Hayabusa‐returned sample curation in the Planetary Material Sample Curation Facility of JAXA

Abstract– The Planetary Material Sample Curation Facility of JAXA (PMSCF/JAXA) was established in Sagamihara, Kanagawa, Japan, to curate planetary material samples returned from space in conditions of minimum terrestrial contaminants. The performances for the curation of Hayabusa‐returned samples had been checked with a series of comprehensive tests and rehearsals. After the Hayabusa spacecraft had accomplished a round‐trip flight to asteroid 25143 Itokawa and returned its reentry capsule to the Earth in June 2010, the reentry capsule was brought back to the PMSCF/JAXA and was put to a series of processes to extract recovered samples from Itokawa. The particles recovered from the sample catcher were analyzed by electron microscope, given their ID, grouped into four categories, and preserved in dimples on quartz slide glasses. Some fraction of them has been distributed for initial analyses at NASA, and will be distributed for international announcement of opportunity (AO), but a certain fraction of them will be preserved in vacuum for future analyses.     

Sylvite and halite on particles recovered from 25143 Itokawa: A preliminary report

We observed cross sectional ultra‐thin sections near the surface of 12 particles recovered from the S‐type asteroid Itokawa by the Hayabusa spacecraft in 2010, using spherical aberration–corrected STEM and conventional TEM. Although their mineralogy is almost identical to the equilibrated LL chondrites and therefore basically anhydrous, micrometer‐to‐submicrometer‐sized sylvite was identified on the surface of Itokawa particle RA‐QD02‐0034. Separately, micrometer‐sized halite was also identified on the surface of Itokawa particle RA‐QD02‐0129. Detailed inspection of the sample processing procedures at the JAXA's Planetary Materials Sample Curation Facility and textural observation of the sylvite and halite indicate that they were clearly present on two Itokawa particles before they were removed from Clean Chamber #2 at JAXA. However, there is no direct evidence for their extraterrestrial origin at present. If the sylvite and halite are extraterrestrial, their presence suggests that they may be more abundant on the surface of S‐type asteroids than previously thought.     

Earth impact probability of the Asteroid (25143) Itokawa to be sampled by the spacecraft Hayabusa

The Japanese spacecraft Hayabusa is planed to reach the Asteroid Itokawa in September 2005, and to bring back some samples of its surface to Earth in 2007. We have studied the future possible evolution of this asteroid by integrating numerically over 100 Myr a set of 39 initially indistinguishable orbits (clones), obtained either by small variations of the nominal initial conditions, or by using different computers (introducing different round-off errors). The results indicate that an Earth impact of this 500-m-size asteroid is likely within a million years, which is only a factor of four larger than the average impact frequency of asteroids of this size. The mission Hayabusa may thus sample a good candidate for being among the next 500-m-size Earth impactors.     

Thermal modeling for a parent body of Itokawa

We modeled the possible parent bodies of Itokawa, which was heated within by the decay energy of ²⁶Al. Based on mineralogic studies of dust particles derived from Itokawa by the Hayabusa spacecraft, it appeared that they were thermally metamorphosed at a peak temperature of 800 °C, and kept at 700 °C or higher at 7.6 Myr after CAI formation. Our numerical results show that the parent bodies of Itokawa would have been larger than 20 km in radius and accreted at a period between 1.9 and 2.2 Myr after CAI formation, to satisfy mineralogic and isotopic evidence from dust particles.     

Terrestrial weathering of ordinary chondrites in nature and continuing during laboratory storage and processing: Review and implications for Hayabusa sample integrity

