Asteroids are rocky celestial bodies that revolve around the Sun, just like planets. Most of the asteroids in our solar system are located in the main asteroid belt, the region between the orbits of Mars and Jupiter. These asteroids are remnants from the formation of the solar system around 4.6 billion years ago. While most of them do not pose a threat to Earth, they can cause catastrophe in case of an impact on the planet. To raise awareness about the asteroid impact hazards, International Asteroid Day is observed on June 30.Here’s everything you need to know about asteroids and why they could pose a threat to the Earth.HistoryJune 30 was designated as the International Asteroid Day by the United Nations to observe the anniversary of the Tunguska asteroid’s impact over Siberia. The devastating event took place on June 30, 1908, in Siberia, and is known as the largest asteroid impact Earth had witnessed in recorded history.According to NASA, “The only entry of a large meteoroid into Earth’s atmosphere in modern history with firsthand accounts was the Tunguska event of 1908.” The United Nations General Assembly adopted a resolution in December 2016 and declared June 30 as the International Asteroid Day.What are asteroids?Asteroids are irregular rocky bodies that revolve around the sun but are much smaller than planets, according to NASA. They are airless celestial bodies that are remnants left over from the early formation of our solar system.Our solar system is packed with these rocky bodies, most of which are located in the main asteroid belt between the orbits of Mars and Jupiter. Many asteroids whizz past our planet safely, but some can get quite close to the Earth’s orbit.These are termed as Near-Earth objects (NEO) and can pose catastrophic threats to the planet. NASA closely monitors these NEOs and according to its Center for NEO studies, there are more than 16,000 Near Earth asteroids discovered.How is International Asteroid Day celebrated?International Asteroid Day is aimed at sensitising people on the dangers of an asteroid impact and familiarising them with the crisis communication actions that must be taken in such an event. Hence, various organisations hold events to educate people on asteroids and the risks they pose.You can view NASA’s special event held to commemorate last year’s International Asteroid Day, where the space agency and experts shared knowledge about asteroids and answered queries related to the interstellar bodies.