In this study, systematic rock magnetic measurements and saturation isothermal remanent magnetization (SIRM) paleointensity calibration experiments were conducted for the returned samples from C-type asteroid (162173) Ryugu and two carbonaceous chondrites (Orgueil and Tagish Lake) to evaluate the remanence carriers of the Ryugu sample and its ability as a paleomagnetic recorder. Our magnetic measurements show that Ryugu samples exhibit signatures for framboidal magnetite, coarse-grained magnetite, and pyrrhotite, and that framboidal magnetite is the dominant remanence carrier of Ryugu samples in the middle-coercivity range. The SIRM paleointensity constant was obtained for two Ryugu samples, and the median value was 3,318 ± 1,038 μT, which is close to the literature's value based on the average among magnetite, titanomagnetite, pyrrhotite, and FeNi alloys and is widely used for SIRM paleointensity experiments. The paleointensity values estimated using the obtained SIRM paleointensity constant indicate a strong magnetic field of the protoplanetary disk, suggesting that Sun's protoplanetary disk existed at the disk location of Ryugu's parent planetesimal when framboidal magnetite precipitated from the aqueous fluid.

Key Points

Rock magnetic properties and paleointensity constant are investigated for returned samples from C-type asteroid (162173) Ryugu
Framboidal magnetites dominate stable natural remanence components of Ryugu samples in a middle-coercivity range
Paleointensity values estimated using our paleointensity constant indicate a strong magnetic field of the protoplanetary disk

Plain Language Summary

Knowledge of rock magnetic properties is crucial to interpret a remanence record of sample and to reconstruct a reliable past magnetic field intensity value. Rock magnetic measurements and saturation isothermal remanent magnetization (SIRM) magnetic field intensity calibration experiments were conducted on returned samples from C-type asteroid (162173) Ryugu and two meteorite samples (Orgueil and Tagish Lake) to evaluate the remanence carriers of the Ryugu sample and its ability as a past magnetic field recorder. Magnetic field intensity values estimated on the basis of newly obtained rock magnetic properties and SIRM magnetic field intensity constant indicate a strong magnetic field of the protoplanetary disk, suggesting that Sun's protoplanetary disk existed at the disk location of Ryugu's parent planetesimal when framboidal magnetite precipitated from the aqueous fluid.

1 Introduction

Knowledge of the evolution of the magnetic field structure in the early solar system is key to understanding the evolution of protoplanetary disks and synchronous/subsequent planet formation (e.g., Weiss et al., 2021). Ferromagnetic minerals in meteorites acquired and have occasionally retained magnetic field information as natural remanent magnetization (NRM). Time-spatial variations in the magnetic field in Sun's protoplanetary disk have been reconstructed from the meteorite samples recording chemical remanent magnetization (CRM) with/without partial thermal remanent magnetization (pTRM) (Borlina et al., 2022; Bryson, Weiss, Lima, et al., 2020; Cournede et al., 2015; Fu et al., 2021; Gattacceca et al., 2016), the meteorite samples recording thermoremanent magnetization (TRM) (Bryson, Weiss, Biersteker, et al., 2020; Wang et al., 2017), and the chondrules that acquired TRM during their formation (Borlina et al., 2021; Fu et al., 2014, 2020). However, the time-spatial evolution of the disk magnetic field has not been fully constrained, because of the limitation of meteorite samples suitable for paleomagnetic recorders of various time/location in the solar nebula and the experimental difficulty in paleointensity reconstruction, and more work is clearly required to further constrain the time-spatial evolution of the solar nebula field.

The Hayabusa2 spacecraft collected samples from the surface of the C-type near-Earth asteroid (162173) Ryugu at two locations and transported them to Earth in December 2020 (Morota et al., 2020; Tachibana et al., 2022). The Ryugu samples offer a unique opportunity to investigate the magnetic field of the early solar system because they have been minimized the effects of weathering and magnetic field contamination on Earth, such as viscous remanent magnetization (VRM) in the geomagnetic field and the isothermal remanent magnetization (IRM) of artificial magnets, both of which make paleointensity experiments difficult. Moreover, the Ryugu samples give opportunity to compare magnetic records from asteroids with those of meteorites. The NRM measurements and paleointensity estimation were conducted in the context of the comprehensive analyses and calculations to understand the formation and evolution history of asteroid Ryugu (Nakamura et al., 2022). Two Ryugu samples showed stable NRM vector components toward the origin in orthogonal vector plots, and the preliminary paleointensity estimation based on a saturation IRM (SIRM) paleointensity method, called the REM' method (Gattacceca & Rochette, 2004), suggested strong paleointensity values from 18 to 704 μT (Nakamura et al., 2022). The large uncertainty in their paleointensity estimates using SIRM paleointensity method is mainly due to the lack of rock magnetic information, such as origins and carriers of stable NRM components and their SIRM paleointensity constants; thus, systematic rock magnetic experiments for the Ryugu sample are required to obtain reliable paleointensity values.

This study conducted systematic rock magnetic measurements and SIRM paleointensity calibration experiments on Ryugu samples and two carbonaceous chondrites (Orgueil and Tagish Lake) to evaluate the remanence carriers of the Ryugu sample and its ability as a paleomagnetic recorder and to improve the understanding of its NRM record. Orgueil was used in this study because it is classified as the CI chondrite with which the Ryugu sample shows the closest relationship from chemical and mineralogical perspectives (Nakamura et al., 2022; Yokoyama et al., 2022). Tagish Lake was also investigated in this study, because it contains framboidal magnetites and the framboidal magnetites contribute significantly to the NRM of Ryugu sample (Nakamura et al., 2022). On the basis of rock magnetic properties, this study reports the magnetic characteristics and remanence acquisition efficiencies of Ryugu samples.

2 Method

2.1 Samples

Asteroid Ryugu is a rubble-pile body with a spinning-top shape (Sugita et al., 2019; Watanabe et al., 2019). Hayabusa2 performed two touchdown operations on Ryugu on February 21 (TD1) and July 11 (TD2), 2019 (Morota et al., 2020; Tachibana et al., 2022), and stowed surface samples collected from these two TD sites in chambers A and C of the sample catcher (Sawada et al., 2017), respectively. The TD2 landing site was close to the artificial impact crater (Arakawa et al., 2020), and the TD2 sample was expected to contain subsurface materials excavated by the artificial impact. The pebbles and sand inside chambers A and C are representative samples of Ryugu at two landing sites (Tachibana et al., 2022). Magnetic measurements were conducted for particles in chambers A (A0026, A0064-FC006, and A0064-FO018) and C (C0002-4-f, C0002-40, and C0023-FC009). Grains C0002-4-f and C0002-40 were fragments of a centimeter-sized grain C0002, the third largest of all the returned grains. Magnetic measurements of Ryugu C0002-40 were conducted after heating to 600°C in a vacuum to evaluate the effect of laboratory heating on the magnetic properties. The Orgueil and Tagish Lake carbonaceous chondrites were obtained from the N's Mineral Co., Ltd., Japan and the La Memoire de la Terre SARL, France, respectively, and were measured for comparison. A summary of the sample information and the measurement sequences is presented in Table 1.

