Free Astronomy Magazine March-April 2018

SOLAR SYSTEM 23 W e know a lot about the evolution of the Solar System from its birth to today. Some processes we un- derstand in detail, others are only broad outlines, but all in all, we have a suffi- ciently clear framework. Conversely, we know very little about the mechanism that triggered the formation of the Sun and all the bodies that orbit around it. The pre- dominant hypothesis has it that an inter- star at the Solar System T he Bubble Neb- ula (NGC 7635) is about 8000 light years from Earth and originated from the brilliant Wolf-Rayet star visible to the left of its centre. [NASA, ESA, Hub- ble Heritage Team] MARCH-APRIL 2018 stellar cloud of dust and gas was hit by the shock wave from a supernova, with conse- quent compression of the material. The higher density regions therefore began to attract other matter gravitationally until reaching concentrations and temperature levels sufficient to trigger thermonuclear reactions. Thus a cluster of stars was born, one of which was the Sun. Then, the dif- ferent proper motions of individual stars