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(2020) A New Isotopic Perspective on the Solar System’s Stardust Inventory

Leitner J, Hoppe P & Kodolányi J


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01g: Room 1, Tuesday 23rd June 08:00 - 08:03

Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.

Submitted by Mattias Ek on Monday 22nd June 13:21
Hi Jan. You show that some of the group 1 & 2 silicates were likley SN in orgin and that this means the SN dust makes up a larger fraction of stardust than previously thought. Can you quantify roughly what fraction of stardust might actually have a SN origin?
Hi Mattias. The estimate has to be quite "rough", since we do not have a lot of high-precision Mg isotope data until now. In the current state, my best guess is that ~10 % (give or take a few) of the group 1 silicates might actually come from SNe instead (for the group 2 grains, statistics is even worse, and a high-mass AGB star origin is also quite likely when they are enriched in 25Mg). However, this estimate might well change when we accumulate more data.

Submitted by Mattias Ek on Monday 22nd June 13:37
Is the 44Ti/48Ti initial you used for the Pignatari 25T-H model constrained in any way?
The number for the 44Ti/48Ti initial that I gave in the plot is based on my grain fitting calculations; i.e., with this ratio, I can reproduce the Mg-, Si- and Ca-isotopic compositions of the two grains in question with 25T-H model data.

Submitted by Nan Liu on Monday 22nd June 16:56
Could the detected 44Ca excesses be explained by neutron-capture instead of the initial presence of 44Ti in supernovae, e.g., the neutron-burst process in the He/C zone?
Hi Nan, I think this is rather unlikely for the two grains in question. First of all, I would also expect positive 42Ca/40Ca-anomalies in the grains if this was the case - which we don't see. And second, the Mg- and Si-isotopic ratios of the grains can be fitted quite well with Marcos 25T-H model (due to the O/nova-zone), but cannot be modeled based on the "standard" Rauscher or WW07-SN models. Moreover, in a neutron-rich environment, you would also have high 26Mg-enrichments accompanying the 25Mg-excesses, which is also not observed.

Submitted by Larry Nittler on Monday 22nd June 20:25
Nice presentation, Jan. Sorry I can't be up at 3 am for the live Q&A. Glad to see the Ca data - did you estimate the Ca contents of the grains and were they different from non-25Mg rich grains?
Hi Larry, thank you. The four grains I measured have Ca/Mg-ratios from 0.013 to 0.66 (three grains between 0.15 and 0.66) - errors typically dominated by the sensitivity factors. Peter determined Ca/Mg for six ("GCE-type") grains from our ApJ paper from 2018, with ratios between 0.005 and 0.33 (five out of six <0.04). So, statistics is very limited... but there might be a trend towards higher Ca/Mg for the 25Mg-rich grains (although this needs to be confirmed by more data).

Submitted by Sasha Krot on Tuesday 23rd June 03:03
Nice talk, Jan. It is interesting that some CAIs recorded variations in the initial Mg-isotope compositions, either 26Mg deficit or 25Mg excess (see Larsen et al., 2020, EPSL, 535)
Thank you, Sasha. That is interesting indeed, I will definitely look into this - thanks for the reference!

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