ASTEROIDS are rocky bodies left over from the formation of the Solar System. They are often called “minor planets”. The word “asteroid” means “star-like” in greek, because asteroids look like tiny shiny stars when we look at them through telescopes. They are irregularly shaped and vary in sizes from 1km to 1000 km. The three largest asteroids are Ceres (975 km), 4 Vesta (500 km) and 2 Pallas (500 km). WHERE Asteroids are concentrated in a few groups and orbit the Sun as part of their group: 1. Most asteroids concentrate in the area between orbits of Mars and Jupiter called Asteroid Belt. The Belt contains 1-2 million asteroids larger than 1 km and millions of smaller ones. Ceres, 4 Vesta and 2 Pallas are part of the Belt. Though there are so many asteroids in the Belt, the total mass of the asteroids is 4% of the mass of the Moon (with Ceres, Vesta and Pallas together making up a half of this mass). Asteroids in the part of the belt closest to the Sun take about 3 years to orbit the Sun, in the furthest from the Sun part they take about 6 years to orbit. 2. Trojans are asteroids that share the orbit with a planet or moon but don’t collide with it because they orbit either ahead or behind their planet or moon. Jupiter shares the orbit with Trojans. Mars has a few Trojans too. 3. Near-Earth Asteroids (NEAs) are asteroids whose orbit is close to the orbit of the Earth. Scientists think there is about a 1000 NEAs larger than 1 km and 13.000 smaller ones. WHAT’S INSIDE There are 3 known types of asteroids (depending on the composition): 1. C-type (carbon reach) 2. M-type (metallic) 3. S-type (silicate) Over 75% asteroids we find are C-type asteroids. More recent classification suggests not 3 but 24 types of asteroids! CAN WE SEE THEM? Only one asteroid called 4 Vesta (the second biggest asteroid in the Asteroid Belt) is bright enough to be seen with the naked eye. If we cannot see them, than how do scientists “hunt” for new asteroids? They use telescopes with photo cameras! The trick is to take images of the same area of the sky during a course of an hour and then compare those images to see if there are any objects on them that changed their position. Everything that moved can be an asteroid! A few asteroids were visited by spacecrafts, for example a probe called NEAR Shoemaker orbited asteroid Eros and then touched down on that asteroid at the end of its mission. Dawn probe has been orbiting Vesta for a year and is now orbiting Ceres (since 2015).
Fun Facts: ● June 30 is an “International Asteroid day”. The goal of this day is to educate people about asteroids and what can be done to protect our planet. ● Some asteroids have moons. ● People plan to mine asteroids in the future.