Giant Planet Formation by Gravitational Instability

“…(Springel et al. 2005), star formation by a gravitational instability (Wang and Silk 1994), giant planet formation by a gravitational instability (Boss 1997), solar flares by magnetic reconnection instabilities (Priest and Forbes 2000), such as by the kink-mode or tearing mode instability, solar…”

“On the one hand, our results may be considered a point in favor of very rapid giant planet formation through gravitational instability (Boss 1997).”

“Giant planet formation (top-down model) In the fragmentation scenario, giant planets form directly from the protoplanetary disk via a gravitational instability (Boss, 1997), which causes a patch of gas and dust to collapse under its own gravity and form a massive planet.”

“y et al., 2005). This has stimulated interest in the possibility that giant planets, both solar and extrasolar, may have formed in 103-4 yr from gravitational instabilities in the protostellar disks (Boss, 1997, 2002; Mayer et al., 2002). Given Jupiter’s size and proximity to the asteroid belt, it seems plausible that…”

“Boss (1997, 1998) was the first to revive the idea that such clumps could become permanently bound and evolve into gas giant planets.”

“…potentially precipitated by infalling material, may drive spiral arm formation as well as the formation of tail-like structures through gas clumps ejected when the disk fragments (e.g., Boss 1997; Gammie 2001; Vorobyov & Basu 2005; Kratter et al. 2008; Harsono et al. 2011; Vorobyov et al. 2020).”

“Opposed to this core formation scenario is the gravitational instability scenario, in which gas giants are thought to form directly from a dense disk by gravitational instability (Boss 1997; Boley et al. 2010).”

“…including formation of giant planets by gravitational instability (<1Myr; The Astronomical Journal, 155:54 (26pp), 2018 February Ward-Duong et al. Boss 1997) or core accretion (∼10Myr; e.g., Pollack et al. 1996), the onset of terrestrial planet formation (∼3–10Myr; Chambers & Wetherill…”

“The observation of a large core in such a metal-rich systemwould seem to support the core accretion theory as opposed to coreless alternatives such as gravitational instability (Boss 1997).”

“…core accretion (Mizuno 1980; Bodenheimer & Pollack 1986; Pollack et al. 1996), in which a rocky or icy core reaches a critical mass and rapidly accretes an envelope of gas, or gravitational instability (Boss 1997), in which the massive, cool disk fragments and collapses into giant planets.”

“If they fragment, a number of objects may potentially form out of discs of different sizes including stars (e.g. Nayakshin et al. 2007), brown dwarfs (e.g. Stamatellos et al. 2007) and planets (e.g. Boss 1997; Mayer et al. 2002).”

“…these are formed in situ through gravitational instability, either through interstellar cloud fragmentation or circumstellar disk fragmentation (Boss 1997; Kroupa 1995), or whether they were formed closer to the star through accretion processes (Pollack et al. 1996) and migrated outward later…”

“C-0265. generally believed to form through core accretion (Pollack et al. 1996; Alibert et al. 2005) or gravitational instabilities in the circumstellar disk (Cameron 1978; Boss 1997).”

“This model is known as gravitational instability (Kuiper 1951; Boss 1997), and states that planets form from the collapse of gas into clumps by self-gravity.”

“Planet formation pathways, such as disk instability or core accretion, could in principle allow to form bodies up to 40 MJ within protoplanetary disks (Pollack 1996, Boss 1997, Ida & Lin 2004, Alibert et al. 2005, Mordasini et al. 2009).”

“In the two scenarios, core accretion (Pollack et al. 1996) and gravitational instability (Boss 1997), the planets form within the primordial gas disk.”

“On the other hand, the so-called disk instability models advocate that giant planets can be formed by the direct collapse of gas and dust in the proto-planetary disk (Boss 1997).”

“Giant planets may be forming at thismoment (Lissauer 1993; Pollack et al. 1996; Boss 1997; Ida & Lin 2004).”

“…disks as massive as 0.1 M⊙), it is becoming clear that at least some protoplanetary disks are likely to have experienced a phase of gravitational instability, which might have led to the rapid formation of gas giant planets by the disk instability mechanism (e.g., Boss 1997; Mayer et al. 2002).”

“…gas accretion onto cores with ∼ 10 Earth masses that are themselves assembled out of planetesimals (Mizuno 1980; Pollack et al. 1996), or through gravitational collapse when protostellar disks become cold and/or dense enough to be locally gravitationally unstable (Boss 1997; Mayer et al. 2002).”

“Here, only the most recent results will be addressed, specifically focusing on Boss (1997) , for the gravity instability model, and Pollack et al. (1996) and Wurchterl (1991), for the core accretion/instability model.”

