Presentation Information
[R5-13]Bulk Density, Porosity, and Fe/Mg Ratio of Bennu Particle Matrices: Comparison with Ryugu and Carbonaceous Chondrites.
*Akira TSUCHIYAMA1, Megumi Matsumoto2, Masanori Yasutake3, Junya Matsuno4, Kentaro Uesugi3, Akihisa Takeuchi3, Toru Matsumoto5, Haruka Ohno6, Mingqi Sun7, Tomoyo Morita2, Shogo Tachibana8, Harlord C Connolly9, Dante S Lauretta10 (1. Ritsumeikan Univ. ROST, 2. Tohoku Univ. Sci., 3. JASRI/SPring-8, 4. Kyoto Univ. ICR, 5. Kyoto Univ. Hakubi, 6. Kyoto Univ. Sci., 7. CAS/GIG, 8. Univ. Tokyo Sci., 9. Rowan Univ., 10. Univ. Arizona)
Keywords:
X-ray nanotomography,SPring-8,OSIRIS-REx mission,Hayabusa2 mission,CI chondrites
We determined the matrix bulk density, porosity, and Mg# [Mg/(Mg + Fe) atom ratio] of particles returned from asteroid Bennu by the OSIRIS-REx mission [1], and we compared them with those of other aqueously altered carbonaceous astromaterials, including asteroid Ryugu and chondrites. The analyzed Bennu particles (5–50 μm) were picked from unsorted aggregate samples (OREX-803143-0, OREX-803118-0), either directly or by FIB extraction from larger particles. At SPring-8 beamline BL47XU, 3D X-ray computed tomography images were acquired at 7 and 7.35 keV (absorption contrast) and 8 keV (phase contrast), with a spatial resolution of ~200 nm [2]. Our calculations assumed that the matrix is composed of phyllosilicates, organic matter, and pores based on the Bennu matrix mineralogy [1], using the linear attenuation coefficients and refractive index decrement (proportional to density). The matrix properties of the aqueously altered samples were as follows:
Bennu (N= 16): bulk density = 1.6 ± 0.3 (1.2–2.3) g/cm³, porosity = 39 ± 12 (16–57) %, Mg# = 0.77 ± 0.11 (0.48–0.91)
Ryugu (N = 72):8 ± 0.2 (1.4–2.2) g/cm³, 32 ± 9 (18–48) %, 0.83 ± 0.06 (0.66–0.93)
CI (N = 16):1 ± 0.1 (1.9–2.3) g/cm³, 22 ± 5 (12–31) %, 0.79 ± 0.06 (0.64–0.89)
CM (N = 7):2 ± 0.2 (1.9–2.4) g/cm³, 20 ± 6 (13–28) %, 0.63 ± 0.11 (0.44–0.77)
Tagish Lake (N = 5):1 ± 0.0 (2.1–2.2) g/cm³, 19 ± 1 (19–21) %, 0.84 ± 0.06 (0.76–0.89)
Although Bennu and Ryugu samples are similar to CIs and each other [1,2], some Bennu matrices exhibited lower density, higher porosity, and lower Mg# than Ryugu matrices. CI matrices had generally higher density, lower porosity, and lower Mg# than Bennu and Ryugu matrices, likely due to terrestrial weathering. CM and Tagish Lake matrices were similar to CIs’, except for the CMs’ more Fe-rich composition.
[1] Lauretta & Connolly et al. (2024) MAPS 59, 2453–2486. [2] Tsuchiyama et al. (2024) GCA 375, 146–172.
Bennu (N= 16): bulk density = 1.6 ± 0.3 (1.2–2.3) g/cm³, porosity = 39 ± 12 (16–57) %, Mg# = 0.77 ± 0.11 (0.48–0.91)
Ryugu (N = 72):8 ± 0.2 (1.4–2.2) g/cm³, 32 ± 9 (18–48) %, 0.83 ± 0.06 (0.66–0.93)
CI (N = 16):1 ± 0.1 (1.9–2.3) g/cm³, 22 ± 5 (12–31) %, 0.79 ± 0.06 (0.64–0.89)
CM (N = 7):2 ± 0.2 (1.9–2.4) g/cm³, 20 ± 6 (13–28) %, 0.63 ± 0.11 (0.44–0.77)
Tagish Lake (N = 5):1 ± 0.0 (2.1–2.2) g/cm³, 19 ± 1 (19–21) %, 0.84 ± 0.06 (0.76–0.89)
Although Bennu and Ryugu samples are similar to CIs and each other [1,2], some Bennu matrices exhibited lower density, higher porosity, and lower Mg# than Ryugu matrices. CI matrices had generally higher density, lower porosity, and lower Mg# than Bennu and Ryugu matrices, likely due to terrestrial weathering. CM and Tagish Lake matrices were similar to CIs’, except for the CMs’ more Fe-rich composition.
[1] Lauretta & Connolly et al. (2024) MAPS 59, 2453–2486. [2] Tsuchiyama et al. (2024) GCA 375, 146–172.