Formation of solar systems in the universe
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Interstellar Molecular Cloud Collapse and Protoplanetary Disk Formation
The formation of solar systems in the universe begins with the gravitational collapse of a region within a giant interstellar molecular cloud. This collapse is triggered when the cloud's self-gravity overcomes internal pressures, causing it to contract and fragment into denser clumps. The majority of the material falls toward the center, forming a protostar, while the remaining gas and dust flatten into a rotating protoplanetary disk around the new star Marov2018Ford2014Nimmo1986+3 MORE. This process is observed in star-forming regions throughout the galaxy, providing strong evidence for its universality Ford2014Nimmo1986.
Accretion and Planetesimal Formation in Protoplanetary Disks
Within the protoplanetary disk, dust grains collide and stick together, gradually building up larger bodies called planetesimals. These planetesimals, ranging from a few kilometers to hundreds of kilometers in size, serve as the building blocks for planets. Over time, continued collisions and gravitational interactions cause planetesimals to merge, forming protoplanets. Some planetesimals remain as asteroids or comets, preserving a record of early solar system conditions Marov2018Nimmo1986Russell2007.
Simultaneous Star and Planet Formation
Recent advances in theory and observation support the idea that stars and their planetary systems form simultaneously. As the protostar ignites nuclear fusion at its core, the surrounding disk continues to evolve, with regions of instability leading to the rapid formation of protoplanets. This scenario is consistent with the Kant-Laplace hypothesis and is supported by observations of young stars with surrounding disks and ongoing planet formation Marov2018Nimmo1986Pierrehumbert2021+1 MORE.
Role of Star Clusters and Environmental Influences
Many solar systems, including our own, are thought to have formed within star clusters. The density and dynamics of these clusters can influence the properties of emerging planetary systems, such as the number and arrangement of planets. Interactions with nearby stars or supernovae may also affect the evolution of the protoplanetary disk and the final architecture of the system .
Meteorites and the Chronology of Solar System Formation
Meteorites, especially chondrites, provide direct evidence of the early solar system. Isotopic dating of these materials reveals that the solar system formed about 4.56 billion years ago. The composition and structure of meteorites help reconstruct the sequence of events, from dust grain condensation to planetesimal and planet formation, and even major impacts that shaped planetary bodies Nimmo1986Russell2007.
Outstanding Questions and Theoretical Models
While the general sequence of solar system formation is well established, several questions remain. These include the details of angular momentum distribution, the reason for planets orbiting in a single plane, and the differences in evolutionary paths among neighboring planets like Earth, Venus, and Mars. Various models, including those considering the contraction of the protosun and the influence of random motions in the original cloud, attempt to address these issues Marov2018Avagyan2018Smith2021.
Conclusion
The formation of solar systems is a complex, multi-stage process that begins with the collapse of interstellar clouds and proceeds through disk formation, planetesimal accretion, and planetary assembly. Observations of young stars, meteorite analysis, and theoretical models all contribute to our understanding, though some mysteries remain. The process appears to be common throughout the universe, making planetary systems a natural outcome of star formation Marov2018Ford2014Nimmo1986+4 MORE.
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New Model on the Formation of the Solar System
The Solar System formed from a single stream of dust and gas, providing answers to the paradoxes of angular momentum, planets being on a single plane, and Protoplanets originating after each contraction of the Protosun, in order of their distance from the Sun.
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