Giant Planet Formation by Gravitational Instability

“The other one is disk instability model (Boss 1997), a top-down process that directly forms through the gravitational collapse of a protoplanetary disk.”

“…mechanisms have been proposed to explain these various architectures such as core accretion ( e.g., Pollack et al. 1996 ) , pebble accretion ( e.g., Lambrechts & Johansen 2012 ) , disk gravitational instability ( e.g., Boss 1997 ) , and fragmentation of a protostellar disk ( e.g., Bate 2009 ) .”

“This leads researchers to conduct more research on the estimation of initial structures of the protoplanets formed by the GI envisioned by Boss [9], and planetary formation through this mechanism is still a subject for ongoing research.”

“Core accretion, disk instability, migration, and disk evolution mechanisms are capable of producing planets up to40MJup (Pollack et al. 1996; Boss 1997; Alibert et al. 2005; Mordasini et al. 2009), explaining the formation of some brown dwarf companions.”

“…E-mail: skundu@syr.edu † E-mail: ecoughli@syr.edu ‡ E-mail:youdin@arizona.edu § E-mail:philip.armitage@stonybrook.edu 1 The other paradigm for giant-planet formation is through instabilities in the protoplanetary disk – the “disc instability”model (e.g., Cameron 1978;Adams et al. 1989; Boss 1997).”

“Gravitational instability within a protoplanetary disc is an alternative theory for giant planet formation in protoplanetary disc (Boss 1997) and may have similar implications for satellite formation in a circumplanetary disc.”

“1 and Q decreases as R increases (e.g., Boss 1997; Johnson & Gammie 2003).”

“As the result of the perceived need to create a concurrent formation theory for both gaseous and rocky objects in the solar system, the "disk instability" model [61], [62], [63]—where gas giant protoplanets form rapidly through a gravitational instability of the gaseous portion of the disk—has been neglected and the "…”

“By contrast, the disk instability model (Boss 1997) suggests no such restriction.”

“…theories are the so-called core accretion model which is efficient in the inner region of a PPD (e.g., Mizuno 1980; Stevenson 1982; Pollack et al. 1996) and gravitational instability (GI) which operates mainly in the outer regions (e.g., Adams et al. 1989; Boss 1997; Boley 2009; Rafikov 2009).”

“Gravitational instability, for instance, may eventually lead to giant planet formation at the outer parts of a PPD (Boss 1997; Rafikov 2005; Forgan & Rice 2013; Boss 2017), whereas the core accretion theory is believed to be the dominant planet formation mechanism at the inner regions of a PPD…”

“There are two known mechanisms for the formation of the condense proto-planetary entities through the protostellar accretion disks: the core accretion (Goldreich & Ward 1973, Miguel & Brunini 2009), and the disk instability (Toomre 1964, Boss 1997, Zhu et.al.”

“In contrast and following Boss (1997, 2001, 2002, 2003, 2008), Mayer et al. (2002, 2004), Griv & Gedalin (2005), Griv (2006) and Durisen et al. (2007), we suggest that all the planets around the Sun were created simultaneously by the disc’s gravitational instability, assuming no migration of…”

“Indeed, the massive, long-period planets detected by direct imaging have been suggested to be evidence of planet formation via gravitational collapse [14, 36].”

“…≡ M BD / M � < 0.01 ) and BD masses below approximately 42.5 M Jup exhibits properties broadly consistent with formation through gravitational instability within protoplanetary disks ( A. P. Boss 1997; I. A. Bonnell et al. 2008; D. Stamatellos & A. P. Whitworth 2009; K. Kratter & G. Lodato 2016 ) .”

“It is generally accepted that giant planet formation occurs primarily through two main scenarios: core accretion (CA; Safronov 1972; Goldreich & Ward 1973; Hayashi et al. 1985; Mizuno 1980; Pollack et al. 1996) and gravitational instability (GI; Kuiper 1951; Boss 1997).”

“…mechanism may be consistent with some rare wide-orbit giant planets (J. Cadman et al. 2021; J. Speedie et al. 2024), but this theoretical framework struggles to make planets except under special conditions (A. P. Boss 1997; W. K. M. Rice et al. 2003; Z. Zhu et al. 2012; H. Deng et al. 2021).”

