Planet Formation From Dust to Planetesimals Coagulation of dust grains forms millimeter- and centimeter-sized objects e m i t g n i p p o t S (Dominik and Tielens, 1997) Physical Characteristics MAGIC Drag forces Collisional coalescence of cm-sized particles Strong -> Week results in the formation of larger objects and Chemical binding Strong -> Week eventually planetesimals (km-sized). Surface gravity Week -> Strong Formation of Terrestrial Planets Planetary embryos are formed in ~10,000 y, separated by a few Runaway Growth mutual Hill radii. Gravitational interaction causes collisions among Accretion of embryos is a planetesimals and results in local process. the formation of Mercury- to Mars-sized objects (planetary embryo) Ida and Makino (1993) Kokubo and Ida (1995, 1996, 1998) 1 Final Stage What if the embryos existed also in the asteroid belt? Giant impacts among high velocity embryos that result in terrestrial planets in ~100 million years. What if the embryos existed also in the asteroid belt? Water & Earth - Current location of Earth too close to the Sun to retain water -The icy bodies appear at distances of 4.0 AU and larger -Earth must have acquired its water from larger distances The variation of relative water content with distance from the Sun implies that ASTEROIDS (2.5-4.2 AU) OR COMETS (> 30 AU)? water should have been accreted from distant material. D/H (x 10-6) Halley 260-350 Courtesy of F. Robert Hyakutake 280-300 Hale Bopp 250-410 The D/H ratio of Earth’s water rules out a dominant contribution of comets and suggests an asteroidal origin Numerical integrations also show that comets could have contributed at most 10% of the current water on Earth 2 WATER FROM ASTEROIDS Water Delivery According to asteroid • Earth is dry, ~0.05% H2O by mass. belt sculpting scenario, • Cometary late veneer: D/H too high? only 0.1% of the “primitive” asteroids • Giant wet asteroid(s) would have been • Disk snowstorms! (Kuchner, Youdin & Bate) accreted by the Earth. - Snowfall: 1”/day for 104 years Assuming 1 Earth mass of material and 10% water content this amounts to only 20% of the water currently on Images: Earth. Moreover it •Earth, arrived “early” in the • water world (Liss or Earth formation history Gibson • comets, ast belt Formation of Outer Planets - Gas-giants: Jupiter and Saturn i) Mostly gas (thick gaseous envelop) ii) Large rocky cores - Ice-giants: Uranus and Neptune JUPITER Need to form at a region where ice is available Outer planets must have formed at a region where gas and icy solid material stay abundant for the duration of their formation Disk Lifetime & Location of Snow Line Core-Accretion Model WATER FROM EMBRYOS (Gas-giant Planets) (Pollack et al. 1996) • Farther out in the protoplanetary disk where the temperature of the gas is lower, the density of solids is enhanced with rocky and icy planetesimals. • Such an enhancement of the solid density may cause collisional accumulation of solids and results in runaway growth to a mass of approximately10 Earth-masses in 0.5-1 million years. • These bodies may accrete gas (equivalent to 100 Earth-masses) from the disk within approximately 6-10 million years and form gas-giant planets. • The gas collapses and forms a thick envelope. Raymond et al., 2004 3 Stochasticity in the resulting water budget A large eccentric Jupiter inhibits the delivery of water to the inner S.S. Raymond et al., 2004 Chambers, 2001; Raymond et al., 2004 170 Etxrasolar Planets • explains the accretion of a LARGE amount of water -Close-in gaint planets (hot Jupiters) • The accreted water has the D/H ratio similar to that of carbonaceous chondritic origin -Eccentric orbits • The water accretion occurs DURING the formation of the Earth, NOT in a late veneer phase, in agreement with -Multi-planet systems geochemical modeling • The accretion of the water is a stochastic event, and therefore -Planets & binary stars explains why not all terrestrial planets had an identical primitive water budget (e.g.Mars) Planetary System Observations imply planets in binaries vs Binary Star System Circumbinary Disk Debris Disk GG Tau (a = 35 AU) HD 141569 Until a few years ago, it was Md = 0.2 Solar-mass separation ~950 AU generally believed that the collapse of a molecular cloud would result in the formation of a planetary system around a single star, or the formation of a dual-star system with no planets. Krist et al. 2005 Clampin et al. 2003 4 • Approximately 20% of extrasolar planets are in binary or multi-star systems • Almost all these binaries are wide (250-6500 AU) • γ Cephei (~ 18.5 AU), GJ 86 (~20 AU), and HD188753 (~12 AU) are binary or multi-star systems with at least one Jupiter-like planet Binary and multi-star systems with planets (Haghighipour, 2005) 6H6H6H6H HD142 (GJ 9002) HD3651HD9826 (Upsilon$K HD13445 (GJ 86) HD19994HD22049 (Epsilon(P HD27442 HD40979 HD41004 HD75732 (55 Cnc) HD80606 HD89744 HD114762 HD 117176 (70 