It is interesting to note that more is known about the origin of distant stars than about the origin of our own solar system, which consists of the Sun and the planets, asteroids, comets, etc. that orbit it. This is because the solar system formed long ago, and we have no other examples of young solar systems to observe at close range. A current approach to studying the formation of the solar system is to study the formation of new stars. It is hoped that this data can be used to create a model that explains the formation of solar systems. Scientists are able to train their telescopes on multitudes of large stars in various stages of development; unfortunately, many of these stars are too far away to allow observation of how planets may be forming in association with them.
At one time, it was widely believed that planets in our solar system formed when a star passed close to the Sun, tearing away matter that then condensed into planetary bodies. Subsequent calculations have shown that matter removed in this way would either fall back to the Sun or fly into outer space. Today, most experts favor some variation on the solar nebula theory, which holds that the solar system formed from a cloud of particulate matter called cosmic dust. The details of this theory, however, are widely debated.
Even the details regarding the formation of the Sun, the star in our solar system, are not agreed upon. The Sun may have formed from material remaining from a star that imploded, or collapsed violently, to form heavy elements. After this collapse, a supernova—or an exploding star that casts off matter of low density—was formed. The supernova remnants formed a dense cloud or nebula that then formed the Sun. There is also a possibility that it formed alone from a nebula made of various types of dust and gas not necessarily remaining from a supernova and then captured a cloud of cosmic dust that then formed the planets. Alternatively, the Sun and the planets may have formed from the same dust cloud.
Amidst all of the uncertainties regarding the origin of the solar system, one thing seems certain: The planets formed either during or soon after the birth of the Sun. In fact, the Sun and the planets appear to have originated during a remarkablyshort interval of time possibly no longer than about 100 million years.