Origins of Gas Giant Planets

Transcription

1 Origins of Gas Giant Planets Ruth Murray-Clay Harvard-Smithsonian Center for Astrophysics Image Credit: NASA

2 Graduate Students Piso Tripathi Dawson Undergraduates Wolff Lau Alpert Mukherjee Wolansky Jackson

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7 HR 8799: A testbed for planet formation theories Neptune s orbital distance Marois et al. 2010

8 NASA, ESA, M. Robberto, HST Orion Treasury Project, L. Ricci

9 Alves, Lada, & Lada 2001

10 Alves, Lada, & Lada 2001

11 Alves, Lada, & Lada 2001

12 gas + dust + ice gas + dust

13 Test case HR 8799: Brown Dwarfs or Planets? M p /M * ~stars ~brown dwarfs 10 3 Jupiter ~planets 10 4 Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu Saturn r p (AU)

14 Test case HR 8799: Brown Dwarfs or Planets? M p /M * ~stars ~brown dwarfs Planetary companions Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu Jupiter Saturn r p (AU) ~planets

15 Test case HR 8799: Brown Dwarfs or Planets? Brown dwarf companions M p /M * ~stars ~brown dwarfs Planetary companions Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu Jupiter Saturn r p (AU) ~planets

16 Test case HR 8799: Brown Dwarfs or Planets? Brown dwarf companions M p /M * ~stars ~brown dwarfs Planetary companions Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu Jupiter Saturn r p (AU) ~planets Larger than most protoplanetary disks

17 Test case HR 8799: Brown Dwarfs or Planets? M p /M * Planetary companions Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu r p (AU) Brown dwarf companions HR 8799 Jupiter Saturn ~stars ~brown dwarfs ~planets Larger than most protoplanetary disks

18 Three ways to form companions turbulent fragmentation gravitational instability core accretion

19 Three ways to form companions HR 8799 turbulent fragmentation gravitational instability core accretion

20 Today s Goal: A framework for identifying giant planet formation processes. using HR 8799 as a test case Marois et al. 2010

21 Outline: ~70 AU Origin Stories ~ in situ formation by gravitational instability ~ in situ formation by core accretion Formation closer to star + scattering outward More complicated hybrid scenarios e.g., form a core close to the star, scatter outward, then accrete gas

22 Outline: ~70 AU Origin Stories ~ in situ formation by gravitational instability ~ in situ formation by core accretion Formation closer to star + scattering outward More complicated hybrid scenarios e.g., form a core close to the star, scatter outward, then accrete gas

23 Gravitational instability L self-gravity overcomes pressure and Keplerian shear most unstable scale: L H 3 M M frag (2 H) 2 4 H a

24 Gravitational Instability? Planets cannot grow after fragmentation and they must migrate in 100 minimum fragment distance Mass (MJup) 10 e minimum fragment mass Radius (AU) Kratter, Murray-Clay, & Youdin, ApJ 2010

25 Gravitational Instability? Planets cannot grow after fragmentation and they must migrate in 100 minimum fragment distance Mass (MJup) 10 e minimum fragment mass Stability requires resonance, suggesting migration Fabrycky & Murray-Clay Radius (AU) Kratter, Murray-Clay, & Youdin, ApJ 2010

26 Collapse must occur at the end of infall or the fragment will grow into a binary star Ṁ Ṁ disk

27 Collapse must occur at the end of infall or the fragment will grow into a binary star Ṁ Ṁ disk

28 Collapse must occur at the end of infall or the fragment will grow into a binary star Ṁ Ṁ disk

29 Collapse must occur at the end of infall or the fragment will grow into a binary star Ṁ Ṁ disk isolation mass is stellar!

