Today, on June 30, World Asteroid Day is celebrated. The day is an annual global event held on the anniversary of the Siberian Tunguska event that took place on June 30, 1908, the most damaging asteroid-related event on Earth in recent history. The United Nations has declared it globally on 30 June every year in its resolution.
Asteroids are rocks that revolve around the sun like a planet, but are much smaller than planets in size. In our solar system most of the asteroids are found in the asteroid belt in the orbit of Mars and Jupiter. It also roam in the orbital of other planets and along with the planet, it also revolve around the sun. When our solar system was formed about 4.5 billion years ago, then such clouds of gas and dust which could not take the shape of a planet and were left behind, were transformed into these rocks i.e. asteroids. This is the reason that their shape is not as round as that of the planets. No two asteroids are the same. Although you must have heard many times that an asteroid as big as Everest is going to pass near the Earth, then an asteroid of football size is going to come. There are many asteroids in the universe whose diameters are hundreds of miles and mostly equal to a small stone.
Only its size is not important for destruction on Earth. Rather, if a high speed rock is expected to come closer than 46 lakh miles from the earth, then space organizations consider it dangerous. NASA's Sentry system already monitors such threats. According to this system, the asteroid which really threatens the earth is still 850 years away.