“Since the physical conditions of protoplanetary disks profoundly influence the planet formation processes (Boss 1997; Kornet et al. 2005; Mordasini et al. 2012; Mulders et al. 2015a, 2015b; Narang et al. 2018), a comprehensive understanding of the disk properties is crucial for developing planet…”

“Although fragments continue to accrete and grow after their formation, as shown in Figure 5, the relatively low initial masses suggest that these fragments can potentially evolve into gas giants (e.g., A. P. Boss 1997; A. C. Boley et al. 2010).”

“Two primary models are considered: • Gravitational instability (GI) and/or turbulent fragmentation : This mechanism involves the direct collapse of disk material into giant planets, primarily in the outer regions of massive disks (Boss 1997).”

“GI (Boss 1997; Kratter and Lodato 2016) occurs when locally disc self-gravity is important with respect to stellar gravity.”

“According to the other school of thought, the giant gaseous protoplanets can be formed due to the disk instability in the surrounding disk of the parent star [3, 4].”

“An alternative to core accretion is gravitational instability (Zel’Dovich, 1970; Boss, 1997).”

“As suggested by previous studies (Adams et al. 1989; Boss 1997; Kratter et al. 2010; Zhu et al. 2012; Forgan & Rice 2013; Kratter & Lodato 2016), planets, brown dwarfs, and binary companions may form through disk fragmentation when a disk is gravitationally unstable.”

“Massive substellar companions may then likely form by these mechanisms [36, 41, 42] in the same separation range than planets but on a much shorter timescale than the usual core accretion mechanism invoked for planets [43–45], provided suitable conditions exist.”

“Such a system configuration requires that Jupiter and Saturn have formed very early, possibly via the disk instability mechanism (or G.I.), which predicts that giant planets form through the clumping and collapse of the gaseous protoplanetary disk (Boss 1997).”

“Dans le premier, les planètes géantes se forment par instabilité gravitationnelle dans le disque protoplanétaire [Boss, 1997].”

“Conversely, this large heavy material enrichment clearly excludes the gravitational instability scenario (Boss 1997).”

“In the second one, a gravitationally unstable region in a protoplanetary disk forms self-gravitating clumps of gas and dust (Boss 1997).”

“This is a widely accepted formation scenario of protoplanets (e.g., Boss 1997; Mayer et al. 2004) because it can take place in short time scales.”

“In this sense, this mechanism is particularly useful if we consider the recently ressurected gravitational instability model (Boss 1997) for the formation of Jupiter and possibly Saturn.”

“directly from the disc in the early period of the circumstellar disc evolution ( Boss, 1997, 2002, 2004; Mayer et al., 2002).”

“…protoplanetary disks (we refer to them as “embedded disks”) which can become gravitationally unstable (e.g., Laughlin and Bodenheimer 1994; Boss 1997; Durisen et al. 2007 and references therein; Boley and Durisen 2008; Vorobyov 2011) and which represent the starting point of our final…”

“Two different scenarios are currently being debated in the planetary community to explain the process of formation of gaseous planets: the core accretion model (Safronov 1969; Goldreich and Ward 1973; Pollack et al. 1996) and the gravitational instability model (Cameron 1978; Boss 1997).”

“Proposed formation scenarios include gravitational instability in a massive circumstellar disk ( A. P. Boss 1997 ) , core accretion with subsequent dynamical scattering ( e.g., F. A. Rasio & E. B. Ford 1996; D. Veras et al. 2009 Finley et al. 2026 ) .”

“While core accretion ( J. B. Pollack et al. 1996 ) can proceed in a wide range of protoplanetary disks, gravitational instability ( A. P. Boss 1997 ) is thought to operate only in the most massive and unstable systems, where self-gravity drives spiral arms that may subsequently fragment into bound…”

“Boss (1997) proposed gas fragmentation as a way to rapidly form planets in the outer disc.”

“Mechanisms such as disk gravitational instability ( A. P. Boss 1997; D. Stamatellos & A. P. Whitworth 2009; J. C. Morales et al. 2019; H. Deng et al. 2021; A. P. Boss & S. Kanodia 2023 ) and planetary collisions ( M. Pan et al. 2024 ) have been proposed to resolve this paradox.”

“Under this picture, disk instability (Boss 1997) better explains the formation of γ Cep Ab because, unlike core accretion, this mechanism would have sufficient time to generate the planet before the disk was disrupted.”

