SCIENCE

Discovering asteroids: what they are and how "planets" are formed

30 June was World Asteroid Day, established in 2014 by Unesco to draw attention to the importance of asteroids, also known as minor planets.

The initial idea to establish this day came from a pool of very important and diverse people, such as Brian May, astrophysicist and guitarist of Queen, Russell Louis 'Rusty' Schweickart, Apollo 9 astronaut, Danica Remy, president of the B612 Foundation dedicated to protecting the Earth from asteroid impacts, and Grig Richters, filmmaker and political activist. 

The date of 30 June was not chosen at random, but recalls the events of Tunguska, which took place in 1908. So what are asteroids, and how did they form in space and around our planet?

Di NASA/JPL - NASA planetary photojournalhttp://photojournal.jpl.nasa.gov/catalog/?IDNumber=PIA00069
World Asteroid Day
30 June was World Asteroid Day, established in 2014 by Unesco to draw attention to the importance of asteroids, also known as minor planets.
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The initiative
The initial idea to establish this day came from a pool of very important and diverse individuals, such as Brian May, astrophysicist and guitarist of Queen, Russell Louis 'Rusty' Schweickart, Apollo 9 astronaut, Danica Remy, president of the B612 Foundation dedicated to protecting the Earth from asteroid impacts, and Grig Richters, filmmaker and political activist.
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Why the date of June 30 was chosen
In Tunguska, a remote region of Siberia in Russia, an asteroid or comet explosion due to friction with the earth's atmosphere, some 5-8 kilometres above the surface, occurred in 1908, according to the most widely accepted hypothesis to date. The explosion demolished tens of millions of plants over an area of 2150 square kilometres of Siberian taiga. It was the most violent impact of a cosmic object in the Earth's atmosphere recorded so far in the history of mankind.
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What are asteroids
According to the definition of the Inaf (National Institute of Astrophysics), asteroids are rocky bodies ranging in size from a few hundred metres to even 900 kilometres. They are also called 'small planets' due to their small size. They have a shape that is usually irregular, and there are different types. The composition of asteroids is very heterogeneous: some asteroids consist mainly of metals, others of rock while still others contain frozen water and carbon compounds.
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The first asteroid
The first asteroid ever discovered by man was sighted in 1801, by the Italian astronomer Vincenzo Piazzi, who decided to name it 'Cenere'. Since then about a few thousand have been discovered and named, but most are still unknown because they are too small.
Di NASA - Cropped from TIFF image from [http://www.solarviews.com/cap/ast/gaspra3.htm Solarviews.com
Where the asteroids are found
Most asteroids are concentrated in the empty belt between the orbits of Mars and Jupiter. They revolve around the Sun in the same direction as the planets, and take three to six years to complete their revolution. It is thanks to the gravitational attraction of Jupiter, which tends to 'hold' the small planets towards itself, that the asteroids do not fall towards the inner planets, driven by the Sun's gravitational attraction.
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How asteroids were formed
The origin of their formation still remains a mystery, or rather, nothing is certain, but it is likely to be the remains of a missed planet that should have formed between Mars and Jupiter. The fact remains that their 'birth' occurred at the same time as that of comets and planets.
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