SLIDE 1
Changing the growing Earth’s composition via collisions
Phil Carter
University of Bristol
The problem with the Earth
Formed from the same material ?
Bonsor, Leinhardt et al. 2015 Data from Palme & O’neill (2003)
Changing the growing Earths composition via collisions Phil Carter - - PowerPoint PPT Presentation
Changing the growing Earths composition via collisions Phil Carter - - PowerPoint PPT Presentation
Changing the growing Earths composition via collisions Phil Carter University of Bristol Zo M Leinhardt Tim Elliot Michael J Walter Sarah T Stewart Amy Bonsor Exoplanets in Lund - 7th May 2015 The problem with the Earth Formed from
SLIDE 2
SLIDE 3
The problem with the Earth
Boyet & Carlson 2006 Boyet & Carlson 2005
- Hidden reservoir
- Inhomogeneous
nebula
- Collisions
Superchondritic
142Nd/144Nd
SLIDE 4
Simulate accreting Earth
- PKDGRAV - N body code
- EDACM - Empirically Derived Analytical Collision Model
(Leinhardt & Stewart 2011; Leinhardt et al. 2015)
- 100 000 planetesimals, most ~200 km radius
- Particle radii inflated by factor f=6 to speed
up evolution Run for 600 000 yr, effective time ~20 Myr
Marcus et al. 2010 GADGET SPH
- Mantle stripping law (Marcus et al. 2010)
- favours accretion of core material
by largest remnants
SLIDE 5
Core vs mantle with EDACM
Perfect merging Partial accretion Hit and run
Projectile disrupted
Erosion or supercatastrophic disruption
SLIDE 6
Resolution limit
Collisions can produce debris, Resolved planetesimals reaccrete
- cycling of material through debris bins
Carter, Leinhardt et al. in prep
SLIDE 7
Growth of terrestrial embryos (no gas)
SLIDE 8
Growth of terrestrial embryos
Carter, Leinhardt et al. in prep
SLIDE 9
What does this mean for the bulk composition?
0.22 0.35
Bonsor, Leinhardt et al. 2015
SLIDE 10
What effect does gas drag have?
No gas Constant gas Decaying gas No gas Constant gas Decaying gas
Carter, Leinhardt et al. in prep
SLIDE 11
Conclusions
- A series of collisions can significantly alter the chemical composition
- f terrestrial planet embryos during runaway and oligarchic growth.
- Compositional changes work both ways. If the Earth represents
“core enhancement” other terrestrial planets should show “mantle enhancement”.
- Collisional accretion during the growth of terrestrial embryos may do
just enough to explain the non-chondritic nature of the Earth. The giant impact phase may further enhance the compositional changes.
- Gas drag reduces the degree of variation seen in the composition
after the oligarchic growth phase, but realistic gas discs that decay early in the growth of the Earth have only a small effect.