Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Asteroids On-line Lesson On-line Lesson: Asteroids What are they? • Asteroids are solid pieces of rock that have been left around the Solar System from the time when the planets formed. • They range in size from one metre ( or perhaps smaller ) up to 1000 km. • Asteroids are quite irregular in shape and therefore the light they reflect from the Sun fluctuates as they move and rotate. On-line Lesson: Asteroids What do they look like ? • We have never seen any asteroids close up but in a telescope they look like a tiny point of light. • Unlike comets, they have no cloud of diffuse light around them. • Because they are very cold they don’t emit much radiation themselves but they can be seen by very sensitive Infra-Red telescopes such as ISO. On-line Lesson: Asteroids • Asteroids are very irregular in shape as these pictures taken from a spacecraft nearby show. • They are quite similar to small planets or moons like Phobos On-line Lesson: Asteroids How Many Are There? • Recent surveys using Infra-Red telescopes indicates that in the main Asteroid belt around the Sun there are at least 1.1 million asteroids larger than 1 km. On-line Lesson: Asteroids Different types By studying both the brightness and the reflectivity of certain colours it becomes clear that asteroids fall into several different groups. M are believed to be metallic C are thought to be carbonaecous S contain more silicates On-line Lesson: Asteroids Where are they? • Asteroids circle around the Sun in orbits that trace their origins in the Solar System. • The orbits of asteroids are more or less circular and they have orbital periods of three to six years. • Not all orbits around the Sun are populated with asteroids because the motion of the main planets interferes with some orbits and makes them unstable for asteroids. • The majority of asteroids are in the Asteroid Belt with distances from the Sun between 2.2 and 3.2 astronomical units. On-line Lesson: Asteroids Detection • Looking for asteroids in a telescope requires a search for objects which move from one night to the next and are point like in appearance. • To be sure that it is an asteroid rather than a planet or comet, enough observations must be taken to be able to measure the mathematical parameters of the orbit. On-line Lesson: Asteroids Are Asteroids Safe? • Asteroids pass through the Solar System in their orbits, which can change with time as they are affected by passing planets. • If an asteroid was deflected from its orbit onto a path that intersected that of the Earth, the results would be very serious. • An object 100km across hitting the Earth at 20 km/sec would could immense damage. On-line Lesson: Asteroids Have they hit us before ? Many scientists believe that asteroids have hit the Earth many times in its history. Artists impression of a giant asteroid impact On-line Lesson: Asteroids • Because the effect of such a collision would be so dramatic, the signs of this can be seen in the geological record sometimes as huge craters. • An event of this kind may have caused the atmospheric and climatic disturbance which led to the destruction of the dinosaurs.