“…is particularly common for wide-separation brown dwarfs, where stellar-like formation pathways such as turbulent fragmentation or gravitational instability are expected to produce companions that inherit the elemental composition of their host stars ( A. P. Boss 1997; A. G. W. Cameron 1978 ) .”

“The rapid formation of such large bodies would have to proceed through either the streaming instability or gravitational instability ( GI; A. P. Boss 1997; A. N. Youdin & J. Goodman 2005 ) .”

“Unlike giant planets, brown dwarfs do not form more readily around metal-rich stars, pointing to a distinct formation pathway such as gravitational instability ( A. P. Boss 1997; G. Chabrier et al. 2014; B. P. Bowler et al. 2020 ) .”

“…in situ , near their present-day orbits, either through gravitational instability – the fragmentation of the protoplanetary disk into bound clumps (Boss 1997) – or through core accretion, in which a solid core grows and accretes a massive gaseous envelope (e.g., Perri & Cameron 1974; Pollack et…”

“Direct collapse of molecular cloud cores or fragmentation of massive protostellar disks can produce brown dwarfs through stellar-like formation processes ( Boss 1997; Bate 2014 ) .”

“In contrast, low-mass BDs may also arise from disk-based processes such as gravitational instability ( A. G. W. Cameron 1978; A. P. Boss 1997 ) or the core accretion mechanism ( J. B. Pollack et al. 1996; B. Ma & J. Ge 2014; K. Kratter & G. Lodato 2016 ) as giant planets.”

“Conventional wisdom holds that gas giants formed by gravitational instability of the gas in a protoplanetary disk ( e.g., A. P. Boss 1997, 2025; R. H. Durisen et al. 2007 ) should lead to atmospheres with C / O ratios similar to those of their host stars.”

“…to the formation of terrestrial and giant planets cores and the improvement of core-accretion (Ida & Lin 2004; Matsuo et al. 2007) and disk-instability (Boss 1997; Currie et al. 2022) scenarios, which should be adopted to model the ensuing evolution and accretion of a primary atmosphere.”

“First, disk instability—which is less sensitive to metallicity than core accretion ( A. P. Boss 1997 ) —may operate more efficiently in thick disk protoplanetary disks, bypassing the solid-assembly bottleneck entirely.”

“The predicted time available for planet formation di ff ers between the two main planet formation paradigms: core accretion (Pollack et al. 1996, Alibert et al. 2005) and gravitational instability (Boss 1997, Durisen et al. 2007).”

“The two most widely accepted scenarios for planet formation are the core accretion (CA, Mizuno, 1980; Pollack et al., 1996) and the gravitational instability (GI, Cameron, 1978; Boss, 1997) models.”

“1 M ⋆ ) protostellar discs (Kuiper 1951; Cameron 1978; Boss 1997; Rice et al. 2003; Stamatel-los et al. 2007a; Boley 2009; Rice 2022) provides an alternative mechanism to core accretion (e.g. Goldreich & Ward 1973; Dr˛a˙zkowska et al. 2023) for the formation of gas giant planets.”

“The discovery of four distant giant planets around HR 8799 by direct imaging suggests that gravitational instability (Boss 1997) would play an important role in a planet formation (Marois et al. 2008, 2010).”

“It has been suggested that such objects may form in situ by the fragmentation of massive, self-gravitating disks (Boss 1997, 2011; Vorobyov 2013) by the direct collapse of molecular cloud material (Boss 2001), or by core- or pebble accretion (Lambrechts & Johansen 2014) and subsequent outwards…”

“Substituting for r and∞,then we have [8].”

“Au sein de ce disque, pourraient également exister des proto-planètes gazeuses formées par effondrement gravitationnel au même moment que l’étoile (BOSS, 1997).”

“One possible alternative to form giant planets at large orbital separation is by gravitational instabilities (Boss, 1997), which likely operate, in parallel with the core accretion, in the outer disk during the early stages of disk evolution.”

“…et al., 1996), a pathway which is expected to be the dominant method of planet formation in the inner 10 AU, and (2) gravitational collapse via disk instability (Cameron, 1978; Boss, 1997), which might be the mechanism of planet formation at separations from 10 – 100 AU (Rafikov, 2007, 2011).”

“• Disc instability theory (Kuiper, 1951; Cameron, 1978; Boss, 1997) has giant planets rapidly forming via the gravitational fragmentation of an unstable PP disc, similar to Safronov–Goldreich–Ward theory of planetesimal formation (Section 3.”