Amazingly, thousands of rocks from space hit the surface of Earth each day. Every year our planet puts on nearly 10,000 tonnes in weight due to meteoroids entering the atmosphere. Many of these are minuscule grains of dust, but some can be many metres in length. The world’s largest known meteorite was discovered in Namibia, Africa, in 1920. It weighs an incredible 55,000 kg (120, 000Ibs).
To date, there have been nearly 1,100 recovered falls (meteorites seen to fall) and nearly 40,000 finds (found, but not seen to fall). It is estimated that probably 500 meteorites reach the surface of the Earth each year, but less than 10 are recovered. This is because most fall into the ocean, land in remote areas of the Earth, land in places that are not easily accessible, or are just not seen to fall (fall during the day). From a model animation, it appears that lots of small asteroids/large meteoroids pass close to the Earth each day. Most of these are not detected, but recently, three 5–10 meter “asteroids” have been discovered and have passed well within the orbit of the Moon. Also recently, an asteroid about 500 meters in diameter passed about 2 million km from the Earth (five times the distance to the Moon). It is estimated that each day one or two 5–10 meter objects pass within the Moon’s orbit and that there are probably 30 million near-Earth objects! Most of these are too small to ever cause any damage. Five to ten meters is probably the smallest object that would likely survive passage through the Earth’s atmosphere.
While large impacts are fairly rare, thousands of tiny pieces of spaces of space rock, called meteorites, hit the ground each year. However, the majority of these events are unpredictable and go unnoticed, as they land in vast swathes of uninhabited forest or in the open waters of the ocean, Bill Cooke and Althea Moorhead of NASA’s Meteoroid Environments Office told Space.com.
In order to understand meteorite impacts on Earth, it is important to know where the chunks of rock come from. Meteoroids are rocky remnants of a comet or asteroid that travel in outer space, but when these objects enter Earth’s atmosphere, they are considered meteors. Most (between 90 and 95 percent) of these meteors completely burn up in the atmosphere, resulting in a bright streak that can be seen across the night sky, Moorhead said. However, when meteors survive their high-speed plunge toward Earth and drop to the ground, they are called meteorites.
The Perseid meteor shower — one of the most popular meteor showers of the year — is expected to put on a particularly breathtaking show Aug. 11 and 12, when the Earth passes through the trail of debris created by Comet Swift-Tuttle. However, viewers should not expect to find any meteorites lying on the ground after this spectacular meteor shower. “Perseids come from Comet Swift-Tuttle and are very fragile, being an ice-dust mix,” Cooke said. “They are not strong enough to survive passage through the atmosphere at 132,000 mph (212,433 km/h) and so never produce meteorites — they are totally vaporized by the time they make it to 50 miles (80 km) altitude.”
Picture Credit : Google