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39 Gravitational instability planets can only be failed binary stars 10 0 ~stars M p /M * Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu HR 8799 expect higher mass companions from disk collapse r p (AU) ~brown dwarfs ~planets Larger than most protoplanetary disks

40 Outline: ~70 AU Origin Stories ~ in situ formation by gravitational instability ~ in situ formation by core accretion Formation closer to star + scattering outward More complicated hybrid scenarios e.g., form a core close to the star, scatter outward, then accrete gas

41 Core accretion: Need to grow a solid core through collisions

42 Growth timescale is set by: A: cross-section for collisions v: relative velocities of colliding bodies n: density of bodies available to accrete v t Volume = Avt A number density = n v H ~ v torb Sun # collisions in time t ~ n Avt ~ (nh) A (t/torb)

43 mass of object trying to grow orbital time: longer farther from the star t grow = Ṁ M M A t orb disk surface density in solids cross-section for collisions

44 mass of object trying to grow orbital time: longer farther from the star t grow = Ṁ M M A t orb disk surface density in solids cross-section for collisions

45 Cross-section regimes: physical cross-section gravitational focusing capture by gas drag into planetary atmosphere?

46 Let s make gas useful larger planetesimal or core Sun planetesimal

47 Gas Alters the Orbits of Single Planetesimals planetesimal wants to orbit The resulting F D m star at v Kep drag acceleration is small large radial pressure gradient but gas orbits more slowly v orb <v Kep v 2 orb r = GM r dp dr

48 In the absence of gas, satellites can orbit within the Hill radius RHill Sun

49 In the absence of gas, satellites can orbit within the Hill radius RHill Sun planetary gravity

50 In the absence of gas, satellites can orbit within the Hill radius RHill Sun planetary gravity

51 In the absence of gas, satellites can orbit within the Hill radius RHill Sun planetary gravity

52 In the absence of gas, satellites can orbit within the Hill radius RHill tidal acceleration Sun planetary gravity

53 In the absence of gas, satellites can orbit within the Hill radius RHill tidal acceleration Sun planetary gravity

54 Wind Shearing (WISH) No gas: Gas: planetesimal RHill RHill core RWISH Perets & Murray-Clay (2011)

55 A core + planetesimal in gas can: shear apart orbit around star mutual orbit or inspiral and merge

56 A core + planetesimal in gas can: shear apart orbit around star mutual orbit or inspiral and merge F D m F D m

57 Wind-Shearing Limits Orbital Stability Hill radius WISH radius large body radius core radius R stab /r b AU r b = 10km R H /r b Epstein Ram Pressure Drag 1 < Re < 800 Stokes R WS /r b r b /r b 10km r s r b = core radius Ram binary stability r s (cm) small body radius (cm) Perets & Murray-Clay (2011)

58 A core + planetesimal in gas can: shear apart orbit around star mutual orbit or inspiral and merge F D m F D m

59 τmerge (yr) 10 merge (yr) time toτ merge (yr) Epstein 1010 ~Pluto radius 40 AU 1 AU 8 typical disk lifetime Stokes: 2 τmerge rs ~km 8 Stokes: 2 τmerge rs 104 Porb AU 106 Ram: τmerge rs Porb 0 Epstein Stokes Porb Porb Porb Epstein: τmerge rs 100 Stokes 10 (yr) 104 Stokes For Small Planetesimals, Merger Times <10Disk Lifetimes 4 τmerge (yr) τmerge (yr) Ram Ram AU rs (cm) Epstein: τmerge rs rs (cm) small body radius (cm) Ram Perets & Murray-Clay (2011)

60 Binary Capture RHill dissipation due to interaction with gas RWISH Murray-Clay & Perets (in prep) (see also Ormel & Klahr 2010)

61 Integration of forces confirms that capture can happen with a cross-section as large as the Hill radius 0.02 y (AU) RHill Ratm x (AU)

62 RHill Ratm Capture by the atmosphere is only possible if the small particle RWISH can decouple from the exterior gas.

63 Integrations confirm that well-entrained particles can be swept around the core, preventing accretion 0.02 y (AU) RHill Ratm RWISH x (AU)

64 Growth times at 70 AU can be short enough to nucleate an atmosphere Mcore (MEarth) time (yr) M crit (Rafikov 2006,2010) 50% of MMSN solids in equal mass per log bin from mm to 10cm Murray-Clay et al. (in prep.)

65 Growth times at 70 AU can be short enough to nucleate an atmosphere Mcore (MEarth) time (yr) M crit (Rafikov 2006,2010) 50% of MMSN solids in equal mass per log bin from mm to 10cm Murray-Clay et al. (in prep.)

