The triggered origin of the solar system

The scenario of the triggered origin of the solar system suggests that the formation of our planetary system was initiated by the impact of an interstellar shock wave on a molecular cloud core. The strength of this scenario lies in its ability to explain the presence of short-lived radionuclides in the early solar system. According to the proposal, the radioactivities were produced in a stellar source, transported into the molecular cloud core by a shock wave and mixed into the collapsing system during the interaction between the shock wave and the core. We examine the viability of the scenario by presenting results from recent numerical simulations. The calculations show that molecular cloud cores can be triggered into collapse by the impact of a shock wave propagating at the velocity of 10–45 km s⁻¹. Some of the shock wave material incident on the core, typically 10–20%, can be injected into the collapsing system. The time scale of the process is ∼10⁴–10⁵ years, sufficiently short for the survival of the short-lived radioactivities. The simulations therefore confirm the viability of the scenario of the triggered origin of the solar system.