Abstract– The Hayabusa mission recently returned the first samples from an ordinary chondrite (OC) parent body. Olivine, low‐Ca pyroxene, and kamacite compositions fall within the known ranges of minerals from LL4 to LL6 chondrites. Hayabusa samples are being processed and stored in a pure N₂ atmosphere. However, during recovery, prior to receiving, and during preliminary examination, some Hayabusa samples were briefly exposed to terrestrial atmosphere. Some of the minerals already identified in the Hayabusa samples (olivine, sulfides) are known to be among the most vulnerable to weathering reactions in moist, oxidizing terrestrial environments. Oxidation of Fe in metal, sulfides, and ferrous silicates is ubiquitous in naturally weathered OC finds, in samples of falls subjected to even a few decades of weathering before recovery, and in OC falls recovered and curated promptly after recovery. All prerecovery oxidation, hydrolysis, hydration, and product‐forming phenomena documented to affect OC finds have been documented to continue in OC samples in curatorial and laboratory settings, producing mineralogical and textural effects at scales easily discernable by electron microscopy, on timescales of decades. Hayabusa samples will be exposed to similar terrestrial conditions at times throughout sample processing, allocation, and examination. Maximizing the science yield from these important samples requires thorough understanding of how LL chondrite minerals like those in the Hayabusa samples react with terrestrial moisture and oxidants in support of proper planning for maintaining Hayabusa sample integrity after allocation, and for proper anticipation of the effects of inevitable exposure to Earth’s atmosphere during storage and examination in terrestrial analytical laboratories.     

Comparing analytical and numerical approaches to meteoroid orbit determination using Hayabusa telemetry

Fireball networks establish the trajectories of meteoritic material passing through Earth's atmosphere, from which they can derive pre‐entry orbits. Triangulated atmospheric trajectory data require different orbit determination methods to those applied to observational data beyond the Earth's sphere of influence, such as telescopic observations of asteroids. Currently, the vast majority of fireball networks determine and publish orbital data using an analytical approach, with little flexibility to include orbital perturbations. Here, we present a novel numerical technique for determining meteoroid orbits from fireball network data and compare it to previously established methods. The re‐entry of the Hayabusa spacecraft, with its known pre‐Earth orbit, provides a unique opportunity to perform this comparison as it was observed by fireball network cameras. As initial sightings of the Hayabusa spacecraft and capsule were made at different altitudes, we are able to quantify the atmosphere's influence on the determined pre‐Earth orbit. Considering these trajectories independently, we found the orbits determined by the novel numerical approach to align closer to JAXA's telemetry in both cases. Using simulations, we determine the atmospheric perturbation to become significant at ~90 km—higher than the first observations of typical meteorite dropping events. Using further simulations, we find the most substantial differences between techniques to occur at both low entry velocities and Moon passing trajectories. These regions of comparative divergence demonstrate the need for perturbation inclusion within the chosen orbit determination algorithm.     

Fundamentally distinct outcomes of asteroid collisional evolution and catastrophic disruption

The outcomes of asteroid collisional evolution are presently unclear: are most asteroids larger than 1 km size gravitational aggregates reaccreted from fragments of a parent body that was collisionally disrupted, while much smaller asteroids are collisional shards that were never completely disrupted? The 16 km mean diameter S-type asteroid 433 Eros, visited by the NEAR mission, has surface geology consistent with being a fractured shard. A ubiquitous fabric of linear structural features is found on the surface of Eros and probably indicates a globally consolidated structure beneath its regolith cover. Despite the differences in absolute scale and in lighting conditions for NEAR and Hayabusa, similar features should have been found on 25143 Itokawa if present. This much smaller, 320 m diameter S-asteroid was visited by the Hayabusa spacecraft. Comparative analyses of Itokawa and Eros geology reveal fundamental differences, and interpretation of Eros geology is illuminated by comparison with Itokawa. Itokawa lacks a global lineament fabric, and its blocks, craters, and regolith may be inconsistent with formation and evolution as a fractured shard, unlike Eros. An object as small as Itokawa can form as a rubble pile, while much larger Eros formed as a fractured shard. Itokawa is not a scaled-down Eros, but formed by catastrophic disruption and reaccumulation.     

Three‐dimensional microstructure of samples recovered from asteroid 25143 Itokawa: Comparison with LL5 and LL6 chondrite particles

In this study, the three‐dimensional (3‐D) microstructure of 48 Itokawa regolith particles was examined by synchrotron microtomography at SPring‐8 during the preliminary examination of Hayabusa samples. Moreover, the 3‐D microstructure of particles collected from two LL6 chondrites (Ensisheim and Kilabo meteorites) and an LL5 chondrite (Tuxtuac meteorite) was investigated by the same method for comparison. The modal abundances of minerals, especially olivine, bulk density, porosity, and grain size are similar in all samples, including voids and cracks. These results show that the Itokawa particles, which are surface materials from the S‐type asteroid Itokawa, are consistent with the LL chondrite materials in terms of not only elemental and isotopic composition of the minerals but also 3‐D microstructure. However, we could not determine whether the Itokawa particles are purely LL5, LL6, or a mixture of the two. No difference between the particles collected from Rooms A and B of the sample chamber, corresponding to the sampling sequence of the spacecraft's second and first touchdowns, respectively, was detected because of the statistically small amount of particles from Room B.     