Table 1. Summary of Experimental Samples

Sample	Size (mm)	Mass (mg)	Remark	Measurement sequence of this study
Ryugu
A0026	∼1	1.556	–	Low-temperature remanence curves and hysteresis curves^a
A0064-FC006	∼1	N/A	Fragment of a grain A0064	Hysteresis curves and FORC
A0064-FO018	∼0.1	N/A	Fragment of a grain A0064	NRM/IRM/TRM/IRM_H measurements
C0002-4-f	∼1	0.425	Fragment of a grain C0002	Low-temperature remanence curves, IRM gradient curves, and hysteresis curves^a
C0002-40	∼1	N/A	Fragment of a grain C0002	Heating twice, low-temperature remanence curves, IRM gradient curves, and hysteresis curves
C0023-FC009	∼0.1	N/A	Fragment of a grain C0023	NRM/IRM/TRM/IRM_H measurements
Chondrite
Orgueil	∼1	N/A	–	IRM/TRM/IRM_H measurements
–	∼1	0.77	–	Low-temperature remanence curves, IRM gradient curves, and hysteresis curves
Tagish Lake	∼1	N/A	–	IRM/TRM/IRM_H measurements
–	∼1	1.09	–	Low-temperature remanence curves, IRM gradient curves, and hysteresis curves

^a Natural remanent magnetization (NRM) and isothermal remanent magnetization (IRM) were measured before low-temperature remanence curves (Nakamura et al., 2022). FORC: first-order reversal curve; TRM: thermoremanent magnetization; IRM_H: IRM after laboratory heating.

The Ryugu particles were passed through and stored on the components made of non-magnetic aluminum alloys (Sawada et al., 2017). The distances from Ryugu particle to the magnetic- and electrical-components of Hayabusa2 spacecraft were at least larger than 0.4 mm in passing through the sampler hone, 4 mm in the sample catcher transferring into capsule, and 16 mm after sealing the sample container (Sawada et al., 2017). The temperature monitor attached to the sample container indicated that the container had never heated up to 65°C (Yada et al., 2022). The Ryugu particles in the sample container had experienced the several tens of microtesla field from the magnetic moment of ion engine system (∼100 Am², Yoshikawa et al., 2016) during transport from Ryugu to Earth. The Ryugu particles were stored on the curation facility in the Japan Aerospace Exploration Agency, and the particles had been kept their orientation during 4–6 months. After the period, the samples were frequently moved and changed their orientations until magnetic measurements.

2.2 Rock Magnetic Experiment

In order to evaluate the ferromagnetic mineral components and their contribution to remanent magnetizations, a suite of rock magnetic measurements was conducted for the Ryugu, Orgueil, and Tagish Lake samples. Low-temperature remanence curves were measured for the Ryugu (A0026, C0002-4-f, and C0002-40), Orgueil, and Tagish Lake samples, to investigate the composition of ferromagnetic minerals. These curves comprise of (1) a thermal demagnetization (THD) curve of IRM imparted at 10 K in a field of 2.5 T after zero-field cooling (ZFC remanence), (2) a THD curve of remanence given by field cooling from 300 to 10 K in a field of 2.5 T (FC remanence), and (3) a low-temperature demagnetization (LTD) cycle of SIRM imparted at 300 K in a field of 2.5 T (room temperature SIRM, RT-SIRM). An IRM gradient curve was used for identifying the ferromagnetic mineral components with respect to remanent magnetization and obtained by applying a direct current (DC) field of 4 T and, subsequently, stepwise-increasing DC back fields at 36 steps from 1 mT to 4 T. The first derivative of the acquisition curve was calculated with respect to log₁₀ field. The IRM gradient curves were measured at room and low temperatures for Ryugu C0002-4-f (7 points between 10 and 300 K), Ryugu C0002-40, Orgueil, and Tagish Lake samples (10 and 300 K). The magnetic hysteresis loop and direct field demagnetization curves were measured at 10–300 K for the Ryugu (A0026, C0002-4-f, and C0002-40), Orgueil, and Tagish Lake samples, to characterize the magnetic domain state of ferromagnetic minerals and their temperature characteristics. The low-temperature remanence, IRM gradient, and magnetic hysteresis curve measurements were performed using magnetic property measurement systems (MPMS3 and MPMS-5S, Quantum Design) at the Cryogenic Research Center, University of Tokyo. Additionally, the hysteresis loop, direct-field demagnetization curve, and first-order reversal curve (FORC) were measured for the Ryugu A0064-FC006 sample by using a vibrating sample magnetometer (MicroMag 3900, Princeton Measurements Corporation) at the University of Tokyo. The FORC diagram can be used for identifying the ferromagnetic mineral components with respect to induced magnetization. Note that A0026 and A0064-FC006 are particles collected at the first touchdown (TD1) location and that C0002-4-f and C0002-40 are fragments of the same particle (C0002) collected at the second touchdown (TD2) site.

In order to evaluate the effect of VRM acquired during transportation and on Earth, the NRM vector of A0064-FO018 and C0023-FC009 samples were measured before and after the remanence relaxation in a magnetic shield case for 2–3 months prior to the SIRM paleointensity calibration experiment.

2.3 SIRM Paleointensity Calibration Experiment

For the investigation of the relationship between the remanence carriers and their behavior in paleointensity experiments, the SIRM paleointensity method was verified for the Ryugu (A0064-FO018 and C0023-FC009), Orgueil, and Tagish Lake samples. Note that A0064-FO018 and C0023-FC009 are fragments of grains A0064 (collected at the TD1 site) and C0023 (collected at the TD2 site), respectively. The sequence of the SIRM paleointensity calibration experiment was as follows: (1) IRM was imparted with a field of 2.5 T by using a pulse magnetizer (IM-10-30 Impulse Magnetizer, ASC Scientific); next, stepwise alternating field demagnetization (AFD) was conducted on IRM. (2) The TRM was imparted by heating up to 600°C for 5 min and cooling back to room temperature with a 103 μT DC field (B_TRM), and the resultant TRM was measured with stepwise AFD treatments same as the IRM sequence. The heating and cooling procedures were conducted under vacuum (<5 Pa) using a TDS-1 thermal demagnetizer (Natsuhara-Giken). (3) IRM was imparted with a field of 2.5 T (referred to as IRM_H), and stepwise AFD treatments same as the IRM sequence were conducted. (4) The SIRM paleointensity constant was calculated using the slope in the TRM-IRM_H diagram (S_{TRM-IRM_H}) as B_TRM × S_{TRM-IRM_H}. Because the magnetic minerals in Ryugu samples underwent thermal alteration during TRM acquisition treatment, the magnetic minerals contributed to TRM state was same as IRM_H state while it was different from IRM state. Then, the slope of TRM-IRM_H diagram was used to calculate the paleointensity constant rather than that of the TRM-IRM diagram.

The sample holder of paleointensity calibration experiment was same as that in Kato et al. (2018) used for a single crystal plagioclase measurement. An approximately 1 mm diameter pit was drilled in the center of a non-alkali high-temperature glass (Eagle XG, Corning) with a square shape of 8 × 8 mm and 1.1 mm thick, and the drilled glass was used as a sample holder after cleaning in 6M HCl. The paleointensity calibration samples were placed in the pit and fixed by stuffing SiO₂ powder. Remanence measurements were conducted using a superconducting quantum interference device magnetometer (Model 755, 2G Enterprise) at the University of Tokyo. The remanence measurement method of paleointensity calibration experiment was following that in Sato et al. (2015) used for a single crystal zircon measurement. The sample holder was set at the edge of a rod made of polylactic acid by using double-sided tape. The remanence of the polylactic acid rod was measured before and after the sample measurement, and the averaged remanence of the rod was subtracted to calculate the sample moment.

