Statistics – Computation
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p11a1586d&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P11A-1586
Statistics
Computation
[1027] Geochemistry / Composition Of The Planets, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution
Scientific paper
The late stages of planetary accretion involve stochastic, large collisions [1]. Although such collisions are usually assumed to result in perfect mergers, many of the collisions may instead result in hit-and-run events [2, 3] or erosion of existing bodies' mantles [4]. Impact-related erosion can have profound consequences for the rate and style of accretion [5] and the bulk chemistries of terrestrial planets [6]. Here we present some preliminary investigations into the occurrence of erosional collisions during late-stage accretion and consequences for the bulk chemistry and isotopic characteristics of the resulting planets.
We have performed a preliminary investigation into the nature of late-stage accretion using an N-body simulation in which the different possible collision outcomes are treated in a more realistic manner than hitherto. The simulation starts with 155 planetesimals of roughly lunar mass; at the end, four bodies remain with masses of 0.83, 0.62, 0.33, and 0.02 Mearth.
Collisional efficiency is parametrized based on the results of [7]. The results of the collisions, especially highly disruptive collisions, are idealized in order to be computationally tractable; in particular, bodies smaller than a minimum mass are not permitted.
To track the bulk compositional evolution of the bodies, we assume all are initially chondritic. We alter the bulk chemistry after an impact according to a scheme which is based on the assumption that mantle material is much more likely to be eroded than core material.
We track the tungsten isotopic evolution of each body using the method of [8] and treat the extent of core-mantle equilibration as a free parameter. The stochastic nature of planetary accretion means that even with perfect mergers, the tungsten isotope anomaly (eW) of the final bodies will vary, due to variations in the timing of the impacts which create the final bodies. Irrespective of accretion style, the extent of core re-equilibration affects eW.
Including the effects of impact erosion results in a larger spread in eW and an increase in the average eW. A range in values of silicate mass fraction is produced, supporting the idea that erosional accretion can cause changes in bulk chemistry [6].
Compared with simulations assuming perfect mergers, we find that the time required to complete terrestrial planet formation is longer (190 Myr). Due to the long formation time and the observed existence of tungsten isotopic anomalies preserved in terrestrial and meteoric samples, core-mantle equilibration was likely minor.
Future work will include a more realistic model for fragment size distribution and a greater number of simulation runs. [1] O'Brien et al. (2006) Icarus 184, 39-58. [2] Asphaug et al. (2006) Nature 439, 155-160. [3] Kokubo & Genda (2010) ApJ 714, L21-L25. [4] Benz et al. (2007) Space Sci Rev 132, 189-202. [5] Chambers (2008) Icarus 198, 256-273. [6] O'Neill & Palme (2008) Phil Trans R Soc A 366, 4205-4238. [7] Asphaug (2009) Ann Rev Earth Planet Sci 37, 413-448. [8] Nimmo & Agnor (2006) EPSL 243, 26-43. [9] Agnor & Asphaug (2004) ApJ 613, L157-L160. [10] Kleine et al. (2009) GCA 75, 5150-5188.
Asphaug Erik Ian
Chambers John
Dwyer C. A.
Nimmo Francis
O'Brien David Patrick
No associations
LandOfFree
Erosion during accretion: Consequences for planetary iron-silicate ratios and tungsten isotope anomalies does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Erosion during accretion: Consequences for planetary iron-silicate ratios and tungsten isotope anomalies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Erosion during accretion: Consequences for planetary iron-silicate ratios and tungsten isotope anomalies will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-867444