Radar observations of asteroid 25143 Itokawa (1998 SF36)

Abstract— We observed 25143 Itokawa, the target of Japan's Hayabusa (MUSES‐C) sample‐return mission, during its 2001 close approach at Arecibo on twelve dates during March 18‐April 9 and at Goldstone on nine dates during March 20‐April 2. We obtained delay‐Doppler images with range resolutions of 100 ns (15 m) at Arecibo and 125 ns (19 m) at Goldstone. Itokawa's average circular polarization ratio at 13 cm, 0.26 ± 0.04, is comparable to that of Eros, so its cm‐to‐m surface roughness probably is comparable to that on Eros. Itokawa's radar reflectivity and polarization properties indicate a near‐surface bulk density within 20% of 2.5 g cm^?3. We present a preliminary estimate of Itokawa's shape, reconstructed from images with rather limited rotation‐phase coverage, using the method of Hudson (1993) and assuming the lightcurve‐derived spin period (12.132 hr) and pole direction (ecliptic long., lat. = 355°, ?84°) of Kaasalainen et al. (2003). The model can be described as a slightly asymmetrical, slightly flattened ellipsoid with extents along its principal axes of 548 times 312 times 276 m ± 10%. Itokawa's topography is very subdued compared to that of other asteroids for which spacecraft images or radar reconstructions are available. Similarly, gravitational slopes on our Itokawa model average only 9° and everywhere are less than 27°. The radar‐refined orbit allows accurate identification of Itokawa's close planetary approaches through 2170. If radar ranging planned for Itokawa's 2004 apparition succeeds, then tracking of Hayabusa during its 2005 rendezvous should reveal Yarkovsky perturbation of the asteroid's orbit.     

Combining IR and X‐ray microtomography data sets: Application to Itokawa particles and to Paris meteorite

In the near future, a new generation of sample return missions (Hayabusa2, OSIRIS‐REx, MMX, etc.) will collect samples from small solar system bodies. To maximize the scientific outcome of laboratory studies and minimize the loss of precious extraterrestrial samples, an analytical sequence from less destructive to more destructive techniques needs to be established. In this work, we present a combined X‐ray and IR microtomography applied to five Itokawa particles and one fragment of the primitive carbonaceous chondrite Paris. We show that this analytical approach is able to provide a 3‐D physical and chemical characterization of individual extraterrestrial particles, using the measurement of their 3‐D structure and porosity, and the detection of mineral and organic phases, and their spatial co‐localization in 3‐D. We propose these techniques as an efficient first step in a multitechnique analytical sequence on microscopic samples collected by space missions.     

Chemical and mineralogical compositions of two grains recovered from asteroid Itokawa

Two silicate grains (RB‐QD04‐0049 and RA‐QD02‐0064, whose estimated masses are 0.050 μg and 0.048 μg, respectively) recovered from the asteroid Itokawa by the Hayabusa spacecraft were studied for their mineralogical characteristics by synchrotron X‐ray diffraction and synchrotron X‐ray microtomography and further analyzed for their bulk chemical compositions by instrumental neutron activation analysis (INAA). According to X‐ray tomography, RB‐QD004‐0049 is composed of olivine, high‐Ca pyroxene, plagioclase, Ca‐phosphate, and troilite, whereas RA‐QD002‐0064 entirely consists of olivine. INAA data are consistent with these mineral compositions except for rare earth elements (REEs). Although the grain RB‐QD004‐0049 contains measurable REEs, which seems to be consistent with the presence of Ca‐phosphate, their abundances are anomalously high. Very low abundance of Co implies less than 0.1 mass% of metals in these two grains by calculation, which is in contrast to the result for the previously analyzed grain RA‐QD02‐0049 (Ebihara et al., 2011). FeO/Sc ratios of the grains fall within the range of those for ordinary chondrite olivines, implying that these grains are extraterrestrial in origin. FeO/MnO ratios also confirm this conclusion and further suggest that the Hayabusa grains analyzed in this study are similar to material found in LL chondrites rather than CK chondrites although olivines from LL and CK chondrites have similar Fa# (molar% of Fe relative to [Fe+Mg] in olivine) (~30) to those of the Hayabusa grains including the two grains analyzed in this study.     