66 Turbulence doesn t prevent the final stage of core growth by capture of planetesimals 0.02 y (AU) RHill Ratm x (AU) =0.01

67 HR 8799: Brown Dwarfs or Planets? 10 0 ~stars M p /M * HR 8799 ~brown dwarfs ~planets 10 4 Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu r p (AU) Larger than most protoplanetary disks

68 HR 8799: Brown Dwarfs or Planets? 10 0 ~stars M p /M * HR 8799 ~brown dwarfs ~planets 10 4 Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu r p (AU) Larger than most protoplanetary disks

69 HR 8799: Brown Dwarfs or Planets? 10 0 ~stars M p /M * HR 8799 ~brown dwarfs ~planets 10 4 Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu r p (AU) Larger than most protoplanetary disks

70 10 0 Gemini Planet Imager (PI: Bruce Macintosh) ~stars M p /M * HR 8799 ~brown dwarfs ~planets 10 4 Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu r p (AU) Larger than most protoplanetary disks

71 Overlapping populations will have different mass distributions M p /M * r p (AU)

72 Overlapping populations will have different mass distributions M p /M * r p (AU)

73 Overlapping populations will have different mass distributions M p /M * r p (AU)

74 Overlapping populations will have different mass distributions Excluding radial orbits: Number M p /M * 10 2 Mass r p (AU) Number Mass Stellar metallicity and planetary atmospheric composition provide additional discriminants

75 CO snowline ~40 AU C and O frozen out together H2O snowline ~2 AU C rich gas O rich solids C Oberg, Murray-Clay, & Bergin, ApJL (2011) O

76 Outline: ~70 AU Origin Stories ~ in situ formation by gravitational instability ~ in situ formation by core accretion Formation closer to star + scattering outward More complicated hybrid scenarios e.g., form a core close to the star, scatter outward, then accrete gas

77 Metal-rich stars host more moved planets: A signature of planet-planet interactions planets{ moved hot Jupiters highly eccentric planets ~ in situ formation? Dawson & Murray-Clay 2013

78 Test case HR 8799: Brown Dwarfs or Planets? 10 0 GPI ~stars M p /M * HR 8799 ~brown dwarfs Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu Jupiter Saturn r p (AU) ~planets Larger than most protoplanetary disks

79 Test case HR 8799: Brown Dwarfs or Planets? 10 0 GPI ~stars M p /M * HR 8799 ~brown dwarfs Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu Jupiter Saturn r p (AU) gravitational instability ~planets Larger than most protoplanetary disks

80 Test case HR 8799: Brown Dwarfs or Planets? 10 0 GPI ~stars M p /M * HR 8799 ~brown dwarfs Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu Jupiter Saturn r p (AU) core accretion ~planets Larger than most protoplanetary disks

81 How do giant planets and brown dwarfs form? M p /M * core accretion disk gravitational instability? Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu HR 8799: signpost Jupiter Saturn r p (AU) turbulent fragmentation ~stars ~brown dwarfs ~planets Larger than most protoplanetary disks

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83 Formation and evolution of planetary systems around stars with different masses, at different stages of evolution, and in different environments. Infall and disk accretion sets the initial conditions for growth of planetesimals and planets Piso, Youdin, & Murray-Clay (final stages) Wolansky (senior thesis) Mukherjee Graduate Students Undergraduates which then migrate as they interact with other planets, residual gas and planetesimals Wolff, Dawson, & Murray-Clay (2012) Dawson & Murray-Clay (2012) Dawson, Murray-Clay, & Fabrycky (2011) Lau & Murray-Clay (final stages) Jackson (junior project) and then evolve dynamically over long timescales all the while developing atmospheres that depend on this history. Tripathi Dawson, Murray-Clay, & Johnson (submitted) Dawson et al. (2012) Dawson & Murray-Clay (2013) Alpert

84 How do giant planets and brown dwarfs form? M p /M * core accretion disk gravitational instability? Kratter, Murray-Clay, & Youdin, ApJ (2010) Data: Zuckerman & Song 2009; exoplanet.eu HR 8799: signpost Jupiter Saturn r p (AU) turbulent fragmentation ~stars ~brown dwarfs ~planets Larger than most protoplanetary disks