Giant Planet Formation, Evolution, and Internal Structure

Abstract

The large number of detected giant exoplanets offers the opportunity to improve our understanding of the formation mechanism, evolution, and interior structure of gas giant planets. The two main models for giant planet formation are core accretion and disk instability. There are substantial differences between these formation models, including formation timescale, favorable formation location, ideal disk properties for planetary formation, early evolution, planetary composition, etc. First, we summarize the two models including their substantial differences, advantages, and disadvantages, and suggest how theoretical models should be connected to available (and future) data. We next summarize current knowledge of the internal structures of solar- and extrasolar- giant planets. Finally, we suggest the next steps to be taken in giant planet exploration.Comment: Accepted for publication as a chapter in Protostars and Planets VI, to be published in 2014 by University of Arizona Pres

Planet formation from the ejecta of common envelopes

“…Spiral structures start appearing at Q ∼ 1.7, while fragmentation occurs for Q ∼ 1 (Durisen et al 2007;Helled et al 2013). When this stage is reached, turbulence and shocks are expected to develop, providing a heating mechanism that may compensate for the cooling of the disk (Gammie 2001).…”

“…In particular, they may rapidly migrate inward (Baruteau et al 2011;Michael et al 2011;Zhu et al 2012), which can lead to a complete destruction due to tides (Boley et al 2010;Nayakshin 2010) or to changing boundary conditions (Vazan & Helled 2012). In addition, growth may be delayed by the formation of a circum-protoplanetary disk (Ayliffe & Bate 2012;Helled et al 2013). While a detailed treatment of such effects is beyond the scope of this work, we assume here that the inward migration stops if the planetary masses are higher than the gap-opening mass M gap , implying that the orbit of the planet can be cleared from gas, thus strongly reducing the effect of dynamical friction.…”

“…A CE is defined as a structure where two stars share the envelope. One of them is typically a giant, for instance in an AGB phase (Herwig 2005), while the companion can be a white dwarf or a mainsequence star. In this phase, the orbital period decreases due to gravitational drag and tidal interactions (e.g., Iben & Livio 1993;Kashi & Soker 2011), while both the energy and angular momentum of the companion are injected into the envelope.…”

Direct Detection of Precursors of Gas Giants Formed by Gravitational Instability With the Atacama Large Millimeter/Submillimeter Array

“…Also, Stamatellos et al (2011) included an approximate treatment of radiative transfer and focused on detectability by IRAM. The limited treatment of radiation can enhance fragmentation and the masses of clumps (Rogers & Wadsley 2011;Helled et al 2014) as well as affect the resulting temperature structure in the disk Boley et al 2006;Evans et al 2015), and hence any inference concerning detectability.…”

“…Whether disk fragmentation is a common outcome of GI and results in long-lived objects that contract to become gas giant planets (Mayer et al 2004;Boss 2005), or even lower mass planets via tidal mass loss Galvagni & Mayer 2014), is still debated (Helled et al 2014). However, disk instability offers a natural explanation for the massive planets on wide orbits discovered via imaging surveys in the last decade (e.g., Marois et al 2008) because the conditions required for disk fragmentation, namely a Toomre instability parameter Q < 1.4 and short radiative cooling timescales, should be satisfied in the disk at R > 30 au Rafikov 2007;Clarke 2009;Meru & Bate 2010).…”