A new view on planet formation

Abstract

Abstract. The standard picture of planet formation posits that giant gas planets are over-grown rocky planets massive enough to attract enormous gas atmospheres. It has been shown recently that the opposite point of view is physically plausible: the rocky terrestrial planets are former giant planet embryos dried of their gas "to the bone" by the influences of the parent star. Here we provide a brief overview of this "Tidal Downsizing" hypothesis in the context of the Solar System structure.

Dust grain growth and settling in initial gaseous giant protoplanets

“…Thus, the segregation timescale obtained by the study is quite realistic and also in good agreement with other recently published results with more rigorous treatment of the problem having different numerical codes (e.g. Boss, 1998a;Nayakshin, 2010).…”

“…The sedimentation time as calculated by the model shown in Table 1 in all cases is found to be well within the initial contraction time ∼10 5 years (e.g. Donnison and Williams, 1974;Boss, 1998b;Nayakshin, 2010). Besides r 0 , M and R, the segregation time is also dependent on the parameters λ, µ and η.…”

“…In our study, the three very important effects on grain sedimentation time namely, convection motion acting on the grain, turbulent mixing, and destructive collisions discussed in the investigation of and Nayakshin (2010) have not been included. Moreover, in our calculation the effect of radiative heating and the contraction of the gas near the centre due to the increased pressure have not been considered.…”

“…The basic idea of the model has been pioneered by Kuiper (1951), Urey (1966) and Cameron (1978). With the difficulties encountered with the core accretion models, this type of model, once in vogue and then quickly forgotten, has been revived and reformulated by several authors (e.g., Boss, 1997Boss, , 1998aBoley et al, 2010;Nayakshin, 2010;Cha and Nayakshin, 2011). But some investigations (e.g., Pickett et al, 2000;Cai et al, 2006a, b;Boley et al, 2007a, b) criticized the hypothesis and generally showed that disk instabilities are unable to lead to the formation of self-gravitating dense clumps that could form gas giant protoplanets, whereas Mayer et al (2002Mayer et al ( , 2004 has presented models that support the hypothesis towards the formation of long-lived giant gaseous protoplanets.…”

“…Considering the grain segregation process suggested by Boss (1998a), Nayakshin (2010) estimated the process analytically as well as performed simple spherically symmetric radiation hydrodynamic simulations to test the ideas. Both analytic model and numerical simulation due to Nayakshin (2010) confirmed the suggestion made by Boss (1998a) but the initial configurations predicted by this study are found to be different from the ones found in the study of Helled and Schubert (2008). Podolak (2003) and Movshovitz and Podolak (2008) calculated the Smoluchowski equation based on more detailed physics of grains and investigated grain growth and sedimentation in the envelope of a protoplanet.…”