3 Results

3.1 Rock Magnetic Properties

The low-temperature remanence curves of the Ryugu C0002-4-f sample are shown in Figure 1a. The ZFC and FC remanence curves show a sharp decline at approximately 120 K and small inflections at approximately 30 K, corresponding to the low-temperature transitions of nearly stoichiometric magnetite (Moskowitz et al., 1998) and pyrrhotite (Dekkers et al., 1989), respectively. RT-SIRM was significantly demagnetized at approximately 120 K during the LTD cycle, and the intensity of RT-SIRM decreased to ∼77% of the original value after the LTD cycle, indicating the presence of fine-grained magnetite (Heider et al., 1992).

Details are in the caption following the image — **Figure 1**
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Magnetic properties of the experimental samples. (a) Zero-field cooling (ZFC) remanence, field cooling (FC) remanence, and low-temperature demagnetization cycle of room temperature saturation isothermal remanent magnetization (RT-SIRM) for Ryugu C0002-4-f sample. Arrows indicate warming and cooling directions. Reduction in the RT-SIRM intensity is marked as dotted arrow. The temperature values of 30 and 120 K are shown by vertical dotted lines as a guide for the eye. (b) First derivative of the isothermal remanent magnetization (IRM) acquisition curve is plotted with respect to the applied field for Ryugu C0002-4-f sample. The applied field values of 5, 70, and 200 mT are shown by vertical dotted lines as a guide for the eye. (c) The ratio of magnetic hysteresis parameters (saturation IRM M_rs, saturation magnetization M_s, coercivity of remanence B_cr, and coercivity B_c) for Ryugu (A0026, A0064-FC006, C0002-4-f, and C0002-40), Orgueil, and Tagish Lake samples. The SD, PSD, and MD indicate single-domain (SD), pseudo-SD (PSD), and multidomain (MD) region. Literature data for Orgueil, Tagish Lake, and WIS 91600 from Thorpe et al. (2002) and Sridhar et al. (2021) are also plotted in gray symbols. (d) B_c estimated from hysteresis loop is plotted as a function of temperature for Ryugu (C0002-4-f and C0002-40), Orgueil, and Tagish Lake samples. The hysteresis parameters of Ryugu C0002-40 sample were measured after twice heating to 600°C in vacuum condition. The temperature values of 30, 120, 210, and 260 K are shown by vertical dotted lines as a guide for the eye. (e) First-order reversal curve (FORC) diagram for Ryugu A0064-FC006 sample. The FORC distribution is plotted as functions of coercivity (B_c) and interaction field (B_u).

The IRM gradient curve for the Ryugu C0002-4-f sample is shown in Figure 1b. The gradient curve at 300 K showed a clear peak at approximately 70 mT and humps at approximately 5 and 200 mT. The latter hump shifted toward high coercivity with decreasing temperature, and the clear peak position with coercivity at approximately 2 T separated from the lower coercivity peak below 200 K. By contrast, the coercivities of the peak at approximately 70 mT and hump at approximately 5 mT were almost constant at 10–300 K. The temperature changes in the IRM gradient curve indicate the presence of three families of minerals that contribute to the magnetic mineralogy of the Ryugu particles. Considering the coercivity ranges of magnetic minerals and these temperature dependences, the components with peak at approximately 70 mT and hump at approximately 5 mT are likely fine-grained and coarse-grained magnetites, respectively, and the component with hump at approximately 200 mT is considered to be pyrrhotite.

The magnetic hysteresis measurements for the Ryugu C0002-4-f sample are summarized in Figures 1c and 1d and Table 2. Ratios of the magnetic hysteresis parameters (SIRM M_rs, saturation magnetization M_s, coercivity of remanence B_cr, and coercivity B_c) were plotted on the pseudo-single-domain (PSD)/multidomain (MD) boundary region in the Day plot (Day et al., 1977). The temperature dependence of B_c showed a small inflection at approximately 30 K and a sharp decline at approximately 120 K, corresponding to the low-temperature transitions of pyrrhotite and magnetite, respectively (Figure 1d). A concave upward shape between 120 and 300 K with a maximum at approximately 210 K was observed in the temperature-B_c curve (Figure 1d). The concave-up feature resembles the temperature dependence of the magnetocrystalline anisotropy of magnetite (Dunlop & Özdemir, 1997), suggesting that the magnetocrystalline anisotropy energy dominates the magnetic properties of magnetite particles in the Ryugu sample above 120 K.

Table 2. Magnetic Hysteresis Parameters of Experimental Samples

Sample	M_s (Am²/kg)	M_rs (Am²/kg)	B_c (mT)	B_cr (mT)	M_rs/M_s × 10⁻²	B_cr/B_c
Ryugu A0026	11.8	1.07	11.8	59.9	9.11	5.08
Ryugu C0002-4-f	11.3	1.01	12.2	63.2	8.93	5.18
Ryugu A0064-FC006	–	–	10.2	47.0	8.52	4.59
Ryugu C0002-40 after heating	–	–	5.4	30.4	2.14	5.60
Orgueil	9.7	0.52	11.1	48.2	5.38	4.34
Tagish Lake	8.3	0.17	5.1	29.4	1.99	5.71

Note. M_s: saturation magnetization; M_rs: saturation isothermal remanent magnetization; B_c: coercivity; B_cr: coercivity of remanence.

The FORC diagram of the Ryugu A0064-FC006 sample was calculated from the FORC curves with a smoothing factor of 6, using FORCinel software (Harrison & Feinberg, 2008) (Figure 1e). The FORC diagram shows a distinct triangular shape extending vertically to 100 mT and horizontally to 100 mT. The FORC distribution is interpreted as the signature of closely packed and interacting grains (Harrison et al., 2019). The distinct triangular distributions were similar to the FORC distributions in carbonaceous chondrites with framboidal magnetite such as Orgueil (Sridhar et al., 2021), Tagish Lake (Bryson, Weiss, Lima, et al., 2020), and WIS 91600 (Bryson, Weiss, Biersteker, et al., 2020; Sridhar et al., 2021).

The low-temperature remanence curve of the A0026 sample (Figure 2a) and the hysteresis parameters (Table 2) of the A0026 and A0064-FC006 samples from landing site TD1 on Ryugu are consistent with those of the C0002-4-f sample from another landing site, TD2, and a reasonable assertion that the aforementioned magnetic features are representative characteristics of the surface samples of asteroid Ryugu. Systematic rock magnetic measurements revealed that the Ryugu sample contained coarse-grained magnetite, fine-grained magnetite, and pyrrhotite, which is consistent with the mineralogical and petrological analyses of Ryugu samples (Nakamura et al., 2022).

The Ryugu C0002-40 sample after two heating cycles showed magnetite signatures, such as the decline at approximately 120 K in the ZFC and FC remanence curves (Figure 2b), the demagnetization of RT-SIRM at approximately 120 K during the LTD cycle (Figure 2b), the peak and hump below 100 mT in the IRM gradient curves (Figure 3a), and the change in B_c values at approximately 120 K (Figure 1d). By contrast, the signatures of pyrrhotite, such as the inflections at approximately 30 K (ZFC and FC remanence curves and temperature change in B_c value) and the high-coercivity component above 200 mT (IRM gradient curves), were hardly recognized in the heated sample. Thus, because of laboratory heating, the amount of pyrrhotite decreased considerably, and those of fine-grained and coarse-grained magnetites decreased to some extent.

The NRM intensities of A0064-FO018 and C0023-FC009 samples were 4.50 × 10⁻¹¹ and 3.13 × 10⁻¹¹ Am², respectively. The changes in NRM vector of A0064-FO018 and C0023-FC009 samples before and after the relaxation for 2–3 months were 1.6 × 10⁻¹² and 1.9 × 10⁻¹² Am², respectively, which were less than 6% of NRM intensities.

