Asteroids and comets
Asteroids and comets are very interesting objects, being the remnants of the earliest years of the formation of our Solar System, more than four billion years ago.
The word asteroid means "star-like" and these objects appear in the sky as bright, point-like stars. But, unlike stars, asteroids are rocks orbiting our Solar System: they don’t emit light on their own and are visible only because they reflect sunlight.
So far, several hundred thousand asteroids have been discovered and thousands more are discovered each year. Most of them are in the Main Belt, a region between Mars and Jupiter located roughly 2 - 4 AU from the Sun. The sizes of asteroids range from dust particles to significant bodies hundreds of miles in diameter (Ceres, the largest observed is 913 km of diameter). Globally, the total mass of all the asteroids is less than that of the Moon.
Comets are often called "dusty snowballs", objects made of ice, rock and organic compounds that originate from a region beyond the orbits of the outermost planets (called Oort cloud). Gravitational perturbations periodically jar these objects out of this cloud, sending them on orbits that can come close to the Sun. Some, called long-period comets, follow elliptical orbits that bring them far beyond the planets, while others, called short-period comets, travel in shorter orbits nearer the Sun. When comets come in the inner Solar System, the ices in the comet solid part, called nucleus, begin to vaporize and form the characteristic, beautiful tails that sometimes can be seen from Earth.
Scientists think that while striking the early Earth billions of years ago, comets have created major changes to Earth's early oceans, atmosphere and climate, and may have delivered the first carbon-based molecules to our planet, triggering the process of the origins of life.
Why are asteroids and comets important?
The chemical and physical characterization of asteroids and comets is very important, first of all, from a scientific point of view. Since asteroids and comets are leftover of the primordial solar system, studying their composition and their structure will make us know more on the formation of the Solar system. A second good reason to study asteroids and comets comes from the threat that they may represent for us, when coming near our planet and becoming NEOs.
Last update: 9 May 2012