid Research Project in New Mexico, operated by Lincoln Laboratories at MIT. "When you draw a line from our data to theirs, they match, which is a surprise because we used completely different techniques and so we're confident that the numbers on both sides make sense.
However, other researchers say that Brown's estimate may be subject to change, such as a comet approaching the Earth and raining fragments of different sizes on the Earth. The study estimates that the flux of asteroids and comets we have observed so far in the last 20-30 years will remain as it is, a basic assumption accepted by some astronomers with skepticism," says Benny Pizer, an anthropologist at John Moores University in Liverpool, England, who led the international forum about The asteroid threat Pfizer says the study should reassure the public that scientists are developing better ways to prepare to the asteroid threat, and this will lead to ways to prevent, or at least reduce, the risk. Pfizer says the research is valuable in a different direction, because it helps show that the U.S. military can tell the difference between atomic explosions and meteors and refers to both - a capability that may give the government protection against classification. Mistaking a meteor crash for an atomic weapon explosion, with all that implies.
For information on the Nature website
They knew cosmic collisions
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