Investigation of Thermal Inertia and Surface Properties for Near-earth Asteroid (162173) 1999 JU3

In order to obtain the substantial information about the surface physics and thermal property of the target asteroid (162173) 1999 JU3, which will be visited by Hayabusa 2 in a sample return mission, with the Advanced Thermal Physical Model (ATPM) we estimate the possible thermal inertia distribution over its surface, and infer the major material composition of its surface materials. In addition, the effective diameter and geometric albedo are derived to be D_eff = 1.13 ± 0.03 km, pv = 0.042 ± 0.003, respectively, and the average thermal inertia is estimated to be about (300 ± 50) J m^-2 s^-0.5 K^-1 According to the derived thermal inertia distribution, we infer that the major area on the surface of the target asteroid may be covered by loose materials, such as rock debris, sands, and so on, but few bare rocks may exist in a very small region. In this sense, the sample return mission of Hayabusa 2 is feasible, when it is performed successfully, it will certainly bring significant scientific information to the research of asteroids.     

A flux enhancement measured in energetic particles(E ∼ 60–100 keV) by the epona instrument aboard Giotto close to P⧸Grigg-Skjellerup,and its interpretationas the signature of a companion comet

A significant flux enhancement in energetic particles (E ∼ 60–⩾260 keV),showing internal fine structure interpreted to represent signatures produced during the traversalof various cometary boundaries in P⧸Grigg-Skjellerup, was recorded by the EPONA instrumentaboard spacecraft Giotto on 10 July 1992. A further internally structured flux enhancement withabout the same amplitude, recorded by EPONA in the energy range ∼60–100 keV but detected90×10³ km further on along the Giotto trajectory, is herein compared with theP⧸Grigg-Skjellerup record. Possible explanations for the second flux enhancement areindividually considered and it is suggested, on the basis of the available evidence, that itconstituted the signature of another smaller comet, either having a separate genesis from, ororiginating in a splitting of, the P⧸Grigg-Skjellerup nucleus.     

Space missions to small bodies: asteroids and cometary nuclei

The knowledge of the physical and dynamical properties, distribution, formation, and evolution of small bodies is fundamental to understand how planet formation occurred and, even more importantly, if and how these objects have played a role in the apparition of life on Earth. In the last century, asteroids began to no longer appear as starlike points of light in our telescopes, but to be resolved worlds with distinctly measurable sizes, shapes, and surface morphologies. Only in the last 25 years, the exploration of small bodies by spacecraft has begun and revealed objects widely diverse in formation region, evolution and properties (e.g. shape, albedo density, gravity, regolith size distribution, and porosity). In this paper we will provide a chronological analysis of comet nuclei and asteroids as revealed by space missions. The real breakthrough began with the ESA Giotto mission in 1986 to the comet Halley, while the latest JAXA Hayabusa mission was devoted to hover above the small asteroid Itokawa with a touch-and-go for a sample return of asteroidal regolith. Comet and asteroid science stands at the threshold of a new exceptional era, with many new missions to be devoted to these widely diverse and still poorly known small bodies.     