The rock magnetic properties of the Orgueil and Tagish Lake samples were similar to those of the Ryugu samples. The ZFC and FC remanence curves of the Orgueil and Tagish Lake samples showed sharp declines at approximately 120 K and small inflections at approximately 30 K, and the RT-SIRM of the Orgueil and Tagish Lake samples significantly demagnetized at approximately 120 K during the LTD cycle (Figures 2c and 2d). The IRM gradient curves of the Orgueil and Tagish Lake samples showed humps below 10 mT and peaks in the 20–200 mT range at 300 K, and the humps and peaks slightly shifted toward high coercivity at 10 K (Figures 3b and 3c). A sharp decline at approximately 120 K and concave-up shapes above 120 K were observed in the temperature-B_c diagrams for the Orgueil and Tagish Lake samples (Figure 1d). The inflection at approximately 30 K was recognized for the Tagish Lake sample, and the inflection was ambiguous for the Orgueil sample (Figure 1d). A small hump at approximately 260 K was observed in the temperature dependence curves of B_c for the Orgueil and Tagish Lake samples (Figure 1d), which may indicate the effect of the surface oxidation of magnetic minerals due to weathering on Earth's surface. Despite these differences, the overall magnetic features of the Orgueil and Tagish Lakes were similar to those of the Ryugu samples.

3.2 SIRM Paleointensity Calibration Experiment

The results of the SIRM paleointensity calibration experiment for the Ryugu A0064-FO018 and C0023-FC009 samples are summarized in Figures 4 and 5 and Table 3. The IRM, TRM, and IRM_H vectors of these samples systematically decreased to their origins in the orthogonal vector plots with the maximum angular deviation (MAD) of 1.0–15.7° and deviation angle (DANG) of 0.7–16.7° (Figures 4a–4c and 5a–5c). The effect of thermal alteration due to TRM heating was evaluated using the relationship between IRM and IRM_H (Figures 4d and 5d). Linear portions existed up to the 24 and 14 mT AF ranges in the IRM-IRM_H diagram for the Ryugu A0064-FO018 and C0023-FC009 samples, respectively. The IRM-IRM_H plots were deflected from the linear trends above these AF steps, and the IRM_H intensities significantly decreased above 50 mT AF steps with respect to the IRM intensities. The linear portions both in the TRM-IRM_H and IRM-IRM_H diagrams were recognized in the 4–24 and 4–14 mT AF ranges for the Ryugu A0064-FO018 and C0023-FC009 samples, respectively (Figures 4d, 4e, 5d, and 5e). Hereinafter, these AF ranges with linear trends are defined as middle-coercivity range, and the AF ranges below 4 mT and above middle-coercivity range are defined as low- and high-coercivity ranges, respectively. The SIRM paleointensity constants using the slopes of the TRM-IRM_H diagrams in these linear AF segments were estimated to be 4,053 ± 260 μT and 2,584 ± 135 μT for the Ryugu A0064-FO018 and C0023-FC009 samples, respectively. The median value and standard deviation of the paleointensity constant were 3,318 ± 1,038 μT. The errors in slope estimations, mainly due to the uncertainty in remanence measurements (noise level 10⁻¹² Am²), were significantly smaller than the interparticle variation in slope values.

Table 3. Summary of Saturation Isothermal Remanent Magnetization Paleointensity Calibration Experiments

Sample	Segment (mT)	Paleointensity constant (μT)
Ryugu A0064-FO018	4–24	4,053 ± 260
Ryugu A0064-FO018	4–50	3,813 ± 184
Ryugu C0023-FC009	4–14	2,584 ± 135
Ryugu C0023-FC009	4–50	2,429 ± 150
Orgueil	0–20	5,955 ± 260
Tagish Lake	0–20	5,742 ± 178

The results of the SIRM paleointensity calibration experiment for the Orgueil and Tagish Lake samples are summarized in Figures 6 and 7 and Table 3. Linear portions existed up to 20 mT AF steps in the IRM-IRM_H diagram for the Orgueil and Tagish Lake samples. In the case of the Orgueil sample, the IRM-IRM_H plot deflected from the linear trend above the 25 mT AF step, and the IRM_H intensity significantly decreased in the 50–200 mT AF range with respect to the IRM intensity. The Tagish Lake sample showed a slight deflection from the linear trend above the 25 mT AF step and contained almost no IRM components in the 50–200 mT AF range. The linear portions both in the TRM-IRM_H and IRM-IRM_H diagrams were recognized in the 0–20 mT AF ranges for the Orgueil and Tagish Lake samples, and the SIRM paleointensity constants obtained from these linear portions of the Orgueil and Tagish Lake samples were 5,955 ± 260 μT and 5,742 ± 178 μT, respectively.

4 Discussion

4.1 Magnetic Minerals in Ryugu Sample

Microscopic observations of the Ryugu samples revealed that they contained (1) framboidal magnetite with submicron to micron sizes; (2) hopper, plaquette, and spray-shaped magnetite above micron sizes; and (3) pyrrhotite from submicron to hundreds of microns in size (Nakamura et al., 2022). The fine-grained magnetite, coarse-grained magnetite, and pyrrhotite recognized from magnetic measurements are interpreted as fine-grained framboidal magnetite, coarse-grained hopper-, plaquette-, and spray-shaped magnetites, and pyrrhotite grains of various sizes.

The pyrrhotite components in the IRM gradient curves show a high coercivity above 100 mT and a significant increase in coercivity at low temperatures (Figure 1b), which is consistent with the coercivity range of pyrrhotite grains of submicron to hundreds of microns (O'Reilly et al., 2000) and the change in coercivity of pyrrhotite at low temperatures (Dekkers et al., 1989). The components with hump at approximately 5 mT and peak approximately 70 mT in the IRM gradient curves are consistent with the coercivity range of magnetite grains with submicron to micron and above micron sizes, respectively (Dunlop & Özdemir, 1997). Because the signature of equidimensional fine-grained magnetite is dominant in the low-temperature curves (Figure 1a), IRM gradient curves (Figure 1b), hysteresis parameters (Figures 1c and 1d), and FORC diagram (Figure 1e), in terms of the remanence contribution, the relative abundances of magnetic minerals are in the order corresponding to fine-grained magnetite, pyrrhotite, and coarse-grained magnetite. Therefore, a conclusion is that framboidal magnetite is the main remanence carrier of the Ryugu sample.

4.2 SIRM Paleointensity Constant for Ryugu Sample

The SIRM paleointensity constant changes depending on both the composition and domain state of the magnetic minerals, resulting in large uncertainty in the paleointensity estimate (Gattacceca & Rochette, 2004; Weiss & Tikoo, 2014). Framboidal magnetite has a unique texture in the Ryugu and some carbonaceous chondrite samples including Orgueil and Tagish Lake, and verification of the SIRM paleointensity constant is required to determine reliable paleointensity values from these samples.

Linear portions were recognized on both TRM-IRM_H and IRM-IRM_H diagrams in the 4–24 and 4–14 mT AF ranges for the Ryugu A0064-FO018 and C0023-FC009 samples (Figures 4 and 5), and these linear portions are the remanence behavior of framboidal magnetite considering the coercivity range of magnetic components. Three distinct features in the TRM-IRM_H and IRM-IRM_H diagrams should be considered to evaluate the SIRM paleointensity constant: deflections from linear trends in the high-coercivity range in the IRM-IRM_H diagram, deflections from linear trends in the low-coercivity range in the TRM-IRM_H diagram, and continuous linear trends from the middle-coercivity to high-coercivity ranges in the TRM-IRM_H diagram.