“…radii, coupled with evidence of a high disc mass (∼0.1–0.13 M ; Guilloteau et al. 2011; Kwon et al. 2011) has seen gravitational instability (GI; Boss 1997) being invoked to explain both the observed dust structures in HL Tau (Akiyama et al. 2016; Takahashi & Inutsuka 2016), along with the…”

“An alternative theory of planet formation is disc instability, that is, planet formation by the gravitational fragmentation of young protostellar discs (Kuiper 1951; Cameron 1978; Boss 1997).”

“…1996; Alibert et al. 2005; Dodson-Robinson et al. 2009; Lambrechts & Johansen 2012) or via gravitational instabilities of the protoplanetary disc (Boss 1997; Rafikov 2005; Durisen et al. 2007; Kratter, Murray-Clay & Youdin 2010; Boss 2011) this must have happened closer to the star and after…”

“…relation in the giant planet regime supports the core accretion model (e.g., Ida & Lin 2004; Mordasini et al. 2009) rather than the disk instability model (e.g., Boss 1997, 2002) as the preferred mechanism for giant planet formation within a few AU separation from the star (Johnson et al. 2010).”

“…1969; Stevenson 1982), our 1σ confidence interval extends down to zero core mass and therefore does not preclude alternative formation models such as disk instability (e.g., Boss 1997), nor does it provide a definitive test of post-formation core erosion (e.g. Stevenson 1982; Guillot et al. 2004).”

“Disks are critical structures in the star and planet formation process, as they provide a conduit to channel material onto the central object (e.g., Hartmann 1997) and supply a reservoir of dust and gas to form planets (e.g., Pollack et al. 1996; Boss 1997).”

“…that other systems are truly different, with large relative orbital inclinations, which could point to either an early, chaotic phase of orbital evolution or formation by another mechanism such as disk instability (Kuiper 1951; Cameron 1978; Boss 1997, 2000; Boss, Wetherill, & Haghighipour 2002).”

“In this case, lower mass brown dwarfs may form similar to giant planets via core accretion (Pollack et al. 1996) or disk instability (Cameron 1978; Boss 1997) and higher mass brown dwarfs may form similar to stars from gravitational collapse and turbulent fragmentation of molecular clouds (Padoan &…”

“Disc fragmentation through gravitational instability hasbeen considered a potential formation channel for giant planetsand very low mass stars for some time (Cameron 1978; Boss 1997).”

“…and evolution, because they provide an indication of the planet internal heat, structure and composition, as well as the heating mechanism for those which undergo strong tidal effects and stellar irradiation, allowing the discrimination between competing theories (Pollack et al. 1996; Boss 1997).”

“When gases dominate, collapse is predicted to form giant gaseous protoplanetesimal cores that drive further accretion of gas (Boss 1997).”

“An alternative to core accretion is the formation of GEMS in the protostellar phase, i.e., in Class 0, I disks (or protostars) through gravitational instability (GI; Kuiper 1951; Cameron 1978; Boss 1997).”

“Such high mass objects on the planet-brown dwarf boundary are thought to form by one of two general formation pathways: core accretion (Pollack et al. 1996) or gravitational instability (Boss 1997).”

“In the context of protoplanetary disks, this is one possible origin of gas giants (Boss 1997; Durisen et al. 2007), but in AGN disks, it is generally thought to lead to star formation.”

“Gravitational instability (GI) has been proposed as a trigger for spiral arms in massive disks, which can subsequently fragment and form clumps (e.g., Boss 1997; Gammie 2001).”

“The two leading models for giant gas planet formation are core accretion (Pollack et al. 1996; Kenyon & Bromley 2009) and formation through gravitational instability in the protoplanetary disc (Boss 1997).”

“Core accretion is the dominant formation channel at small separations of .10 AU (Pollack et al. 1996; Alibert et al. 2005), while disk instability (Boss 1997) and turbulent fragmentation (Bate 2009) operate on wider orbits at tens to hundreds of AU.”

“In a protoplanetary disks self-gravitating clumps can form from the fragmentation of spiral arms in Toomre unstable disks (Boss 1997; Mayer et al. 2002).”

“…instability model in which gaseous planets are formed as a result of gravitational instabilities in the disk surrounding the young star (e.g., Boss, 1997; Mayer et al., 2007), might be required to explain the formation of massive gaseous planets at very large radial distances, the existence…”

“Such objects pose strong constraints to the possibility of planet formation via gravitational instability (Boss 1997, 2003), and also suggest that strong and global grain growth may not always be efficient.”

“Recently, Boss (1997) revisited a model originally proposed by Cameron (1978), the ’core collapse scenario’, in which a giant planet is formed in much the same way as a star through a gravitational instability in the disk.”

“…of young objects (Fortney et al. 2008; Spiegel & Burrows 2012), with core-accretion scenarios (Pollack et al. 1996) leaving planets with lower initial entropies (“cold-start” models) than gravitational instability (Boss 1997) or turbulent fragmentation (Bate 2009) routes (the “hot-start” pathway).”