Laboratory measurement on impact ionization by neutrals and floating potential of a spacecraft during encounter with Halley's Comet

A spacecraft penetrating into the dense cloud of ambient gas and dust particles in the coma of Halley's Comet, is exposed to a bombardment by these particles having a high kinetic energy due to the large velocity of the spacecraft relative to the cometary coma. The interaction of the spacecraft and cometary neutral particles was simulated by using neutral beams of different species directed towards various target materials such as aluminium, gold and the white conductive paint PCB-Z. The kinetic energy of the primary beam covered, depending on the species, the range from about 700 eV up to more than 3 keV and contained, except for H₂O, the expected specific ram energy of $\text{24}\text{eV}\text{amu}$. The highest achievable density corresponded to a distance of slightly less than 10⁴ km off the nucleus. Upon impact on the surface of the target, emission of charged as well as neutral secondary particles was initiated. The yields of the charged particles were derived from measurements of the electrical current produced by secondary ions or electrons. The obtained results for the yields complement other measurements performed in parallel to this work. The derived floating potentials show somewhat lower voltages than obtained by model calculations. It was found that for the metallic targets, the acquired charging potential due to neutral gas impact lies between 4 and 6 V. In the case of PCB-Z, the averaged floating potential amounts to about 14 V.     

The effects of possible contamination by sample holders on samples to be returned by Hayabusa2

Chemical compositions of materials used for new sample holders (vertically aligned carbon nanotubes [VACNTs] and polyimide film), which were developed for the analysis of Hayabusa2‐return samples, were determined by instrumental neutron activation analysis and/or instrumental photon activation analysis, to estimate contamination effects from the sample holders. The synthetic quartz plate used for the sample holders was also analyzed. Ten elements (Na, Al, Cr, Mn, Fe, Ni, Eu, W, Au, and Th) and 14 elements (Na, Al, K, Sc, Ti, Cr, Zn, Ga, Br, Sb, La, Eu, Ir, and Au) could be detected in the VACNTs and polyimide film, respectively. The VACNT data show that contamination by this material with respect to the Murchison meteorite is negligible in terms of the elemental ratios (e.g., Fe/Mn, Na/Al, and Mn/Cr) used for the classification of meteorites due to the extremely low density of VACNTs. However, for the Au/Cr ratio, even small degrees (1.7 wt%) of contamination by VACNTs will change the Au/Cr ratio. Elemental ratios used for the classification of meteorites are only influenced by large amounts of contamination (>60 wt%) of polyimide film, which is unlikely to occur. In contrast, detectable effects on Ti isotopic compositions are caused by >0.1 and >0.3 wt% contamination by VACNTs and polyimide film, respectively, and Hf isotopic changes are caused by >0.1 wt% contamination by VACNTs. The new sample holders (VACNTs and polyimide film) are suitable for chemical classification of Hayabusa2‐return samples, because of their ease of use, applicability to multiple analytical instruments, and low contamination levels for most elements.     

Visible‐IR and Raman microspectroscopic investigation of three Itokawa particles collected by Hayabusa: Mineralogy and degree of space weathering based on nondestructive analyses

Hayabusa‐returned samples offer a unique perspective for understanding the link between asteroids and cosmomaterials available in the laboratory, and provide insights on the early stages of surface space weathering. This study characterizes the mineralogy and the extent of space weathering of the three Itokawa particles RA‐QD02‐0163, RA‐QD02‐0174, and RA‐QD02‐0213 provided by JAXA to our consortium. We report here a series of results based on nondestructive analyses through visible‐near‐infrared reflectance and Raman spectroscopy. Results were obtained on the raw particles, both in their original containers and deposited on diamond windows. Identification of the minerals, characterization of their elemental compositions, and measurements of their relative abundances were led through Raman spectroscopy in punctual and automatic mode. Reflectance spectra in the visible and near‐IR wavelengths constrain the mineralogy of the grains and allow direct comparison with the surface of Itokawa. The spectra reflect the extent of space weathering experienced by the three particles. Particle RA‐QD02‐0163 consists of a heterogeneous mixture of minerals: olivine (Fo₇₆) dominates an assemblage with both Ca‐rich (En₅₀, Wo₅₀) and Ca‐poor (En₈₅) pyroxenes. The elemental compositions of the silicates are consistent with those previously reported for distinct Hayabusa particles. Particles RA‐QD‐0174 and RA‐QD02‐0213 are solely composed of olivine, whose chemical composition is similar to that observed in RA‐QD02‐0163. It has been previously shown that the S‐type asteroid 25143 Itokawa is a breccia of poorly equilibrated LL4 and highly equilibrated LL5 and LL6 materials. The three particles studied here can be related to the least metamorphosed lithology (LL4) based on the high forsterite content of the olivine. Neither carbonaceous matter nor hydrated minerals were detected through Raman on the three allocated particles. The NIR‐VIS reflectance (incidence = 45°, light collection at e = 0°) spectra of the three particles, in particular the 1 μm band, are consistent with the presence of both olivine and pyroxene detected via Raman. The spectra of particles RA‐QD02‐0163 and RA‐QD02‐0213 are also fully compatible with the ground‐based observations of asteroid (25143) Itokawa in terms of both spectral features and slope. By contrast, particle RA‐QD02‐0174 has a similar 1 μm band depth but higher (redder) spectral slope than the surface of Itokawa. This probably reveals a variable extent of space weathering among the regolith particles. RA‐QD02‐0174 may contain a higher amount of nanophase metallic iron and nanophase FeS. Such phases are products by space weathering induced by solar wind, previously detected on other Itokawa particles.     

