Exoplanets and Exoplanetary Systems: Pasts and Futures

Abstract

There are still some uncertainties over the details of how planets, brown dwarfs and stars come into being. The basic process however is clear – a diffuse cloud of gas and dust in inter-stellar space whose mass can range from one to ten million solar masses and whose diameter can range from a light year to hundreds of light years collapses under its own gravitational pull and ends up as one, a few, hundreds or thousands of smaller objects whose masses range from a tiny fraction to a 100 or so times that of the Sun. The smaller objects have densities ranging from a tenth to ten times that of water – a factor of some 100,000,000,000,000,000,000 (10²⁰) or so times denser than the original inter-stellar cloud.