“If a massive gaseous disk becomes gravitationally unstable and fragments into a number of self-gravitating bound structures (Boss 1997), these structures can then further collapse to become giant planets or brown dwarfs.”

“Gravitational instability (GI) in a protoplanetary disk can result in the formation of massive companions at separations of hundreds of astronomical units from the central star (Boss 1997).”

“The metallicity dependence is typically interpreted as support for the core accretion model of giant planet formation (Pollack et al. 1996) while in the rival disc instability model (Boss 1997) no such correlation is expected.”

“…et al. 2004; Fischer & Valenti 2005) as well as the lack of a metallicity correlation in low-mass planet hosts (e.g. Mayor et al. 2011; Cassan et al. 2012; Howard et al. 2013) and ii) disc instability models which do not depend on the metallicity of the primordial disc (Boss 1997, 2002, 2006).”

“…that if these discs are sufficiently unstable while t ey are self-gravitating, they may fragment into bound objects, providing a mode of planet formation in protostellar discs (Kuiper 1951; Cameron 1978; Boss 1997) or star formation in AGN discs (Levin & Beloborodov 2003; Nayakshin & Sunyaev 2005).”

“…even have companions in the brown dwarf or low stellar mass regime, suggesting that their likely formation through gravitational instability (Boss 1997, 2003, 2011; Vorobyov 2013) is compatible with the formation of massive Kuiper belt analogues, e.g. HR 2562 (Konopacky et al. 2016), HD…”

“…on the planet’s formation (e.g. Owen et al. 1999; Gautier et al. 2001; Lodders 2004; Guillot and Hueso 2006; Mousis et al. 2012, 2019), now favoring the core accretion scenario for these planets (Pollack et al. 1996; Hubickyj et al. 2005) over the disk instability scenario (Boss 1997, 2002).”

“Furthermore, the competing paradigm of planet formation, gravitational instability (e.g., Boss 1997), may yet play a role in any unified theory of planet formation (e.g., Forgan & Rice 2013).”

“Jupiter forms within a thousand years from one of the fragments (Boss 1997; Durisen et al. 2007).”

“Alternatively, a gravitational instability in the disk that occurs on a timescale of 1000 yr and results in amore rapid condensation, to form a giant planet in 0.1 Myr (Cameron 1978; Boss 1997, 1998), could have occurred by the Class I stage.”

“In analogy with models for planet formation in protostar accretion disks (e.g., Boss 1997; Lodato & Rice 2004; Chen et al. 2023) or star formation in accretion disks around supermassive black holes (e.g., Levin 2003; Goodman & Tan 2004), cooling-induced fragmention in gravitationally-unstable…”

“…times its mass in gas from the proto-planetary disk (e.g., Perri & Cameron 1974, Pollack et al. 1996; see Chabrier et al. 2014 for a review), or gravitational instability, in which part of the proto-planetary disk fragments into bound clumps (e.g., Boss 1997; see Durisen et al. 2007 for a review).”

“Two formation mechanisms are typically considered for giant planets: gravitational instability (GI, Kuiper 1951; Boss 1997), and core accretion (CA, Perri & Cameron 1974; Mizuno et al. 1978; Bodenheimer & Pollack 1986).”

“…disk where they formed, their initial location in the disk, and the accreted materials during the evolution history (e.g., Pollack et al. 1996; Boss 1997; Alibert et al. 2005; Madhusudhan et al. 2011; Helling et al. 2014; Kreidberg et al. 2014a; Mordasini et al. 2016; Thorngren et al. 2016…”

“Their formation via core-accretion (Pollack et al. 1996) is unlikely (e.g., Rafikov 2011) but in principle they could form via gravitational instability (Boss 1997).”

“…orbits of tens of AU to a few hundred AU, gas giants may assemble from pebble accretion (Lambrechts & Johansen 2012) or fragment directly from gravitational instabilities in massive protoplanetary disks during the earliest phases of disk evolution (e.g., Boss 1997; Stamatellos & Whitworth 2009).”

“The theory is an offspring of the GI model for planet formation (e.g. Cameron et al. 1982; Boss 1997) but is far richer in terms of physics included C© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society at U niversity of L eicester on O ctober 14,…”

“In addition to core accretion, gravitational instability (GI) has also been proposed as a formation mechanism for giant planets (Boss 1997; Durisen et al. 2007).”

“With our chosen parameters, the disks should be very stable against gravitational instabilities that may aid planet formation (e.g. Boss 1997, 2003; Rice et al. 2006).”

“The probability of forming giant planets according to the disk instability model (e.g., Boss 1997, 2000; Mayer et al. 2004), however, is remarkably insensitive to the primordial surface density of solids of the protoplanetary disk (Boss 2002; Rice et al. 2003), thus planet occurrence should not be…”

“An important unknown for young disks is the temperature structure because this governs whether they are gravitationally unstable and thus capable of forming planets through gravitational instabilities (e.g., Boss 1997; Boley 2009) or prone to luminosity outbursts (Vorobyov 2009).”