The slope of the linear portion in the IRM-IRM_H diagram for the Ryugu C0023-FC009 sample is almost one, and that of the Ryugu A0064-FO018 sample is smaller than unity because of the thermal alteration in TRM heating (Figures 4d and 5d). In the case of IRM_H state, compared with IRM state, the amount of framboidal and coarse-grained magnetites decreased to some extent, and that of pyrrhotite considerably decreased. The deflections from the linear trends in the high-coercivity range are caused by the depletion of pyrrhotite in IRM_H. The linear trend with slope of unity in the IRM-IRM_H diagram for the Ryugu C0023-FC009 sample indicates that the amount of framboidal and coarse-grained magnetites below 14 mT AF ranges were unchanged after laboratory heating as clearly seen in the gradient curve of IRM and IRM_H (Figure 5d). Moreover, the linear trend in the IRM-IRM_H diagram for the Ryugu A0064-FO018 sample indicates that the shape of the grain size distribution, that is, the grain number ratios for different grain sizes, of the framboidal and coarse-grained magnetites below 24 mT AF ranges after laboratory heating is almost identical to that of the original sample; the gradient curve of IRM_H for the Ryugu A0064-FO018 sample is smaller than that of IRM, while the gradient curve of IRM_H corrected by the slope of IRM-IRM_H diagram well agree with the IRM gradient curve below 24 mT AF ranges (Figure 4d). The linear trends in middle-coercivity continued up to 50 mT AF steps for the Ryugu A0064-FO018 and C0023-FC009 samples in the TRM-IRM_H diagrams (Figures 4e and 5e). Because the TRM and IRM_H were mainly imparted for framboidal and coarse-grained magnetites, the linear trends in the middle- and high-coercivity ranges are interpreted as the remanence behavior of framboidal magnetite, and the deflection in the low-coercivity range is caused by the difference in remanence behaviors between framboidal and coarse-grained magnetites.

The SIRM paleointensity constants using the slopes of the TRM-IRM_H diagrams in the 4–50 mT AF segments were estimated to be 3,813 ± 184 μT and 2,429 ± 150 μT for the Ryugu A0064-FO018 and C0023-FC009 samples, respectively, with median value and standard deviation of 3,121 ± 979 μT (Table 3). The paleointensity constant values are almost identical to those of narrow AF segments (3,318 ± 1,038 μT), and the paleointensity constants for the 4–50 mT AF segments probably represent the behavior of framboidal magnetite, supporting the reliability of the SIRM paleointensity constant obtained in the middle-coercivity range. Because the original Ryugu sample before heating contained pyrrhotite in the high-coercivity range, evaluating the SIRM paleointensity constant value for the high-coercivity range was difficult. Thus, this study proposes that the SIRM paleointensity constant of 3,318 μT is suitable for middle-coercivity framboidal magnetite in the original Ryugu samples.

The SIRM paleointensity constants obtained in this study and reported for equidimensional magnetite samples in Weiss and Tikoo (2014) are summarized in Figure 8. The constant values varied significantly with grain size, even in the case of equidimensional magnetite. The systematic increasing trend with increasing grain size ranging from 100 nm to 10 μm can be recognized for the paleointensity constant value of equidimensional magnetite, and the paleointensity constant values of the Ryugu sample are probably consistent with the grain size of framboidal magnetite in the Ryugu sample (∼1 μm, Nakamura et al., 2022), further supporting the applicability of the paleointensity constant in this study. The paleointensity constant values averaged for magnetite, titanomagnetite, pyrrhotite, FeNi alloys, and hematite were 3,000 μT (Gattacceca & Rochette, 2004) and 2,511 μT (Weiss & Tikoo, 2014) using different datasets. The constant values of 3,318 ± 1,038 μT for the Ryugu samples are close to the former constant and are widely used for SIRM paleointensity experiments, including carbonaceous chondrites (e.g., Cournede et al., 2015).

4.3 Comparison With Orgueil and Tagish Lake Samples

The pyrrhotite component (peak at approximately 0.5–1 T) is significantly smaller than the magnetite component in the Tagish Lake sample in the IRM gradient curve (Figure 3c), and the pyrrhotite/magnetite remanence ratio of the Ryugu sample is larger than that of the Tagish Lake sample (Figures 1b and 3c). The IRM gradient curve and temperature-B_c diagram of the Tagish Lake sample are similar to those of the Ryugu C0002-40 sample after heating twice, which contained magnetite and a relatively small amount of pyrrhotite. The difference between the hysteresis properties of the Tagish Lake and Ryugu samples can be explained by the small pyrrhotite contribution in the Tagish Lake sample; thus, the remanence carriers of the Tagish Lake sample are composed predominantly of framboidal magnetite and minor contributions of pyrrhotite and coarse-grained magnetite. This interpretation is consistent with the following: the linear trend below 20 mT AF steps in the IRM-IRM_H diagram is almost continuous above 20 mT AF steps (Figure 7d), and the linear trend below 20 mT AF steps in the TRM-IRM_H diagram continues up to 50 mT AF steps (Figure 7e).

The IRM gradient curve of the Orgueil sample at 300 K showed a broad distribution up to 300 mT, and the distribution was significantly distorted at 10 K. A significant shift toward high coercivity at 10 K was not observed for the Orgueil sample, suggesting that the pyrrhotite grains contribute little to the remanent magnetization. The RT-SIRM curve shows inflections at approximately 100 and 120 K, and a hump at approximately 280 K (Figure 2c). The broad and distorted distribution in the IRM gradient curves and inflection/hump in the RT-SIRM curve can be interpreted as the existence of surface-oxidized magnetite. The FC remanence curves were larger than the ZFC remanence curves between 10 and 300 K for the Ryugu C0002-4-f and Tagish Lake samples, largely because of the difference in the FC and ZFC remanences of pyrrhotite (Figures 1a and 2d). However, the FC remanence curves were smaller than the ZFC remanence curves for the Orgueil sample because of the lack of pyrrhotite remanences (Figure 2c). The Orgueil sample shows deflections from linear trends above 25 mT AF steps in both the IRM-IRM_H and TRM-IRM_H diagrams (Figures 6d and 6e). Framboidal magnetite dominates the remanence properties below 20 mT AF steps, and both the framboidal and surface-oxidized magnetites contribute to the remanence in 25–200 mT range, resulting in a different slope in the TRM-IRM_H diagram.

The signatures of equidimensional magnetite dominated the low-temperature remanence curves (Figures 2c and 2d) and temperature-B_c diagrams (Figure 1d) of the Orgueil and Tagish Lake samples in this study, and the distinct features of framboidal magnetite in the FORC diagrams were reported for Orgueil (Sridhar et al., 2021) and Tagish Lake (Bryson, Weiss, Lima, et al., 2020). Framboidal magnetites were the dominant remanence carrier in the middle-coercivity range for the Ryugu, Orgueil, and Tagish Lake samples, despite the aforementioned differences, and the linear portions were recognized on both TRM-IRM_H and IRM-IRM_H diagrams in the middle-coercivity ranges of these samples, further supporting the applicability of the paleointensity constant obtained for framboidal magnetite in middle-coercivity ranges.