40Ar/39Ar age of material returned from asteroid 25143 Itokawa

The Hayabusa mission to asteroid 25143, Itokawa, brought back 2000 small particles, which most closely resemble material found in LL4‐6 chondrites. We report an ⁴⁰Ar/³⁹Ar age of 1.3 ± 0.3 Ga for a sample of Itokawa consisting of three grains with a total mass of ~2 μg. This age is lower than the >4.0 Ga ages measured for 75% of LL chondrites but close to one for Y‐790964 and its pairs. The flat ⁴⁰Ar/³⁹Ar release spectrum of the sample suggests complete degassing 1.3 Ga ago. Recent solar heating in Itokawa's current orbit does not appear likely to have reset that age. Solar or impact heating 1.3 Ga ago could have done so. If impact heating was responsible, then the 1.3 Ga age sets an upper bound on the time at which the Itokawa rubble pile was assembled and suggests that rubble pile creation was an ongoing process in the inner solar system for at least the first 3 billion years of solar system history.     

The shape distribution of boulders on Asteroid 25143 Itokawa: Comparison with fragments from impact experiments

Laboratory impact experiments have found that the shape of fragments over a broad size range is distributed around the mean value of the axial ratio 2:√2:1, which is independent of a wide range of experimental conditions. We report the shape statistics of boulders with size of 0.1-30 m on the surface of Asteroid 25143 Itokawa based on high-resolution images obtained by the Hayabusa spacecraft in order to investigate whether their shape distribution is similar to the distribution obtained for fragments (smaller than 0.1 m) in laboratory impact experiments. We also investigated the shapes of boulders with size of 0.1-150 m on Asteroid 433 Eros using a few arbitrary selected images by the NEAR spacecraft, in order to compare those with the shapes on Asteroid Itokawa. In addition, the shapes of small- and fast-rotating asteroids (diameter <200 m and rotation period <1 h), which are natural fragments from past impact events among asteroids, were inferred from archived light curve data taken by ground-based telescopes. The results show that the shape distributions of laboratory fragments are similar to those of the boulders on Eros and of the small- and fast-rotating asteroids, but are different from those on Itokawa. However, we propose that the apparent difference between the boulders of Itokawa and the laboratory fragments is due to the migration of boulders. Therefore, we suggest that the shape distributions of the boulders ranging from 0.1 to 150 m in size and the small- and fast-rotating asteroids are similar to those obtained for the fragments generated in laboratory impact experiments.     

Invariant shape solutions of the spinning three craft Coulomb tether problem

In this paper we study shape-preserving formations of three spacecraft, where the formation keeping forces arise from the electric charges deposed on each craft. Inspired by Lagrange’s 3-body problem, the general conditions that guarantee preservation of the geometric shape of the electrically charged formation are derived. While the classical collinear configuration is a solution to the problem, the equilateral triangle configuration is found to only occur with unbounded relative motion. The three collinear spacecraft problem is analyzed and the possible solutions are categorized based on the spacecraft mass–charge ratio. Precise statements on the number of solutions associated with each category are provided. Finally, a methodology is proposed to study boundedness of the collinear solution that is inspired by past understanding and results for the 3-body problem. Given the initial position and the velocity vectors of each craft along with the charges, analytical solutions are provided describing the resulting relative motion.