Amaya Moro-Martín Centro de Astrobiología (INTA-CSIC) & Princeton Univ.
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Transcript of Amaya Moro-Martín Centro de Astrobiología (INTA-CSIC) & Princeton Univ.
Amaya Moro-MartínCentro de Astrobiología (INTA-CSIC) & Princeton Univ.
Chaotic exchange of solid material between planetary
systems: implications for lithopanspermia
Collaborators: Edward Belbruno (Princeton Univ.), Renu Malhotra (Univ. of Arizona), Dmitry Savransky (Princeton Univ. and Lawrence Livermore National Laboratory)
Published in Belbruno, Moro-Martín, Malhotra, Savransky (Astrobiology 2012)
How common are they?
- Also present around white dwarfs (Jura et al. 2006, 2007)
- A (26%), F (24%), G (19%), K (9.5%), M (1.3%) (Kennedy in prep.)
Planetesimal disks are common
0.01-1 Myr 10 Myr-10,000 Myrdust lifetime << stellar age
The dust is not primordial but it must be
generated by planetesimals
Planetesimal formation takes
places under a wide range of
conditions
•But there is evidence of dust around older stars (debris
disks).
•Protoplanetary disks of gas and dust (100:1 mass ratio)
are present around most stars; they dissipate in ~ 6 Myr.
Is the exchange of solid material
possible between planetary systems?
The interstellar medium must be filled with
planetesimals
• Giant planets are common
• Planetesimal disks are common
• Giant planets eject planetesimals
efficiently
Transfer of solid material between single stars in an open star cluster
Solar System properties that depend on birth environment: - evidence of short-lived radionuclides in meteorites - dynamical properties of outer planets and Kuiper Belt
The Sun was born in an open star cluster
- 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)
(similar to Orion’s Trapezium)
Cluster properties (Adams 2010)
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.
•The transfer takes place between two
weak stability boundaries: planetar
y fragme
nt
weak stability boundary for
capture (σ = 1 km/s)
weak stability boundary for
escape (σ = 0.1 km/s)
•Stars relative velocity ~ 1 km/s (determining capture velocity)
(relative velocity between
stars)
stargiant planet
giant plane
t
planetary system of destination
planetary system of origin
star
•Assume both planetary systems harbor a
Jupiter-like planet
(ejection velocity)•Typical ejection velocity ~ 0.1 km/s
•Minimum energy; maximizes transfer
probability
M* source (Msun) M* target (Msun) Capture probab.
1.0 1.0 0.15%
1.0 0.5 0.05%
0.5 1.0 0.12%
Weak capture probabilities
•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
Comparison to previous work
(between the Sun and its closest cluster neighbor)
Number of weak transfer events
(from KBO observations and coagulation models)
Dmax = 2000 km (Pluto) Dmin = 1 μm (blow-out size)
dN/dD ∝ D−q1 for D > D0
dN/dD ∝ D−q2 for D < D0
Adopt a planetesimal size distribution
(adopting a MMSN)
Number of bodies > 10
kg
(using an Oort Cloud formation efficiency of 1%, Brasser et al. 2012).
Number of bodies >10 kg
that populated the
WSB
(using a capture probability of 0.15%)
Number of bodies >10 kg
may have been
transferred
Number of weak transfer events: O(1014)-O(1016)
Timeline
window of opportunity of lithopanspermia from Earth
Birth cluster lifetime, dispersed over approx. 135–535 million years
star cluster135 Myr
535 Myr
(Adams 2010)
322 Myr
Moon formation
44 Myr
Cooling of Earth’s crust
70 Myr
1st microfossils
1170 Myr
t = 0
solar system (CAI)
formation
718 Myr
Earth
(4.57 Ga)
(Kleine et al. 2005)
(Mojzsis et al. 1996)
(Wacey et al. 2011)(Harrison et al. 2005) (Schopf, 1993)
(shortly after end end of LHB)
Evidence of liquid water on Earth’s
surface
164 288Myr Myr
(Wilde et al. 2001).
(Mojzsis et al. 2001)
1st evidence of microbiological
activity
solar system 700
Myr
end of LHB
Heavy bombardment; planetesimal clearing; population of the sun’s WSB
with planetary fragments
Assuming l (km) of the Earth surface was ejected, this correspond to a mass of...
adopting a power-law size distribution,
the number of bodies > 10 kg is
~ 1% remained weakly shocked (allowing microorganisms to survive) ~
How much material may have been ejected from Earth?
~ 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 ~
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 planet10’s Myr
Comparison between transfer and life survival timescales
Size Max. survival time
0-0.03 m 12-15 Myr
0.03-0.67 m 15-40 Myr
0.67-1 m 40-70 Myr
1-1.67 m 70-200 Myr
1.67-2 m 200-300 Myr
2-2.33 m 300-400 Myr
2.33-2.67 400-500 MyrValtonen et al. (2009)
Survival of microorganisms could be viable via meteorites exceeding 1m in size
In a nutshell
•We use chaotic, quasi-parabolic orbits of minimal energy that increase greatly the transfer probability.
•We study the transfer of meteoroids between two planetary systems embedded in an open star cluster.
Orion’s Trapezium cluster (2.2 μm)
•We find that significant quantities of solid material are exchanged.
•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).