Mankato for R. Palma to relocate to Centre de Recherches Pétrographiques et Géochimiques (CRPG) in Nancy, France for academic year 2016–17. Research at the University of Minnesota was supported throughout this project by NASA grants NNX08AG21G, NNX10AI88G, and NNX14AF23G from the Laboratory Analysis of Returned Samples (LARS) program. Research at UC Berkeley was supported by NASA grants NNX11AF12G and NNX16AI15G. E. Füri gratefully acknowledges support from Centre National d'Etudes Spatiales (CNES) through a postdoctoral fellowship and support from the European Research Council (grant no. 715028). Constructive reviews by D. Brownlee and a reviewer who wishes to remain anonymous were helpful in improving the manuscript.

*Editorial Handling*—Dr. Donald Brownlee

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# APPENDIX: SAMPLE PREPARATION SPECIFICS AND TABLE 1 SAMPLE IDENTIFIERS

## 1) CELL C2044 SAMPLES

(a) *Blank Wafer Samples:* Three 200 µm wafers (Fig. 2) were cut vertically from the end of the blank block furthest from T41. Thus, these wafers each had only a thin ~200 µm x ~5 mm space-exposed area. Two of the three wafers were subdivided as follows: samples C2044,18,41,0,0 (wafer 18) and C2044,20,41,0,0 (wafer 20) were each split into samples A and B to be analyzed individually: C2044,18A,41,0,0 (wafer 18A) had area 0.17 cm² and was located below C2044,18B,41,0,0, (wafer 18B) which had area 0.15 cm² and the surface exposed edge; C2044,20A,41,0,0 (wafer 20A) had area 0.24 cm² and was located below C2044,20B,41,0,0 (wafer 20B), which had area 0.20 cm² and the surface exposed edge. The entire wafer C2044,19,41,0,0 (wafer 19), area 0.41 cm², was analyzed as a single sample.

(b) *T41 Cross-Sectional Slice Samples:* Four adjacent cross-sectional transverse slices through the T41 bulb were prepared. The four slices were an indeterminate distance from the top of the track 41 block, and each was ~200 µm thick (Fig. 8A). The topmost slice, relative to the surface of the track 41 block, was C2044,8,41,0,0 (CRPG “slice 1”) and immediately below it was C2044,9,41,0,0 (CRPG “slice 2”). Below slice 9 was slice 17 and directly below that was slice 18. These four slices were prepared after the keystone was removed containing the T41 material analyzed in Marty et al. (2008). Slices 17 and 18 were trimmed and made into three analyzed samples (Fig. 3): (1) C2044,17,41,0,0 consisted of material from only slice 17; (2) C2044,17&18,41,0,0 consisted of aerogel pieces combined from both slices 17 and 18; and (3) C2044,18,41,0,0 contained only aerogel from the lowest of the four slices, slice 18.

(c) *Blank Block Surface and Subsurface Samples:* The blank block surface slice sample had a nonuniform thickness (Fig. 4) and was divided into four fragments. Surface fragment 0 was kept at UC Berkeley, and surface fragments 1–3 were sent to the University of Minnesota (UM) for analysis. These surface fragments

Westphal A. J., Bridges J. C., Brownlee D. E., Butterworth A. L., De Gregorio B. T., Dominguez G., Flynn G. J., Gainsforth Z., Ishii H. A., Joswiak D., Nittler L. R. T., Ogliore R. C., Palma R., Pepin R. O., Stephan T., and Zolensky M. E. 2017. The future of Stardust science. *Meteoritics & Planetary Science* 52:1859–1898.

Ziegler J. F. 2004. SRIM-2003. *Nuclear Instruments and Methods in Physics B* 219–220:1027–1036.

had internal, UM designations: St-C44s1,1 (area ~14.3 mm²), St-C44s1,2 (area ~8.0 mm²), and St-C44s1,3 (area ~7.7 mm²), where fragment surface areas were calculated from the dimensions shown in Fig. 4B. The subsurface slice (Fig. 5) was 200 µm thick except around the edge, and was subdivided into four fragments. Subsurface fragment 3 was kept at UC Berkeley, and subsurface fragments 1, 2, and 4 were sent to UM. These subsurface fragments were designated at UM as St-C44s2,1, St-C44s2,2, and St-C44s2,4.

