“The current standard theory for Solar System formation, the nebular hypothesis, has fallen into and out of favour since its formulation by Emanuel Swedenborg, Immanuel Kant, and Pierre-Simon Laplace in the 18th century.”
Problems With the Outdated Theory:
“The physics of accretion disks encounters some problems. The most important one is how the material, which is accreted by the protostar, loses its angular momentum. One possible explanation suggested by Hannes Alfven was that angular momentum was shed by the solar wind during its T Tauri phase. The momentum is probably transported to the outer parts of the disk, but the precise mechanism of this transport is not well understood. The process or processes responsible for the disappearance of the disks are also poorly known.
*The formation of planetesimals is the biggest unsolved problem in the Nebular Disk Model. How 1 cm sized particles coalesce into 1 km planetesimals is a mystery. This mechanism appears to be the key to the question as to why some stars have planets, while others have nothing around them, even dust belts.
The formation of giant planets is another unsolved problem. Current theories are unable to explain how their cores can form fast enough to accumulate significant amounts of gas from the quickly disappearing protoplanetary disk. The mean lifetime of the disks, which are less than 107 years, appears to be shorter than the time necessary for the core formation.
Another problem of giant planet formation is their migration. Some calculations show that interaction with the disk can cause rapid inward migration, which, if not stopped, results in the planet reaching the “central regions still as a sub-Jovian object.”
“One unresolved issue with this model is that it cannot explain how the initial orbits of the proto-terrestrial planets, which would have needed to be highly eccentric to collide, produced the remarkably stable and near-circular orbits the terrestrial planets possess today”
“The Solar System is chaotic over million- and billion-year timescales, with the orbits of the planets open to long-term variations. One notable example of this chaos is the Neptune-Pluto system, which lies in a 3:2 orbital resonance. Although the resonance itself will remain stable, it becomes impossible to predict the position of Pluto with any degree of accuracy more than 10–20 million years (the Lyapunov time) into the future. Another example is Earth’s axial tilt which, due to friction raised within Earth’s mantle by tidal interactions with the Moon will be incomputable at some point between 1.5 and 4.5 billion years from now.
The outer planets’ orbits are chaotic over longer timescales, with a Lyapunov time in the range of 2–230 million years. In all cases this means that the position of a planet along its orbit ultimately becomes impossible to predict with any certainty (so, for example, the timing of winter and summer become uncertain), but in some cases the orbits themselves may change dramatically.”
“The more new planets we find, the less we seem to know about how planetary systems are born, according to a leading planet hunter.
With the tally of confirmed planets orbiting other stars now more than 500, planet hunters are heading for a golden age of discovery, said Geoffrey Marcy of the University of California, Berkeley.
But that bonanza has been a headache for theoreticians, he said, because many of the newly discovered star systems defy existing models of how planets form.”
“New Finds Will Continue to Boggle Theory
Marcy thinks part of the problem is that theoreticians have paid too much attention to interactions with gas and dust and not enough attention to interactions between planets.”