4.4 Implications for Paleointensity Estimation

The one-step THD at 110°C for 5 min and subsequent stepwise AFD treatments on the NRM of the Ryugu A0026 and C0002-4-f samples showed stable components (Nakamura et al., 2022). In the process of the comprehensive analyses in Nakamura et al. (2022), the Ryugu A0026 and C0002-4-f samples experienced the heating/cooling cycle up to 110°C under the laboratory field conditions, the electron microprobe analysis, and the X-ray tomography with synchrotron radiation. The laboratory heating TRM and/or laboratory IRM components were recognized for these samples in THD and low-field AF steps. Additionally, the origin trending components with different directions from the artificial components were recognized for the Ryugu A0026 and C0002-4-f samples in the AF ranges of 10–32.5 mT and 0–22 mT, respectively (Figures 9a and 9b). The lack of unidirectionality between the 0–10 and 10–32.5 mT AF level components of Ryugu A0026 sample indicates that the latter component is unlikely the IRM overprint and likely the record of ancient field. Moreover, the origin trending components show similar NRM intensities: 0.01 and 0.02 Am²/kg for the A0026 and C0002-4-f samples, respectively, suggesting the similar remanence acquisition mechanism of these components. The VRM acquired at 65°C for 20–200 years is estimated to be demagnetized as the result of laboratory heating at 110°C for 5 min, assuming the magnetocrystalline anisotropy dominating magnetite and using the relaxation equation in Pullaiah et al. (1975). The paleointensity values of the Ryugu A0026 and C0002-4-f samples using the SIRM paleointensity constant of 3,000 μT with adopting the uncertainty from 1,500 to 6,000 μT (Gattacceca & Rochette, 2004) were estimated to be 31–260 μT and 18–704 μT, respectively. The large uncertainty in paleointensity was due to the uncertainty in the paleointensity constant to cover the possibility of various magnetic minerals, such as magnetite, titanomagnetite, pyrrhotite, and FeNi alloys, and the uncertainty in the selection of AFD segments in paleointensity estimations, due to the lack of detailed information on NRM carriers.

The coercivity range of the origin trending NRM components corresponds to the middle-coercivity range and is interpreted as the remanence carried by framboidal magnetite. The paleofield strengths were calculated using the SIRM paleointensity constant value of 3,318 μT and the ratio of NRM to IRM as 3,318 × ΔNRM/ΔIRM, where the ΔNRM and ΔIRM are the NRM and IRM intensities demagnetized in same demagnetization segment, respectively. The paleofield strengths for the origin trending components were estimated to be 69–144 μT and 41–390 μT for the Ryugu A0026 and C0002-4-f samples, respectively (Figures 9c and 9d). The paleointensity values for C0002-4-f sample sharply decreased with increasing AFD step below 10 mT (Figure 9d), resulting in large uncertainty in paleofield estimation. The exceptionally strong paleointensity for C0002-4-f sample in AFD step below 10 mT may arise from the exceptional THD treatment in the SIRM paleointensity method and unlikely arise from artificial IRM, and the effect of exceptional THD should be evaluated to optimize the AFD segments in paleointensity estimation. No significant relaxation of NRM were observed for the A0064-FO018 and C0023-FC009 samples suggest that the effects of VRM acquired during the transportation for ∼2 years and on the curation facility for ∼0.5 years were likely negligible for the SIRM paleointensity estimation of middle-coercivity range. Although the uncertainty in paleointensity values should be reduced in further research, the framboidal magnetites in Ryugu samples have recorded strong magnetic field values.

The framboidal magnetite in Ryugu samples crystallized and grew by aqueous alteration in the parent body of asteroid Ryugu, and the subsequent temperature increase was limited to ∼50°C (Nakamura et al., 2022). Features indicative of strong deformation or shock melting were not observed in the Ryugu samples, and the Ryugu samples did not experience intense shock (Nakamura et al., 2022). Therefore, the stable NRM components in the middle-coercivity ranges were unlikely to be TRM or shock remanent magnetization and were probably CRM acquired during aqueous alteration at 3.1–6.8 Myr after the formation of the first minerals, calcium-aluminum-rich inclusions (Yokoyama et al., 2022). Moreover, the limitation of temperature increase indicates no significant disturbance from pTRM.

Because the paleointensity values are estimated assuming TRM in the SIRM paleointensity method, the remanence intensity ratio of CRM acquired during aqueous alteration to TRM should be evaluated to understand the uncertainty of recovered paleointensity. Sridhar et al. (2021) suggested that magnetite crystals in carbonaceous chondrites likely formed through two different pathways; magnetite grains in framboid and plaquette formed through the dissolution of sulfide and precipitation of magnetite (CR, CI, and ungrouped C2 chondrites), while magnetite grains in other forms formed through the pseudomorphic replacement of metal (CO, CM, and CR chondrites). Borlina et al. (2022) proposed that the magnetite formed through the replacement of Fe-Ni metal likely inherited non-unidirectional pre-accretionary remanences of metal, while meteorite containing magnetite framboids and plaquettes likely recorded CRM as the grains grew through their blocking volumes during precipitation. Because the remanence acquisition efficiency of grain growth CRM is considered to be lower than that of TRM (e.g., McClelland, 1996), the strong magnetic field values estimated assuming TRM are regarded as a lower limit. The NRM of the Ryugu A0026 and C0002-4-f samples did not show the significant intensities above 22–32.5 mT AF steps (Figures 9a and 9b), while the magnetite and pyrrhotite in Ryugu samples have the IRM component above the AF level (Figures 1, 4, and 5). Because the pyrrhotite grains crystallized and grew during aqueous alteration (Nakamura et al., 2022), the deficient NRM components may be due to the relaxation during 4.6 Gyr or the low acquisition efficiency of CRM in pyrrhotite with respect to framboidal magnetite. Since the magnetite in Ryugu samples showed TRM components above 20–30 mT AF range (Figures 4 and 5) and the magnetocrystalline anisotropy energy dominated magnetite likely have microcoercivity up to 37.5 mT (Dunlop & Özdemir, 1997), the magnetite grains may lack the NRM components in the higher coercivity range. The magnetite grain size of higher coercivity component likely smaller than that of lower coercivity component, and the deficiency of NRM component may be the record of weak or null ambient field in the late stage of aqueous alteration or due to the relaxation during 4.6 Gyr.

The similar paleointensity values obtained from two distant landing sites (A0026 in TD1 and C0002-4-f in TD2) may indicate that the magnetic field was homogeneous in Ryugu's parent planetesimal size as the source of the strong field, although the possibility that two particles originated from the neighboring area of Ryugu's parent planetesimal cannot be reduced. Ryugu is probably from either the Polana or Eulalia families in the inner main belt, whose parent bodies are estimated to be ∼100 km in diameter (Sugita et al., 2019). The dynamo field in the parent body of Ryugu is unlikely to be a source of a strong magnetic field, because the thermal modeling of parent body of Ryugu indicated the internal temperature less than ∼100°C (Nakamura et al., 2022) and the elemental abundance of Ryugu material is consistent with CI composition (Yokoyama et al., 2022), which strongly supports that Ryugu materials came from an undifferentiated parent body. The passage of the magnetosphere of other body is also unlikely as the source of the strong field, because the free-fall times were much shorter than the CRM acquisition-time, although the possibility that the parent body of Ryugu was transiently captured by a large body and acquired the strong remanence in its magnetosphere cannot be declined. Thus, the most likely candidate for the long-wavelength and strong field ranging from 41 to 390 μT is the magnetic field of the protoplanetary disk, suggesting that the protoplanetary disk existed at the disk location of Ryugu's parent planetesimal when framboidal magnetite precipitated from the aqueous fluid. Because the lower bound of paleointensity (41 μT) is higher than the paleointensity values of carbonaceous chondrites with framboidal magnetite, including Tagish Lake, and likely originated in distal solar system (Bryson, Weiss, Biersteker, et al., 2020; Bryson, Weiss, Lima, et al., 2020; Sridhar et al., 2021), the orbital evolution of Ryugu's parent body until/during the aqueous alteration and the heterogeneities in the solar nebula magnetic field (Borlina et al., 2021; Fu et al., 2021) should be evaluated on the basis of various constraints in future study. Based on the nature and characteristics of the magnetic record revealed in this study, the uncertainty in the paleointensity estimate should be reduced in further research, which will provide critical information concerning the evolution of the early solar system, such as the disk lifetime and time-spatial change in the accretion rate.

