Amaya Moro-Martín Centro de Astrobiología (INTA-CSIC) & Princeton Univ.

1. Published in Belbruno, Moro-Martín, Malhotra, Savransky (Astrobiology 2012) Chaotic exchange of solid material between planetary systems: implications for lithopanspermia Amaya Moro-Martín Centro de Astrobiología (INTA-CSIC) & Princeton Univ. Collaborators: Edward Belbruno (Princeton Univ.), Renu Malhotra (Univ. of Arizona), Dmitry Savransky (Princeton Univ. and Lawrence Livermore National Laboratory)

2. Giant planets are common Approx. 20% of stars harbor giant planets < 20 AU

3. How common are they? • The dust is not primordial but it must be generated by planetesimals • But there is evidence of dust around older stars (debris disks). Planetesimal formation takes places under a wide range of conditions (Kennedy in prep.) • Protoplanetary disks of gas and dust (100:1 mass ratio) are present around most stars; they dissipate in ~ 6 Myr. - A (26%), F (24%), G (19%), K (9.5%), M (1.3%) dust lifetime << stellar age - Also present around white dwarfs (Jura et al. 2006, 2007) 10 Myr-10,000 Myr 0.01-1 Myr Planetesimal disks are common

5. (Jewitt 2010)

6. Solar System debris disk

7. extra-solar debris disk β-Pictoris (Schultz, HST)

8. Giant planets eject planetesimals efficiently (Raymond, Armitage, Moro-Martin et al. 2011)

9. Giant planets are common • Planetesimal disks are common • Giant planets eject planetesimals efficiently The interstellar medium must be filled with planetesimals Is the exchange of solid material possible between planetary systems?

10. The Sun was born in an open star cluster Cluster properties (Adams 2010) (similar to Orion’s Trapezium) Solar System properties that depend on birth environment: - evidence of short-lived radionuclides in meteorites - dynamical properties of outer planets and Kuiper Belt - Number of stars: N = 4300 (N=1000-10000) - Cluster mass: M = <mstar> N = 3784 Msun - Cluster size: R ~1pc (N/300)0.5 = 3.78 pc - Average stellar distance: D = n-1/3 = 0.375 pc - Cluster lifetime: t = 2.3Myr M0.6 = 322.5 Myr (135-535 Myr for N=1000-10000) Transfer of solid material between single stars in an open star cluster

11. Minimum energy; maximizes transfer probability planetary system of destination (relative velocity between stars) (ejection velocity) • Typical ejection velocity ~ 0.1 km/s • Assume both planetary systems harbor a Jupiter-like planet weak stability boundary for capture (σ = 1 km/s) star giant planet • The transfer takes place between two weak stability boundaries: planetary fragment giant planet • Stars relative velocity ~ 1 km/s (determining capture velocity) weak stability boundary for escape (σ = 0.1 km/s) star planetary system of origin Weak transfer using quasi-parabolic orbits • Region where the particle is tenuously and temporarily captured. • Created by the gravitational fields of the central star, the giant planet and the rest stars in the cluster. • The particle slowly meanders between both planetary systems.

12. Monte Carlo simulations (Belbruno, Moro-Martín, Malhotra, Savransky, 2012)

13. Monte Carlo simulations (Belbruno, Moro-Martín, Malhotra, Savransky, 2012)

14. Weak capture probabilities Comparison to previous work • Melosh (2003): • - transfer between single stars in the solar local neighborhood (after cluster dispersal) • (ours: before cluster disperses) • - stars velocitiy dispersion: 20 km/s(ours: 1 km/s) • - hyperbolic trajectories with median ejection speed of 5 km/s (ours: 0.1 km/s) • - capture probability ~109 times smaller than with weak transfer • Adams & Spergel (2005) • - transfer between binary stars in an open cluster (ours: single stars like the Sun) • - hyperbolic trajectories with median ejection speed of 5 km/s (ours: 0.1 km/s) • - capture probability ~103 times smaller than with weak transfer

15. Number of bodies >10 kg may have been transferred Number of bodies > 10 kg Number of bodies >10 kg that populated the WSB Adopt a planetesimal size distribution Number of weak transfer events: O(1014)-O(1016) (from KBO observations and coagulation models) (adopting a MMSN) (using a capture probability of 0.15%) (using an Oort Cloud formation efficiency of 1%, Brasser et al. 2012). dN/dD ∝ D−q1 for D > D0 dN/dD ∝ D−q2 for D < D0 Dmax = 2000 km (Pluto) Dmin = 1 μm (blow-out size) Number of weak transfer events (between the Sun and its closest cluster neighbor)

16. Birth cluster lifetime, dispersed over approx. 135–535 million years Evidence of liquid water on Earth’s surface end of LHB Cooling of Earth’s crust Heavy bombardment; planetesimal clearing; population of the sun’s WSB with planetary fragments 1st evidence of microbiological activity 1st microfossils star cluster Moon formation 135 Myr 322 Myr 535 Myr solar system 700 Myr (Adams 2010) Earth t = 0 44 Myr 70 Myr 164 288 718 Myr 1170 Myr (shortly after end end of LHB) solar system (CAI) formation Myr Myr (Kleine et al. 2005) (Harrison et al. 2005) (Mojzsis et al. 2001) (Mojzsis et al. 1996) (Wilde et al. 2001). (Wacey et al. 2011) (Schopf, 1993) (4.57 Ga) window of opportunity of lithopanspermia from Earth Timeline

17. Assuming l (km) of the Earth surface was ejected, this correspond to a mass of... adopting a power-law size distribution, ~ 1% remained weakly shocked (allowing microorganisms to survive) ~ ~ 1% populated the Oort Cloud (WSB of the Solar System) ~ 5‧105 ‧ l(km) ~ 0.15% may have been transferred to the nearest solar-type stars ~ the number of bodies > 10 kg is How much material may have been ejected from Earth?

18. Time for ejection 4 Myr min. 50 Myr median. 6 Myr time of flight to Resc Time for transfer 5 Myr (at 0.1 km/s) Time for capture by terrestrial planet Survival of microorganisms could be viable via meteorites exceeding 1m in size 10’s Myr Comparison between transfer and life survival timescales Valtonen et al. (2009)

19. We study the transfer of meteoroids between two planetary systems embedded in an open star cluster. • If life on Earth had an early start (arising shortly after liquid water was available on the surface), life could have been transferred to other systems. • And vice versa, if life had a sufficiently early start in other planetary systems, it could have seeded the Earth (and may have survived the LHB). • We use chaotic, quasi-parabolic orbits of minimal energy that increase greatly the transfer probability. Orion’s Trapezium cluster (2.2 μm) In a nutshell • We find that significant quantities of solid material are exchanged.