“…generally to offer greater leverage on the relative importance that core accretion (Mizuno et al. 1980) and disc gravitational instabilities (Boss 1997) play in formation and the various migration mechanisms play in the evolution E-mail: baileyji@umich.edu of so-called hot Jupiters (e.g.…”

“Indeed, the properties of HIP 64892B raise the possibility that it formed via gravitational instability, either through a binary-star mechanism or through disk instability in the circumstellar disk of the primary (Boss 1997).”

“There are two competing theories for giant planet formation: core accretion (CA; Mizuno 1980; Pollack et al. 1996), which is the standard one, and disk instability (DI; Cameron 1978; Boss 1997).”

“Boss (1997) began the detailed study of DI with 3D models that used simplified thermo- dynamics for the gaseous disk, namely isothermal or adiabatic gas pressure laws.”

“One of the open questions is the selfgravitational instability (Toomre 1964) of protoplanetary discs, which may (Kuiper 1951; Boss 1997) or may not (e.g., Kumar 1972; Goldreich & Ward 1973; Laughlin & Bodenheimer 1994) lead to formation of gas giant planets by fragmentation of the discs on clumps…”

“These companions are on orbits too large for in situ formation by either core accretion (Pollack et al. 1996; Alibert et al. 2005) or gravitational instability within protoplanetary disks (Cameron 1978; Boss 1997).”

“The disks are believed to be the place where the planets form (Boss 1997; Mayer et al. 2002), and are composed of a mixture of gas and dust with a wide range of grain composition (Henning & Meeus 2009).”

“…are typically a few Myr (Haisch et al. 2001), the idea of creating giant planets in a few orbital times via gravitational instabilities was revived (Boss 1997) and has since been the subject of sustained interest (Boss 2002, 2008; Mayer et al. 2004, 2007; Pickett et al. 2000; Pickett & Durisen…”

“This scenario of planet formation has been explored by Boss (1997, 2001) and recently by Mayer et al. (2002).”

“In the Gravitational Instability (GI) scenario (Boss 1997; Durisen et al. 2007), giant planets originate from gas clumps that form in a gravitationally unstable PPD by direct collapse.”

“…disc and coagulate to form rocky planets, with subsequent accretion of gas to create gas giants, and (2) gravitational instability (e.g. Adams et al. 1989; Boss 1997; ⋆ E-mail: cjn@leicester.ac.uk Durisen et al. 2007; Nayakshin 2017), where the protoplanetary gas disc fragments into gaseous clumps.”

“…planets at long orbital periods (even around low-metallicity stars) might be explained if they are mainly formed by gravitational instabilities in the disc (e.g. Dodson-Robinson et al. 2009), a mechanism that does not depend on the metallicity of the primordial disc (Boss 1997, 2002, 2006).”

“McCrea & Williams (1965) showed that microscopic grains grow and sediment to the centre of such gas clumps within a few thousand years, presumably forming a massive solid core there (cf. also Boss 1997, 1998).”

“Giant planets, on the other hand, can form via core accretion in a disk fairly close to the star (Pollack et al. 1996; Kenyon & Bromley 2009) or via gravitational instability at larger separations so long as the disk is sufficiently massive (Boss 1997).”

“Disc fragmentation has been touted as a possible process for forming brown dwarfs and gas giant planets (Boss 1997; Stamatellos et al. 2007).”

“Gravitational disk instability can form objects as low in mass as Jupiter (Boss 1997; Boss & Kanodia 2023), while core-nucleated accretion can form objects as massive as 10 M J under the right conditions (Mordasini et al. 2012), blurring the boundary.”

“Therefore, super-Jovian compan-ions are not easily compatible with formation via either in-situ core accretion or gravitational collapse (Pollack et al. 1996; Boss 1997; Chabrier 2003; Kratter & Lodato 2016).”

“This underscores the importance of local dust enhancement 29,30 or alternative pathways, such as outward migration 31 or gravitational fragmentation 32 .”

“…by the physics of the planet formation process, that is, classical core accretion (Pollack et al. 1996; Ida & Lin 2004), gravitational instability (Boss 1997), or pebble accretion (Johansen & Lacerda 2010; Ormel & Klahr 2010; Bitsch et al. 2015), but also reflects dynamical re-structuring…”

“…(e.g. Johnson & Gammie 2003; Stamatellos & Whitworth 2009; Cossins et al. 2010; Baehr & Klahr 2015; Riols & Latter 2016), and especially for protoplanetary discs by many authors mostly motivated by the formation of gas giants via GI (Boss 1997, 1998; Durisen et al. 2007; Zhu et al. 2012).”