5 Conclusion

This study conducted systematic rock magnetic measurements and SIRM paleointensity calibration experiments on returned samples from asteroid Ryugu and carbonaceous chondrites (Orgueil and Tagish Lake) to evaluate the remanence carriers of the Ryugu sample and its ability to record paleomagnetic information. The signatures of framboidal magnetite, coarse-grained magnetite, and pyrrhotite are recognized in the Ryugu sample, and framboidal magnetite is the dominant remanence carrier in the middle-coercivity range. The median value of the SIRM paleointensity constant obtained from the two Ryugu samples is 3,318 ± 1,038 μT, which is close to the constant value averaged for magnetite, titanomagnetite, pyrrhotite, and FeNi alloys and is widely used in SIRM paleointensity experiments. The paleointensity values estimated using the obtained SIRM paleointensity constant for the Ryugu sample indicate a strong magnetic field with a nebular origin, suggesting that Sun's protoplanetary disk existed at the disk location of Ryugu's parent planetesimal when framboidal magnetite precipitated from the aqueous fluid.

Acknowledgments

M. Sato is supported by JSPS KAKENHI Grant JP21H01140.

Open Research

Data Availability Statement

Data from this paper are archived at the UTokyo Repository (Sato, 2022).

References

Arakawa, M., Saiki, T., Wada, K., Ogawa, K., Kadono, T., Shirai, K., et al. (2020). An artificial impact on the asteroid (162173) Ryugu formed a crater in the gravity-dominated regime. Science, 368(6486), 67–71. https://doi.org/10.1126/science.aaz1701
10.1126/science.aaz1701
CASADSPubMedWeb of Science®Google Scholar
Borlina, C. S., Weiss, B. P., Bryson, J. F., Bai, X. N., Lima, E. A., Chatterjee, N., & Mansbach, E. N. (2021). Paleomagnetic evidence for a disk substructure in the early solar system. Science Advances, 7(42), eabj6928. https://doi.org/10.1126/sciadv.abj6928
10.1126/sciadv.abj6928
CASADSPubMedWeb of Science®Google Scholar
Borlina, C. S., Weiss, B. P., Bryson, J. F. J., & Armitage, P. J. (2022). Lifetime of the outer solar system nebula from carbonaceous chondrites. Journal of Geophysical Research: Planets, 127(7), e2021JE007139. https://doi.org/10.1029/2021JE007139
10.1029/2021JE007139
CASADSWeb of Science®Google Scholar
Bryson, J. F. J., Weiss, B. P., Biersteker, J. B., King, A. J., & Russell, S. S. (2020). Constraints on the distances and timescales of solid migration in the early solar system from meteorite magnetism. The Astrophysical Journal, 896(2), 103. https://doi.org/10.3847/1538-4357/ab91ab
10.3847/1538-4357/ab91ab
CASADSWeb of Science®Google Scholar
Bryson, J. F. J., Weiss, B. P., Lima, E. A., Gattacceca, J., & Cassata, W. S. (2020). Evidence for asteroid scattering and distal solar system solids from meteorite paleomagnetism. The Astrophysical Journal, 892(2), 126. https://doi.org/10.3847/1538-4357/ab7cd4
10.3847/1538-4357/ab7cd4
CASADSWeb of Science®Google Scholar
Cournede, C., Gattacceca, J., Gounelle, M., Rochette, P., Weiss, B., & Zanda, B. (2015). An early solar system magnetic field recorded in CM chondrites. Earth and Planetary Science Letters, 410, 62–74. https://doi.org/10.1016/j.epsl.2014.11.019
10.1016/j.epsl.2014.11.019
CASADSWeb of Science®Google Scholar
Day, R., Fuller, M., & Schmidt, V. A. (1977). Hysteresis properties of titanomagnetites: Grain size and composition dependence. Physics of the Earth and Planetary Interiors, 13(4), 260–267. https://doi.org/10.1016/0031-9201(77)90108-x
10.1016/0031-9201(77)90108-X
ADSWeb of Science®Google Scholar
Dekkers, M. J., Mattéi, J.-L., Fillion, G., & Rochette, P. (1989). Grain-size dependence of the magnetic behavior of pyrrhotite during its low-temperature transition at 34 K. Geophysical Research Letters, 16(8), 855–858. https://doi.org/10.1029/gl016i008p00855
10.1029/GL016i008p00855
CASADSWeb of Science®Google Scholar
Dunlop, D. J., & Özdemir, Ö. (1997). Rock magnetism: Fundamentals and Frontiers (p. 573). Cambridge University Press.
10.1017/CBO9780511612794
Google Scholar
Fu, R., Kehayias, P., Weiss, B. P., Schrader, D. L., Bai, X.-N., & Simon, J. B. (2020). Weak magnetic fields in the outer solar nebula recorded in CR chondrites. Journal of Geophysical Research: Planets, 125(5), e2019JE006260. https://doi.org/10.1029/2019je006260
10.1029/2019JE006260
ADSWeb of Science®Google Scholar
Fu, R., Weiss, B. P., Lima, E. A., Harrison, R. J., Bai, X.-N., Desch, S. J., et al. (2014). Solar nebula magnetic fields recorded in the Semarkona meteorite. Science, 346(6213), 1089–1092. https://doi.org/10.1126/science.1258022
10.1126/science.1258022
CASADSPubMedWeb of Science®Google Scholar
Fu, R. R., Volk, M. W. R., Bilardello, D., Libourel, G., Lesur, G. R. J., & Ben Dor, O. (2021). The fine-scale magnetic history of the Allende meteorite: Implications for the structure of the solar nebula. AGU Advances, 2(3), e2021AV000486. https://doi.org/10.1029/2021av000486
10.1029/2021AV000486
ADSWeb of Science®Google Scholar
Gattacceca, J., & Rochette, P. (2004). Toward a robust normalized magnetic paleointensity method applied to meteorites. Earth and Planetary Science Letters, 227(3–4), 377–393. https://doi.org/10.1016/j.epsl.2004.09.013
10.1016/j.epsl.2004.09.013
CASADSWeb of Science®Google Scholar
Gattacceca, J., Weiss, B. P., & Gounelle, M. (2016). New constraints on the magnetic history of the CV parent body and the solar nebula from the Kaba meteorite. Earth and Planetary Science Letters, 455, 166–175. https://doi.org/10.1016/j.epsl.2016.09.008
10.1016/j.epsl.2016.09.008
CASADSWeb of Science®Google Scholar
Harrison, R. J., & Feinberg, J. M. (2008). FORCinel: An improved algorithm for calculating first-order reversal curve distributions using locally weighted regression smoothing. Geochemistry, Geophysics, Geosystems, 9(5), Q05016. https://doi.org/10.1029/2008gc001987
10.1029/2008GC001987
ADSWeb of Science®Google Scholar
Harrison, R. J., Zhao, X., Hu, P., Sato, T., Heslop, D., Muxworthy, A. R., et al. (2019). Simulation of remanent, transient, and induced FORC diagrams for interacting particles with uniaxial, cubic, and hexagonal anisotropy. Journal of Geophysical Research: Solid Earth, 124(12), 12404–12429. https://doi.org/10.1029/2019jb018050
10.1029/2019JB018050
ADSWeb of Science®Google Scholar