Vir)HD120136 (Tau% HD121504 HD137759HD143761 (Rho&I HD178911 HD186472 (16 Cyg) HD190360 (GJ 777 A) HD192263 HD195019 HD213240 HD217107 HD219449 HD219542 HD222404 (Gamma&LOLP HD178911 PSR B1257-20 PSR B1620-26 γ Cephei 0.37-0.75 solar-mass 1.59 solar-mass υ Andromedae 1.7 Jupiter-mass http://mcdonaldobservatory.org/news/releases/2002/1009.html Triple-star system HD 188753 Giant Planet Formation (Konacki, 2005) 0.96 M Current theories of planet formation can explain Sun formation of planets around single stars Primary Core Accretion 1.06 MSun 0.67 MSun Porb = 156 days a = 0.67 AU Planet=1.14 Jupiter-mass Period=3.35 days Porb = 25.7 years, a = 12.3 AU, e = 0.50 5 Stellar Companion Affects the Structure of the Nebula Stellar Companion Affects the Structure of the Nebula A stellar companion affects the disk by truncating it to -Equal Mass Binary System -Single Solar Mass Star -Stars = Solar Mass 0.5-0.1 times the semimajor axis of the binary -No stellar companion -Binary Semimajor Axis = 50 AU -20 AU radius -Binary Eccentricity = 0.5 Boss (2005) (Artymowicz and Lubow, 1994) Stellar Companion Affects the γ Cephei Dynamics of Planetesimals -Increasing eccentricity -Increasing mutual collisions 0.37-0.75 solar-mass -Increasing the possibility of 1.59 solar-mass coalescence/ejection Thiebault et al (2004) 1.7 Jupiter-mass http://mcdonaldobservatory.org/news/releases/2002/1009.html Planet=Black, Binary=Red Long-Term Stability Orbital Stability Orbital Parameters of γ Cephei Semimajor Axis = 18.5 ± 1.1 AU Semimajor Axis = 20.3 ± 0.7 AU Orbit of the Jupiter-size planet is Eccentricity = 0.361 ± 0.023 Eccentricity = 0.389 ± 0.170 Hatzes et al (2003) Griffin et al (2002) stable for all values of - binary eccentricity ≤ 0.45 Numerical Simulation - planet orbital inclination ≤ 60 deg Binary semimajor eccentricity: 0.2 to 0.65 in steps of 0.05 Planet orbital inclination: 0 to 80 deg Secondary mass: 0.3 to 0.92 solar-mass (Haghighipour, 2005) 6 Habitable Zone γ Cephei A Jupiter-like planet in a binary star system A habitable zone is a region where an Earth-like planet receives the same amount of radiation as Earth receives from Binary the Sun, and it develops similar habitable conditions as those Period = 20750.6579 ± 1568.6 days on the Earth. For a star with luminosity L(R,T), this implies Semimajor Axis = 18.5 ± 1.1 AU Eccentricity = 0.361 ± 0.023 4 2 −2 ⎛ T ⎞ ⎛ R ⎞ ⎛ r ⎞ F(r) = ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ FSun ()rEarth Primary Secondary ⎝ T ⎠ ⎝ R ⎠ ⎝ r ⎠ where Sun Sun Earth Mass = 1.59 Solar-masses Mass = 0.35-0.75 Solar-masses Radius = 4.66 Solar-radii Radius = 0.5 Solar-radii 1 −2 4 2 −2 F(r) = L(R,T) r = σ T R r = Star’s brightness Temp = 4900 K Temp = 3500 K 4π Distance = 45 light years T = Star’s surface temperature Age = 3 billion years Planet R = Star’s radius Period = 905.574 ± 3.08 days r = Radial distance of habitable region from central star Semimajor Axis = 2.13 ± 0.05 AU Eccentricity = 0.12 ± 0.05 Min Mass = 1.7 Jupiter-masses Surface Temperature of primary T = 4900 K Habitability Radius of primary R = 4.66 Solar-radii The habitable zone of the primary of γ Cephei is UNSTABLE Habitable zone of γ Cephei : 3.1 AU < r < 3.7 AU (Haghighipour, 2006) Habitable Zone 2.13 AU 18.5 AU 1 AU 1.67 Jupiter Mass Primary Secondary Region of Stability of a Terrestrial Planet Habitable Zone a = 20, 30, 40 AU 2.13 AU 16,17,18 AU e = 0.0, 0.2, 0.4 0.5 AU 1 AU 4 AU Stellar Companion 0.8 AU Jupiter 0.3 AU 7 Numerical Simulations Companion = 1 Solar-mass, Semimajor Axis = 20 AU, Eccentricity = 0 (Haghighipour & Raymond 2006) - Binary separation = 20, 30, 40 AU - Binary eccentricity = 0.0, 0.2, 0.4 - 120 Embryos randomly distributed from 0.5 to 4 AU - Mass of embryos = 0.01 to 0.1 Earth-mass - Total mass of the disk = 4 Earth-masses - Jupiter at 5 AU - Stochastic => 3 different run for each case 1 Companion = 1 Solar-mass, Semimajor Axis = 30 AU, Eccentricity = 0 (Haghighipour & Raymond 2006) 2 Companion = 1 Solar-mass, Semimajor Axis = 20 AU, Eccentricity = 0.2 (Haghighipour & Raymond 2006) 2 8 I) The key factor in the amount of water delivered is Jupiter's eccentricity II) Dynamics of Jupiter is affected by the eccentric orbit of the stellar companion III) It would be important to understand where giant planets will form in binary systems and to explore whether there is a systematic relation between the binary parameters and the orbit of the outermost giant planet? Studies of crater densities at sites of known ages (from Apollo Evidence for HB ~4.0-3.8 Gy ago samples) give flux data back to ~3.8 Gy ago, and show that the bombardment was ~100 times higher - The ages of the rocks collected on the Moon ~3.9-3.8 Gy -The ages of many basins (impact features > 200km) ~3.9-3.8 Gy (Wilhelms, 1987; Ryder, 1994) Cataclysmic LHB (Tera, Ryder, Kring, Cohen, Koeberl..) Suggests a sudden and short-lived cratering episode ~ 3.9 Gy ago, Slowly fading LHB (Tera et al.