Our Solar System was formed 4.568 billion years ago out of a huge cloud of gas, mostly hydrogen and helium, and a small proportion of "dust". Most of the hydrogen and helium has been used to form the Sun, but it's that small amount of dust that has made the difference for all life on Earth! Why? Because the rocky planets of our Solar System - our Earth is just one of them - are made of that dust which is a mixture of iron, oxygen, hydrogen, carbon, nitrogen and many other elements. Not just the Earth itself, but also all life on Earth is made of exactly that same material that astronomers simply call "dust".

Since Pluto lost its planet status we are left with eight planets. The four innermost planets Mercury, Venus, Earth and Mars are terrestrial planets; they are mainly composed of rock. Jupiter and Saturn are the two gas giants, mainly composed of Hydrogen and Helium and the two outermost planets Uranus and Neptune are the so-called Ice Giants, primarily composed of frozen water, ammonia and methane. We also have the asteroid belt between Mars and Jupiter with its millions of smaller and bigger asteroids, which is responsible for most of the meteorites that arrive on Earth. Out in Pluto's orbit there is the Kuiper belt, a huge collection of icy bodies, between 20 and 200 times more massive than the asteroid belt. Since Pluto is just one of the many objects in this belt (and not even the biggest) it has lost its planet status.

If we travel still further out we finally reach the final part of the solar system, the Oort cloud. The Oort Cloud consists of trillions of icy objects (and we are just talking about objects with a diameter of > 1 km) that are still gravitationally bound to the Sun. These objects extend to roughly one light year, almost a third of the distance to the closest star to us, Proxima Centauri. Once in a while some of these objects in the Oort Cloud get deflected from their original orbit around the Sun, thus becoming comets with a very long orbital period of tens of thousands to several millions of years. Comet Panstarrs (C/2011 L4), which visited the inner part of the solar system in February and March 2013, was one of these comets. The next time it will visit us will be around the year 108 000.

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Published by Published or last modified on 2015-10-16