A Decreased Probability of Habitable Planet Formation around Low‐Mass Stars

“The average distance of the HZ from the parent star depends primarily on the star’s luminosity, and is closer-in and narrower around lowermass stars (Kasting et al. 1993).”

“For a planet to remain habitable, it must control its surface temperature over long timescales, possibly via the CO2-carbonate cycle (Walker et al. 1981), which is enabled by a relatively thick atmosphere, a hydrological cycle, and active plate tectonics.”

“We integrated each simulation for 200 Myr using the hybrid integrator Mercury (Chambers 1999).”

“…M⋆, f is a scaling factor for the disk (f=1 for MMSN), Z is the stellar metallicity (1.0=solar), and α moderates the steepness of the density profile (α = 3/2 in the MMSN model; Hayashi 1981, but more recent reconstructions using an accretion disk model as a constraint gives α = 1/2; Davis 2005).”

“There also exists a factor of 3-5 range in metallicity for thin-disk stars (Nordstrom et al. 2004), which adjusts the effective gas-to-dust ratio.”

“…in situ from a very massive disk, with fZ ∼ 30− 50; or 2) our assumption of in situ formation failed in this case: the planets of Gl 581 formed farther from the star (probably in the icy regions of a relatively massive disk, with fZ of at least 5-10) and migrated inward (Goldreich & Tremaine 1980).”

“2004; Fischer & Valenti 2005) allow for 70-90% of stars to have planetary systems without Jovians, and an even larger fraction for lower-mass stars (Endl et al. 2006; Butler et al. 2006).”

“The most promising lead comes from estimates of outer disk masses using submm and mm techniques (Beckwith et al. 1990), which remain uncertain because of adopted dust temperatures, opacities, distances, and radiative transfer model.”

“…HZs of lower-mass stars – is inefficient dynamical stirring in the low-mass disks found around low-mass stars, because more massive embryos are needed to increase eccentricities enough for significant radial mixing and therefore water delivery (Morbidelli et al. 2000; Raymond et al. 2004, 2007).”

“…of short-period Earth-sized planets around UCDs and further constrain planet formation theories, which currently predict UCD planets ranging from metal-rich Mercury-sized planets to volatile-rich Earth-sized planets (e.g., Raymond et al. 2007; Montgomery & Laughlin 2009; Miguel et al. 2020).”

“Similar outcomes were reported by Kokubo et al. (2006) and by Raymond et al. (2007) and Ciesla et al. (2015) in looking at the formation of planetary systems around stars of different masses: greater numbers of smaller planets were produced around stars that had lower protoplanetary disk masses.”

“However, the simulations of Raymond et al. (2007a) show that the fraction of water delivered by planetesimals is much larger than the one delivered by embryos4.”

“It is reasonable to expect that many planets in or near the habitable zone of M dwarfs will be fairly dry due to reduced volatile delivery (Raymond et al. 2007) and nightside ice trapping (Menou 2013).”

“The dynamically hot evolution of protoplanets would affect the water delivery of planets by planetesimals since the ice line location is close to the central star around low-mass stars (Ida & Lin 2005; Raymond et al. 2007).”

“Studies suggest that rocky planets form in 10 - 100 million years (Chambers, 2004; Raymond et al., 2007, 2013; Kleine et al.,2009), so planets in M dwarf habitable zones are subjected to extreme luminosities early on for an extended period of time.”

“This is particularly the case for planets detected around brown dwarfs and very-low-mass stars (e.g. Payne & Lodato 2007; Raymond et al. 2007; Kopparapu et al. 2017).”

“For an estimate on the lower limit of the mass range see Raymond et al. (2007).”

“Simulations by Raymond et al. (2007) also show that it is difficult to form planets larger than 0.3 M ⊕ so close to a low-mass star.”

“Raymond et al. (2007) and Lissauer (2007) found that planets formed in situ around low mass stars may be deficient in volatiles, as water-bearing planetesimals would not be scattered as often from beyond the snow line.”

“This has led to a long debate regarding the origins and timing of the delivery of water to the Earth (Morbidelli et al. 2000; Raymond et al. 2007; Izidoro et al. 2013).”

“In particular, Raymond et al. (2007) performed N-body simulations to study the process of terrestrial-like planet formation to a wide range of stellar masses (0.2 M .”

