عنوان مقاله [English]
نویسنده [English]چکیده [English]
The Solar System is exposed to collision with rocks that have remained since the formation of the planets. Asteroids and meteorites are examples of this group of rocks.
The first known asteroid was discovered by the Italian astronomer Giusepppe Piazzi on January 1, 1801, and was called “Ceres” after the goddess of plants in ancient Rome. This asteroid is located at an average distance from the Sun of less than 2.8 AU (Astronomical Unit) (2.8 times the distance of the Earth to the Sun) and it takes it 4.6 years to traverse its orbit around the sun. The largest asteroid has a diameter of about 1000 km. Its mass is supposed to be about 30% of the total mass of all asteroids. Three asteroids of Ceres, Vesta and Pallas have a diameter of 500 km, and it is estimated that there are at least 100,000 asteroids with a diameter of about one kilometer, but there are more than 200 asteroids whose diameter is about 1000 km.
It was once thought that asteroids are the pieces produced by the “efforts” of a former planet. But if we bring all asteroids together in a single unit, this unit will equal about 5% of the mass of the Moon, and this amount of matter can only form a body with a width of 1500 kilometers. Most astronomers now believe that asteroids are objects that whose formation goes back to the time of formation of planets, namely 4,500 million years ago. These pieces could never come together to create a single planet.