(d) *T41 Fragment Samples:* An aerogel fragment containing melted aerogel from the T41 wall was subdivided into five smaller samples (Fig. 6). Three of these five samples were sent to UM (C2044,28,41,0,0, C2044,30,41,0,0, and C2044,31,41,0,0) and two were sent to CRPG (C2044,29,41,0,0, and C2044,32,41,0,0). A “blank” sample was also prepared from the same fragment and sent to UM (“δ2 blank”). This “blank” sample did not contain visible melted aerogel from the T41 wall but was at most a few mm from the T41 wall.

(e) *Blank Block Samples:* The blank block was further subdivided after the three wafers discussed in (a) above were cut vertically from the end of the block furthest from T41, and the 2 slices discussed in (c) above were cut horizontally from the top of the block. The first set of small blank block samples was created from an ~1 mm wide, ~9 x ~9 mm square of aerogel cut from the blank block surface adjacent to the track 41 block. This rectangular box was subdivided into ~9 mm tall vertical columns of approximately 1 x 1 mm cross section, and the columns were then cut horizontally into the final sample blocks of ~1–1.5 mm³ (Fig. 7). Additional columns and similar block samples were later created from the remaining blank block material (Fig. 8). Overall, a total of 122 of these blank block samples were created, 70 of which were analyzed at UM and 19 at CRPG. The analyzed samples were from random depths from the space-exposed surface (up to ~9 mm depth), and at random distances from the T41 axis.

## 2) OTHER CELL SAMPLES

(a) *C2028 Surface Samples:* M. Zolensky and the Astromaterials Acquisition and Curation Facility,
NASA-Johnson Space Center, prepared five samples from the surface of aerogel cell C2028 (Fig. 9). These samples were all ~100 µm thickness slices taken from keystones. Four smaller slices (C2028,6; C2028,7; C2028,8; and C2028,9) came from different parent keystones and were combined into a single sample C2028,6-9,0,0 (UM designation C2028-2). The combined area of the samples making up C2028-2 was ~0.5 cm², approximately the same as that of the largest slice sample, C2028,13-14,0,0 (UM designation C2028-1), which was a combination of two cross-sectional slices from the same parent keystone. These samples were crushed and loaded in Pt foils as discussed in the Gas Extraction and Analysis section.

(b) *C2086 Samples*: Three sets of samples were prepared from cell C2086 (Figs. 10 and 11), and the samples are referred to by the shorthand notations in Figs. 19–21. The first set included eight “blank” aerogel samples (“blks 1-8”) taken from various locations on the cell without visible cometary material, entire track T181, and procedural Pt foil 1 to monitor cutting dust distribution. The second set included entire track T182, procedural foil 2, and a handpicked surface contaminate sample nicknamed “schmutz.” The third and last set of five samples was “A1-3” and “BD1-2”; again, “blank” aerogel samples without visible cometary fragments.

The contaminate material sampled by “schmutz” is found on only a tiny fraction of aerogel tile surfaces, including C2086. This material is probably a relic from aerogel manufacturing. It has never been analyzed, so it

is not clear what it may be. Although it contains low but measurable helium and neon abundances (Table 1), this “schmutz” is a handpicked concentrated sample of material that is actually thinly distributed on tile surfaces. We therefore assume that its impact on our aerogel noble gas measurements is negligible.

(c) *T108 Terminal Particles*: K. Nakamura-Messenger of NASA-Johnson Space Center isolated and prepared three 15–20 µm individual terminal particles from aerogel cell C2081, T108 (Fig. 12), samples C2081,1,108,12,0, C2081,1,108,13,0, and C2081,1,108,14,0. Particles 13 and 14 were packaged together for analysis, while particle 12 was analyzed individually.

(d) *T77 Terminal Particle*: D. Brownlee of the University of Washington provided a terminal particle from aerogel cell C2009, T77, nicknamed “Puki A.” This sample was an 11.5 × 9 µm pure olivine grain previously analyzed by transmission electron microscopy (Leroux 2009) and for oxygen isotopes (Nakashima et al. 2012). It had been studied by ion probe (three 1.5 µm holes), but Brownlee (personal communication) estimated that almost all of the 3.4 ng mass was still intact. The sample came encased within a 200 × 200 × 110 µm acrylic cube.

(e) *Interstellar Collector Surface and Subsurface Samples*: Two surface and two subsurface aerogel samples without discernible particles were prepared from a 200 µm wide keystone taken from the interstellar side of the Stardust collector, aerogel cell I1047 (Fig. 13).