Open problems in terrestrial planet formation：在类地行星形成的开放问题

1、Open problems in terrestrial planet formationSean RaymondLaboratoire dAstrophysique de Bordeauxwith audience contributions welcome!How did the Solar System form?Simulations can roughly reproduce the masses and orbits of Earth and Venus (OBrien et al 2006; Kenyon & Bromley 2006; Chambers 2001; Agnor

2、et al 1999; Raymond et al 2006)Biggest problem: Mars small size (Wetherill 1991)Accretion process strongly dependent on giant planets (Levison & Agnor 2003; Raymond et al 2004)Goal: Reproduce inner solar system Constrain Jup, Sats orbits at early timesTest relevant physicsConstraintsMasses, orbits o

3、f terrestrial planetsMars small mass is a mystery (Wetherill 1991, Chambers 2001)Very low eccentricities (OBrien et al 2006)Structure of asteroid beltSeparation of S, C typesNo evidence for remnant embryos (gaps)Accretion timescales from Hf/W, Sm/NdEarth/Moon: 50-150 Myr (Jacobsen 2005; Touboul et a

4、l 2007)Mars: 1-10 Myr (Nimmo & Kleine 2007)Water delivery to EarthAsteroidal source explains D/H (Morbidelli et al 2000)Other models exist (Ikoma & Genda 2007; Muralidharan et al 2021)Stronger ConstraintsDust (m) Planete-simals (km)Cores EmbryosEarth-sized planets104-5 yrs105-7 yrs107-8 yrsdust stic

5、kingGrav. collapse (cm - m)Runaway growthOligarchic growthGas giantsLate-stage accretionRunaway gas accretionInitial conditions for late-stage accretionPlanetary embryos (aka protoplanets) form by runaway and oligarchic growth: Moon-Mars sized (105-6 yrs) (Kokubo & Ida 1998, Leinhardt & Richardson 2

6、005)Late-stage accretion starts when local mass in embryos and planetesimals is comparable (Kenyon & Bromley 2006)Kokubo & Ida 2002EccentricitySemimajor Axis (AU)(Giant planets must form in few Myr, so they affect late stages)Key factors for accretion1. Giant Planets (Levison & Agnor 2003)Formation

7、models predict low eccentricityNice model: Jup, Sat closer than 2:1 MMR during accretion (Tsiganis et al 2005; Gomes et al 2005)Perhaps in chain of resonances (Morbidelli et al 2007)2. Disk Properties (Wetherill 1996, Raymond et al 2005)Total mass 5 Earth masses inside 4 AU (Weidenschilling 1977; Ha

8、yashi 1981) r-1.5 (MMSN) or perhaps more complex (Jin et al 2021; Desch 2007)Nice model 2 (J, S in 3:2 MMR)No Mars analogsEmbryos in asteroid beltInconsistent with observed structure if embryo Mars-mass or largerNice model 2 (J, S in 3:2 MMR)No Mars analogsEmbryos in asteroid beltInconsistent with o

9、bserved structure if embryo Mars-mass or largerNice model 2 (J, S in 3:2 MMR)Eccentric Jup, Sat (e0=0.1)Eccentric Jup, Sat (e00.1)Strong secular resonance (6) at 2.2 AUMars consistently forms in correct configurationEarth and Venus are dryInconsistent with Kuiper Belt structure no migration of giant

10、 planets possible (Malhotra 1995, Levison & Morbidelli 2003)Influence of giant planetsRaymond, OBrien, Morbidelli, & Kaib 2021Influence of giant planetsRaymond, OBrien, Morbidelli, & Kaib 2021Hard to form low-e, highly concentrated terrestrial planet systemsMarsSmall Mars forms naturally if inner di

11、sk is truncated at 1-1.5 AU (Agnor et al 1999; Hansen 2021)Can reproduce all 4 terrestrial planets if embryos only existed from 0.7-1 AU (Hansen 2021)Hansen 2021Other effectsGas disk effects:Type 1 migration (McNeil et al 2005; Morishima et al 2021)Secular resonance sweeping (Nagasawa et al 2005; Th

12、ommes et al 2021)Collisional fragmentation (Alexander & Agnor 1998; Kokubo, Genda)Morishima et al 2021Jin et al (2021) diskAssume MRI is effective in inner, outer disk but not in betweenAt boundary between low, high viscosity, get minimum in densityOccurs at 1.5 AUExplanation for Mars small mass?Jin

13、 et al (2021)SummaryNo tested configuration of Jup, Sat reproduces all constraints (Raymond et al 2021)Closest is eccentric Jup, Sat but Earth is dry and JS not consistent with Kuiper BeltIncluding gas disk effects doesnt solve the problem (Morishima et al 2021)Hard to reproduce Mars small sizeStron

14、g constraint on Jup, Sats orbits at early timesWas there just a narrow annulus of embryos? (Hansen 2021)Whats missing?Secular resonance sweeping during disk dispersal (Nagasawa et al 2005, Thommes et al 2021)Something else?Recent progressMorishima et al 2021, 2021Raymond, OBrien, Morbidelli, Kaib 20

15、21Hansen 2021Thommes, Nagasawa & Lin 2021OBrien, Morbidelli & Levison 2006Raymond, Quinn & Lunine 2006Kenyon & Bromley 2006Nagasawa, Thommes & Lin 2005Kominami & Ida 2002, 2004Chambers 2001Agnor, Canup & Levison 1999Initial conditionsStart of chaotic growth phase (Wetherill 1985; Kenyon & Bromley 2006)Equal mass in 1000-2000 planetesimals and 100 embryos (5 ME total)Embryos is Mars vicinity are 0.1-0.4 Mars massesIntegrate for 200 Myr + with Mercury (Chambers 1999)MarsLow-ecc.Ast. beltForm. timeEarth WaterCurrent JSEccentric JSNice model 1Nice 1 eccentricNice