Every year, millions of rocky fragments from outer space burn up in the Earth’s atmosphere, many of them flaring up briefly and appearing in the sky as “shooting stars”. But how many survive their highspeed jumps to hit the ground?
Rocks from space that land on Earth are known as meteorites. Giant impactsas the one that probably ended the reign of dinosaurs About 66 million years ago, caused by an asteroid or comet about 6 miles (10 kilometers) in diameter, they are extraordinarily rare. Instead, most falling rocks land they are very small, and relatively few survive their fiery fall through the Earth’s atmosphere.
Scientists estimate that fewer than 10,000 meteorites hit Earth’s land or water, which is a drop in the bucket compared to the moonthat has no atmosphere and is done impacted by different sizes of space rocks: 11 to 1,100 tons (10 to 1,000 metric tons)—the mass of about 5.5 cars—of space rock dust per day and about 33,000 collisions of pingballsized space rocks pong each year, Live Science previously reported.
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Space rocks that usually end up as meteorites are known as meteoroids—small asteroids, or the smallest members of the solar system. These vary in size from rocks measuring about 3 feet (1 meter) across to micrometeoroids the size of dust grains, according to the American Meteor Society (opens in a new tab)(AMS).
Meteoroids are generally fragments of asteroids or comets. However, some may be debris ejected from planets or moons. For example, there are more than 300 known meteorites that originated as fragments March, according to the Meteoritical Society (opens in a new tab).
As meteoroids pass through Earth’s atmosphere, they burn up due to air friction and produce streaks of light in the sky: these flaming falling rocks are called meteors. A very bright meteor is known as a fireball, according to the AMS (opens in a new tab). Thousands of fireballs flash across Earth’s sky every day, but most of them pass over oceans and uninhabited regions, and many are masked by daylight, the AMS noted.
Most meteors detected on Earth “come from meteor showers associated with dust released by comets,” said Gonzalo Tancredi, an astronomer at the University of the Republic in Montevideo, Uruguay. However, meteor showers do not produce meteorites, as meteorites in such showers are usually too fragile to survive the fall to Earth, Tancredi told Live Science in an email.
To estimate how many meteorites successfully hit Earth each year, Tancredi analyzed data from the Meteoritical Society. From 2007 to 2018, there were 95 reports of meteorites falling on Earth, averaging about 7.9 reports per year.
It is impossible to know for sure how many meteorites fall into the ocean and sink to the bottom undetected. However, 29% of the Earth’s surface is covered by land. Urban areas, where about 55% of the population lives, cover about 0.44% of the land, Tancredi noted.
Tancredi estimated that the total number of terrestrial meteorite falls on Earth was roughly equal to the number of meteorites reported in urban areas divided by the percentage of Earth’s land covered by urban sprawl. In all, he estimated that there are probably “about 6,100 meteor falls a year across the Earth, and about 1,800 on land,” Tancredi said.
Tancredi noted that space rocks about 10m wide are expected to enter the Earth’s atmosphere every six to ten years. A rock large enough to generate an explosion like the one in the 1908 Tunguska event in Russia occurs about every 500 years, he added. A major cosmic impact of a rock about 3,280 feet (1 km) wide is estimated to occur every 300,000 to 500,000 years, while a collision like the one that ended the cretaceous He said that dinosaurs could occur once every 100 million to 200 million years.
Originally published in Live Science.