Heider, F., Dunlop, D. J., & Soffel, H. C. (1992). Low-temperature and alternating field demagnetization of saturation remanence and thermoremanence in magnetite grains (0.037 μm to 5 mm). Journal of Geophysical Research, 97(B6), 9371–9381. https://doi.org/10.1029/91jb03097
10.1029/91JB03097
ADSWeb of Science®Google Scholar
Kato, C., Sato, M., Yamamoto, Y., Tsunakawa, H., & Kirschvink, J. L. (2018). Paleomagnetic studies on single crystals separated from the middle Cretaceous Iritono granite. Earth Planets and Space, 70(176), 176. https://doi.org/10.1186/s40623-018-0945-y
10.1186/s40623-018-0945-y
ADSWeb of Science®Google Scholar
McClelland, E. (1996). Theory of CRM acquired by grain growth, and its implications for TRM discrimination and paleointensity determination in igneous rocks. Geophysical Journal International, 126(1), 271–280. https://doi.org/10.1111/j.1365-246x.1996.tb05285.x
10.1111/j.1365-246X.1996.tb05285.x
ADSWeb of Science®Google Scholar
Morota, T., Sugita, S., Cho, Y., Kanamaru, M., Tatsumi, E., Sakatani, N., et al. (2020). Sample collection from asteroid (162173) Ryugu by Hayabusa 2: Implications for surface evolution. Science, 368, 654–659.
10.1126/science.aaz6306
CASADSPubMedWeb of Science®Google Scholar
Moskowitz, B. M., Jackson, M., & Kissel, C. (1998). Low-temperature magnetic behavior of titanomagnetites. Earth and Planetary Science Letters, 157(3–4), 141–149. https://doi.org/10.1016/s0012-821x(98)00033-8
10.1016/S0012-821X(98)00033-8
CASADSWeb of Science®Google Scholar
Nakamura, T., Matsumoto, M., Amano, K., Enokido, Y., Zolensky, M. E., Mikouchi, T., et al. (2022). Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples. Science, eabn8671. https://doi.org/10.1126/science.abn8671
10.1126/science.abn8671
PubMedGoogle Scholar
O'Reilly, W., Hoffman, V., Chouker, A. C., Soffel, H. C., & Menyeh, A. (2000). Magnetic properties of synthetic analogues of pyrrhotite ore in the grain size range 1–24 μm. Geophysical Journal International, 142(3), 669–683. https://doi.org/10.1046/j.1365-246x.2000.00169.x
10.1046/j.1365-246x.2000.00169.x
ADSWeb of Science®Google Scholar
Pullaiah, G., Irving, E., Buchan, K. L., & Dunlop, D. J. (1975). Magnetization changes caused by burial and uplift. Earth and Planetary Science Letters, 28(2), 133–143. https://doi.org/10.1016/0012-821x(75)90221-6
10.1016/0012-821X(75)90221-6
ADSWeb of Science®Google Scholar
Sato, M. (2022). Data in “Rock magnetic characterization of returned samples from asteroid (162173) Ryugu: Implications for paleomagnetic interpretation and paleointensity estimation.”. Retrieved from http://hdl.handle.net/2261/0002005590
Google Scholar
Sato, M., Yamamoto, S., Yamamoto, Y., Okada, Y., Ohno, M., Tsunakawa, H., & Maruyama, S. (2015). Rock-magnetic properties of single zircon crystals sampled from the Tanzawa tonalitic pluton, central Japan. Earth Planets and Space, 67(1), 150. https://doi.org/10.1186/s40623-015-0317-9
10.1186/s40623-015-0317-9
ADSWeb of Science®Google Scholar
Sawada, H., Okazaki, R., Tachibana, S., Sakamoto, K., Takano, Y., Okamoto, C., et al. (2017). Hayabusa2 sampler: Collection of asteroidal surface material. Space Science Reviews, 208(1), 8–106. https://doi.org/10.1007/s11214-017-0338-8
10.1007/s11214-017-0338-8
Web of Science®Google Scholar
Sridhar, S., Bryson, J. F., King, A. J., & Harrison, R. J. (2021). Constraints on the ice composition of carbonaceous chondrites from their magnetic mineralogy. Earth and Planetary Science Letters, 576, 117243. https://doi.org/10.1016/j.epsl.2021.117243
10.1016/j.epsl.2021.117243
CASWeb of Science®Google Scholar
Sugita, S., Honda, R., Morota, T., Kameda, S., Sawada, H., Tatsumi, E., et al. (2019). The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes. Science, 364, eaaw0422.
10.1126/science.aaw0422
CASWeb of Science®Google Scholar
Tachibana, S., Sawada, H., Okazaki, R., Takano, Y., Sakamoto, K., Miura, Y. N., et al. (2022). Pebbles and sand on asteroid (162173) Ryugu: In situ observation and particles returned to Earth. Science, 375, 1011–1016.
10.1126/science.abj8624
CASADSPubMedWeb of Science®Google Scholar
Thorpe, A. N., Senftle, F. E., & Grant, J. R. (2002). Magnetic study of magnetite in the Tagish Lake meteorite. Meteoritics & Planetary Sciences, 37(5), 763–771. https://doi.org/10.1111/j.1945-5100.2002.tb00853.x
10.1111/j.1945-5100.2002.tb00853.x
CASADSWeb of Science®Google Scholar
Wang, H., Weiss, B. P., Bai, X.-N., Downey, B. G., Wang, J., Wang, J., et al. (2017). Lifetime of the solar nebula constrained by meteorite paleomagnetism. Science, 355(6325), 623–627. https://doi.org/10.1126/science.aaf5043
10.1126/science.aaf5043
CASADSPubMedWeb of Science®Google Scholar
Watanabe, S., Hirabayashi, M., Hirata, N., Hirata, N., Noguchi, R., Shimaki, Y., et al. (2019). Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu—A spinning top-shaped rubble pile. Science, 364(6437), eaav8032–eaav8272.
10.1126/science.aav8032
Web of Science®Google Scholar
Weiss, B. P., Bai, X.-N., & Fu, R. R. (2021). History of the solar nebula from meteorite paleomagnetism. Science Advances, 7(1), eaba5967. https://doi.org/10.1126/sciadv.aba5967
10.1126/sciadv.aba5967
ADSPubMedWeb of Science®Google Scholar
Weiss, B. P., & Tikoo, S. M. (2014). The lunar dynamo. Science, 346(6214), 1246753. https://doi.org/10.1126/science.1246753
10.1126/science.1246753
PubMedWeb of Science®Google Scholar
Yada, T., Abe, M., Okada, T., Nakato, A., Yogata, K., Miyazaki, A., et al. (2022). Preliminary analysis of the Hayabusa2 samples returned from C-type asteroid Ryugu. Nature Astronomy, 6, 214–220.
10.1038/s41550-021-01550-6
ADSWeb of Science®Google Scholar
Yokoyama, T., Nagashima, K., Nakai, I., Young, E. D., Abe, Y., Aleon, J., et al. (2022). Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites. Science, abn7850. https://doi.org/10.1126/science.abn7850
10.1126/science.abn7850
Google Scholar
Yoshikawa, K., Terui, F., Mimasu, Y., & Ogawa, N. (2016). Hayabusa2 attitude operation during Earth swing-by and cruising. Proceedings of the Space Sciences and Technology Conference, 60, 6–11.
Google Scholar

Citing Literature

Volume127, Issue11

November 2022

e2022JE007405

Rock Magnetic Characterization of Returned Samples From Asteroid (162173) Ryugu: Implications for Paleomagnetic Interpretation and Paleointensity Estimation

Abstract

Key Points

Plain Language Summary

1 Introduction