“…et al., 2014), 2) in situ accretion of planetesimals that formed there or have migrated from outer regions due to aerodynamical gas drag (e.g., Raymond et al., 2007; Chiang & Laughlin 2013), 3) in situ accretion of protoplanets that have migrated from outer regions due to type I migration…”

“These models are of interest for exploring how conditions might vary between disks around G dwarfs and M dwarfs, with possible ramifications for the habitability of any rocky planets that form (e.g., Raymond et al. 2007) around M dwarfs.”

“The relation between the mass of hosting stars and planets has been investigated theoretically by several authors (Kornet et al. 2006; Kennedy & Kenyon 2008; Raymond et al. 2007).”

“Raymond et al. (2007) have simulated the formation of terrestrial planets, and find that habitable planets of & 0.3 M⊕ (the boundary for plate tectonics and atmospheric retention) are much less likely for M-dwarfs than G/K stars.”

“Figure 6 of Raymond et al. (2007) gives the fraction of simulations, P ( M ), for which stars of a given mass produce one or more HZ planets of critical mass (cid:4) 0.3 M (cid:1) as a function of M for 0.2 M (cid”

“However, large-scale mixing between zones does not happen until about 20 Myr, when the feeding zones of all three final planets overlap and encompass the entire terrestrial zone, out to ∼4 AU (Raymond et al.2007a).”

“The lower mass limit for planetary habitability is thought to be around 0.3 M ⊕ ( Raymond et al. 2007 ) , which corresponds to an estimated radius of 0.72 R ⊕ ( Zink & Hansen 2019, based on the empirical mass–radius relationship by Chen & Kipping 2017 ) .”

“…& Valenti 2005; Petigura et al. 2018; Teske et al. 2019), (ii) the planetary formation in different environments (Nayakshin 2017; Brasser & Mojzsis 2020), and (iii) the fraction of stars with exoplanets in our Galaxy (e.g., Raymond et al. 2007; Dressing & Charbonneau 2013, 2015; Hsu et al. 2019).”

“Understanding the dynamics of multi-planet systems around M dwarfs provides an important clue to planet formation around these low-mass stars (Lissauer 2007; Raymond et al. 2007; Zhu et al. 2012; Anglada-Escudé et al. 2013; Coleman et al. 2017; Morales et al. 2019).”

“…to successfully reproduce the broader characteristics of observed M-dwarf systems by numerically modeling in situ planetesimal accretion in a gas free environment around a small star (Raymond et al. 2007; Hoshino & Kokubo 2022), including the T1 system (Coleman et al. 2019; Clement et al. 2024).”

“…to argue in favor of one particular evolutionary pathway (pebble formation in the outer disk and subsequent inward migration: Ogihara & Ida 2009; Ormel et al. 2017; Coleman et al. 2019) over another (in-situ via plan-etesimal accretion: Raymond et al. 2007; Hansen 2015; Hoshino & Kokubo 2023).”

“If 26Al is present, a high fraction of water is mobilised and removed from ice-rich planetesimals and mainly dry planets result in the habitable zone [14].”

“Larger planets might best be able to generate their own protective magnetic fields, but simulations by Raymond et al. (2007) found that it could be difficult to form planets with > 0.3 Earth masses (Me) around stars smaller than 0.5 - 0.8 solar masses (Ms).”

“Through dynamical simulations of terrestrial planet formation from planetary embryos, Raymond et al. (2007) found that the masses of planets located inside the habitable zone decrease while the mass of the host star decreases.”

“Ces processus ont été étudiés pour des systèmes orbitant des étoiles du type du soleil (Raymond et al., 2007) et aussi pour des étoiles de faible masse (Ogihara and Ida, 2009).”

“From a theoretical perspective, stars in the habitable zone of low-mass stars are in danger of losing their atmospheres and surface water ( J. J. Lissauer 2007; S. N. Raymond et al. 2007 ) .”

“…from those of the terrestrial solar system planets, particularly because giant planets are often absent in such systems and volatile-rich formation channels may dominate ( S. N. Raymond et al. 2007; G. D. Mulders et al. 2015; S. R. Kane & R. A. Wittenmyer 2024; S. R. Kane & E. L. Miles 2025 ) .”

“5 M ⊕ (Raymond et al., 2007) might su ffi ce in this context instead of the 1 .”

“Whilst it is thought that planets below 0.3 M ⊕ cannot support atmospheric growth or plate tectonics on timescales required to harbor life (Raymond et al. 2007), it may be possible that moons of gas giants can reach earth size or larger (Teachey & Kipping 2018).”

“Other models scale the protoplanetary disk of an M-dwarf with the one of a Sun-like star, resulting in the formation of small and dry planets (Raymond et al., 2007).”